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Performance
Analysis of DGPS Positioning Using
Satellite-Based
Augmentation Signals
Authors:
Dr. Mohamed
Abousalem and Mr. Oleg Tubalin, Ashtech Precision Products,
Magellan Corporation, USA
With the growing demand for accurate and reliable
worldwide differential GPS positioning, there has been a
significant move towards the use of real-time GPS augmentation
systems with wide area differential positioning capabilities.
The US Wide Area Augmentation System (WAAS) and the
European Geostationary Navigation Overlay System (EGNOS) are
good examples of such a move.
While these augmentation systems are developed to provide
differential corrections and integrity data for satellite-based
aviation, their signal will be available free of charge to all
other non-aviation satellite positioning users in the respective
coverage areas. Accordingly,
non-aviation GPS users with WAAS/EGNOS-capable receivers will be
able to do differential positioning across the United States and
Europe with a free differential signal and achieve real-time
2-to-3 meter positioning.
The paper will include positioning results using the
new-generation Ashtech G12 GPS receiver utilizing the WAAS and
EGNOS ranging signal and differential corrections.
Positioning results demonstrating 2-3 m positioning
accuracy will be shown under different operating conditions.
GPS Vulnerability to Interference
Author:
Dr Chris Baker, Surveillance Systems Division, Defence Science and
Technology Organisation (DSTO), Australia
Despite the Global
Positioning System (GPS) being a relatively mature technology,
GPS receivers remain highly susceptible to radio frequency (RF)
interference. The GPS modernisation program attempts to address
this susceptibility by implementing additional civilian signals
and higher signal power. An overview of the vulnerability of GPS
receivers in light of this modernisation program is presented,
along with a summary of modern techniques to mitigate the effect
of intentional and unintentional RF interference.
Detection and Implications of Antenna Movements in
Permanent GPS Reference Station Networks
Authors:
Neil Brown and Allison Kealy, Department of Geomatics,
University of Melbourne
James Millner, GPSnet Development Manager, Geodetic
Infrastructure Land Victoria
Permanent GPS reference station networks are
being implemented throughout the world following the
establishment of the Global Positioning System as the primary
means for spatial data acquisition. Often these networks are
used to augment the regional geodetic framework, such as Land
Victoria’s GPSnet in Australia. In Victoria earthquakes and
mass soil movements have been seen to cause variations in the
positions of reference stations over a period of several minutes
to a number of months. In order to ensure a homogenous, reliable
coordinate system that is consistent with the national geodetic
framework (the Australia Fiducial Network) it is therefore
necessary to detect any such changes in reference station
position. This paper examines techniques that can be used to
detect rapid and gradual movements of individual reference
stations within a permanent GPS reference station network. The
techniques are tested using data collected from a receiver
mounted on a precision-engineered device allowing precise
changes in antenna position and processed against GPSnet data
with various configurations of reference stations. From analysis
of these results the effectiveness of the techniques is assessed
in the context of spatial and temporal resolution and reference
station density. The role of movement detection and its
implication in the management of a reference station network
will also be addressed, using GPSnet as a case study.
The Evolution
of GPS-INS Integration from MAGR/SNU to GGP and the Future
Author:
Phil Bruner -
Litton Guidance & Control
Woodland Hills,
California USA
Abstract
to Follow:
GPS: Getting
smaller every year
Author:
Dr Rod Bryant,
Sigtec Navigation Pty Ltd
Over
the last few years, there has been an increasing trend for GPS
modules to become smaller and smaller.
This paper explores the future trends.
Present
C/A code GPS modules have 12 channels and are about the size of
a credit card. Already
there are some modules which are about an inch square.
The next step can be achieved by a combination of further
integration, more compact packaging and different assembly
techniques. We
foresee a module size of about 10 mm x 10 mm by the end of 2001.
Beyond
that, GPS functions will be integrated as macros into larger
chips. The
cellphone is a good example. One
can imagine a cellphone comprised of two blocks – a combined
GPS and Bluetooth block, and a communications block.
This will bring l-commerce (location-based commerce) to
the mass market. Note:
the worldwide forecast for 2003 is 852 Million cellphones
(Dataquest).
The
cellphone will become a universal tool.
It will be your communication device, PDA, Internet
access, personal navigator, and more.
Looking
further ahead, as semiconductor geometries decrease, and
assembly techniques enable smaller and cheaper modules to be
made, so one can envisage disposable GPS.
Imagine a roll of tape.
A fixed length is torn off and affixed to an object.
Parcels and assets could then be tracked round the world.
How long will this take to become a reality?
Five years? Ten
years?
GPS Receiver
Algorithms and System for Operation with Weak Signals
Authors:
Rod
Bryant, Stan Dougan & Eamonn Glennon, Sigtec Navigation Pty
Ltd
A key
requirement for emergency call location (eg E911) and for robust
operation of location-based m-commerce systems is that the
location technology be able to operate in urban canyons and
inside multi-storey carparks, shopping malls and high rise
buildings. Furthermore,
a GPS system able to operate with very weak signals would
provide enormous benefits in urban AVL systems.
The primary problems associated with weak signal
operation are as follows:
1)
In conventional GPS receivers sampling at the correlator
output typically occurs at a sampling interval of the order of
1ms. With weak
signals, however, the signal to noise ratio of these samples is
too low to support lock-in of a phase-locked or frequency-locked
loop. Longer
sampling intervals require that the phase change over the
sampling interval be constrained.
This, in turn, requires impractically high receiver clock
frequency stability and relatively precise knowledge of the time
and receiver location.
2)
With weak signals the signal to noise ratio is too low to
support the extraction of the 50BPS navigation message from the
signal. Aiding data
is therefore required from an external source.
3)
Because the data cannot be extracted, it is not possible
for the receiver to synchronize to the incoming bits, words or
subframes. It is therefore not possible to construct pseudoranges
without prior information.
The paper describes Sigtec Navigation’s
weak signal solution. This
scheme is demonstrably practical with today’s technology and
available communications bandwidths.
It provides sensitivity down to –185dBW and has been
shown to provide reliable positioning inside buildings,
multi-storey car parks and in urban canyons.
Furthermore, in many cases of practical interest, no
aiding at all is required to obtain the full benefit of the
system. Results are
presented from trials of this system mounted around the world.
GPS Management and Support
Authors:
Rebecca Casswell, US Coast Guard Navigation Center
Julie Karner, US Department of State
The
Global Positioning System (GPS) is now an integral part of
information technologies that are fundamental to modern life.
This presentation will briefly describe GPS management,
the plans for GPS modernization, the activities to protect the
user’s access to GPS, and the methods used to encourage the
user involvement in the process.
GPS
is a US sponsored global utility that is important to timing,
communications, transportation, and an unlimited number of other
applications. Technology
has advanced so that it is now reasonable to update the system
to reflect the advances. Modernization
will utilize developments to improve the space and ground
segments.
The
U.S. encourages international use of GPS for increased safety,
efficiency, and scientific research.
This presentation will discuss the U.S.’s international
consultations for global satellite based navigation.
Any
radio signal is useless if it encounters interference.
There are U.S. efforts to mitigate disturbance of the
signal to protect the user and their
The
presentation will also examine some of the current issues and
problems faced by the civil community, identify the near-term
methods of addressing those issues, and describe the plans to
meet future user requirements.
Those issues include user input for continued system
operation and modernization, the reporting and resolution of
intentional and unintentional interference, and the
dissemination of GPS operational information.
U.S. Nationwide Differential GPS System
Author:
Rebecca Casswell, US Coast Guard Navigation Center
The
U.S. Coast Guard maritime Differential GPS (DGPS) system reached
full operating capability (FOC) in March 1999.
Before the FOC declarations, the benefits of the system
were recognized by non-traditional users of navigation signals
in areas near the coastlines and waterways. Demands from the communities not covered from DGPS and a
strong railroad requirement led to studies and a cost-benefit
analysis. This
resulted in the decision to expand the system to cover the
United States.
Once
the maritime system was complete, efforts focused on meeting the
nationwide need. This presentation will describe the status of the program and
some of the problems faced.
It will also present the expected benefits from the
expansion.
First Aircraft
Carrier Autolandings Using Shipboard Relative GPS
Authors:
Glenn Colby,
LCDR Jack Waters, Paul Sousa and Lee Wellons, Naval Air
Systems Command, USA
Marie Lage and
Fred Ventrone, ARINC, Inc
Under
the U.S. Department of Defense’s Joint Precision Approach and
Landing System (JPALS) program, the Navy is responsible for
developing the shipboard component, termed Shipboard Relative
GPS (SRGPS). As a part of the SRGPS effort, a test bed was developed to
demonstrate air traffic control, navigation, and landing
capabilities in the carrier environment.
During testing in January and April, 2001, the Navy
conducted automatic landings to the USS Theodore Roosevelt
(CVN-71) utilizing an F/A-18A Hornet test aircraft.
These tests represented several firsts in the history of
GPS, including:
First ever GPS-based precision approaches to a US Navy
ship (first to any ship by a tactical aircraft)
First ever GPS-based automatic approaches to any ship
First ever 3-dimensional GPS guided approaches to any
ship, and
First real-time demonstration of GPS centimeter level
relative accuracy during shipboard approaches.
The
SRGPS concept is similar to the local differential GPS used
ashore (such as the FAA’s Local Area Augmentation System –
LAAS), but with a few important differences.
Instead of a precise surveyed point, the “reference
station” is installed on a ship.
The ship translates through the water as well as pitch,
rolls and yaws around its center of motion.
In addition the center of motion itself may translate
up/down (heave); side to side (sway), and fore and aft (surge).
Any location away from the center of motion (such as the
GPS antenna location, or aircraft touchdown point) will
experience additional heave, sway, and surge due to the lever
arm effect. Despite
this motion, a single difference calculation between a ship
antenna and aircraft antenna can be made just as accurately as
its shore based counterpart.
The basic difference is simply that the differential correction technique is not used, since absolute
positioning accuracy is not required.
Instead of a correction, the shipboard GPS system
transmits whole satellite measurements to the aircraft, and the
aircraft directly compares aircraft and ship solutions bsed on a
common set of satellites. This
method produces an accurate relative vector between the two
antenna locations which are further translated to (a) the ship
and aircraft centers of motion and (b) the reference flight path
points. For
tailhook equipped aircraft, the reference flight path is defined
as halfway between the 2 and 3 wires on the ship, and the hook
point of the aircraft. These
translations are made through the use of precision Inertial
Navigation System (INS) measurements at each respective
location.
In
addition, unlike the shore approach, the ship flight path is
calculated in a dynamic fashion. The
approach path is stabilized for ship motion until approximately
10 seconds from touchdown. At this point, the aircraft is
commanded to follow the touchdown point sway and heave motions
during the final portion of the approach.
This portion of the approach is termed the deck motion
compensation, or DMC phase.
In the ship yaw axis, the data is stabilized to a
filtered ship heading to allow approaches during ship turns and
low frequency yaw motions.
The
safe landing area aboard ship is much smaller than a standard
runway. Lateral
offsets of more than 3m can result in an aircraft’s wingtip
striking other aircraft parked beside the landing area.
The aircraft’s hook path over the end of the landing
area, termed the hook to ramp clearance, is only 4.3m.
The most demanding requirement for a shore based LAAS
system is 2.0 meters (95%) of navigation system error to
accomplish an autolanding.
Aboard ship, 2m would result in an unacceptable landing
condition. The
SRGPS requires 0.4m (95%) vertical error to accomplish a safe
autolanding. To
meet this requirement, further refinements to the standard
single difference technique were made.
A double difference
calculation is made where all satellite measurements at both
receivers are also compared against a key satellite. The double difference solution is smoothed in a Kalman filter
and the resulting solution is termed the float
solution. From this
float solution a carrier phase integer ambiguity determination
is made using the Lambda method developed by Teunissen.
PSEUDOLITE-BASED
INVERTED POSITIONING AND ITS APPLICATIONS
Authors:
Liwen Dai, Jinling
Wang, Toshiaki Tsujii, Chris Rizos
School of Geomatic
Engineering, University of New South Wales,
Australia
Over the last decade
or so GPS positioning has been playing an increasing role in
both surveying and navigation, andhas become an indispensible
tool for precise relative positioning. However, in some
situations, such as in urban canyons, dam monitoring in valleys
and in deep open-cut mines, the number of visible satellites may
not be sufficient to reliably determine precise coordinates.
Furthermore, it is impossible to use GPS for precise indoor
positioning. Pseudolites, which are ground-based transmitters of GPS-like signals
(i.e. "pseudo-satellites"), can significantly enhance
the satellite geometry, and in principle can even replace the
GPS satellite constellation in some situations, such as for
indoor positioning.
In this paper, the pseudolite-based inverted positioning system, where a
‘constellation’ of GPS receivers with precisely known
'orbit' tracks a mobile pseudolite, is discussed. The system
consists of an array of GPS receivers, the base reference
pseudolite and the mobile pseudolite. The configuration of the
GPS receiver array and the location of both pseudolites have
been studied in terms of the geometry and tracking ability. The
challenges for a pseudolite-based inverted positioning system,
including the near-far problem, signal
interference, time synchronization, multipath,
atmospheric delay effects,
ambiguity resolution, have been investigated. Several
applications based on the pseudolite-based inverted positioning
concept, including indoor navigation, deformation monitoring,
and machine control, are discussed.
Static and kinematic experiments
were carried out using six NovAtel GPS receivers and two
IntegriNautics IN200CXL pseudolite instruments, on the UNSW
campus, during December 2000. The experimental setup and
operating procedures are described in detail. The C/A code and carrier phase measurements have
been processed in an 'inverted' mode. The results indicate that
the accuracy of the inverted code and phase positioning are 1
metre and 2-5 centimetres respectively. The experiments have
indicated that the scenario for pseudolite-based inverted
positioning is feasible.
An Autonomous Navigation System for Satellites Using
GPS Empowered by the High Performance Computing
Authors:
Dr. Anwar Dawood & Dr. Yamming Feng, School of Electrical and
Electronic Systems Engineering, Queensland University of
Technology, Australia
This
paper elaborates on the development of a space born
autonomous navigation system utilising advanced Global
Positioning System (GPS) and high performance computing
technology for future generation of satellite systems.
GPS is a device integrated into the satellite
system to sense spacecraft trajectory and attitude, measure the
relative distance between space vehicles, deliver precise time
synchronisation to spacecraft electronics, and sound the
atmosphere. However, the advances in GPS technology is not
synchronised with the current capability of a standard
spacecraft system to handle all the measurements and provide
on-board processing capacity to use these measurements for
autonomous navigation. Current
spacecraft systems provide very limited on-board computing
capability, and therefore these satellites rely on other devices
to provide information about the spacecraft position such as
star cameras and some times require ground processing of data to
give instructions on appropriate positions of the satellite.
High
Performance Computing (HPC) systems consist of reconfigurable
logic circuits added to a conventional processor to generate a
powerful system for handling intensive computing tasks.
Reconfigurable Computing Technology (RCT) using Field
Programmable Gate Arrays (FPGAs) represents a flexible computing
platform where both the hardware and the software can be
programmed on an application by application basis. This emerging
technology is very promising for a lot of applications
especially satellite systems.
This
paper investigates the deployment of HPC in the context of
real-time reactive computer system on-board the spacecraft in
conjunction with the GPS to implement the autonomous navigation
system. In
particular, the paper introduces the use of a reconfigurable
computer for efficient position and velocity computations of the
spacecraft, with a focus on cost-effective implementation of
precise orbit determination and control algorithms on FPGAs.
The
AUSLIG Online GPS Processing System
Authors:
John Dawson,
Ramesh Govind and John Manning
The Australian
Surveying and Land Information Group (AUSLIG)
The
AUSLIG Online GPS Processing Service provides users with the
facility to submit, via the World Wide Web (WWW), dual
frequency, geodetic quality, GPS RINEX data observed in a
'static' mode, to the AUSLIG GPS processing system and receive
rapid turn-around precise coordinates.
The service is free and provides both ITRF and GDA
coordinates. This
WWW service takes advantage of both the IGS product range and
the IGS GPS network and works with data collected anywhere on
Earth. Aspects of
the design, implementation, usage and future plans of this
system are reviewed.
See
http://www.auslig.gov.au/geodesy/sgc/wwgps.htm
GPS
Synchronised Frequency Hopping Networks
Author:
S. P.
Drake, Surveillance Systems Division, Defence Science and
Technology Organisation, Australia
A
frequency-hopping network is a network whose transmissions hop
from one frequency to another in a pseudo-random manner. They
have become commonplace since the Federal Communications
Commission in the United States stated that transmissions must
be spread-spectrum. Frequency hopping provides security along
with low visibility. For the network to remain connected
synchronisation must be maintained. The Global Positioning
System (GPS) provides a means of doing this cheaply, effectively
and globally. In
this paper we examine the operational limits on a
frequency-hopping network that is synchronised using GPS time.
In particular we derive a relation for the probability that the
network is synchronised, given a hop rate. Predicting the degree
of synchronisation that a GPS synchronised network can maintain
requires a reliable estimate of the errors. For networks whose
users are within line of sight, or confined to a relatively
small area, a number of error sources, such as ionospheric and
tropospheric delay, are likely to be the same, and hence can be
removed from the error budget. With this in mind we measure the
synchronisation of two receivers in a common field of view, and
compare the results with the theoretical prediction.
A Portable GNSS
VHF Data Transmitter (Development and Trials)
Author:
William (Bill)
S. Ely, GNSS Program Officer, Airservices Australia
The
International Civil Aviation Organisation (ICAO) has proposed a
migration from the present ground based aeronautical navigation
aids to a system based on satellite technology.
This migration is likely to occur over an extended
timeframe between the present and approximately 2015.
In order to provide the high levels of accuracy,
integrity, availability and continuity of service required for
sole means aeronautical satellite navigation, a number of
augmentation systems are in the process of development which
will supplement the underlying GPS, and potentially GLONASS and
GALILEO constellations. These
augmentation systems have been largely developed to meet North
American and European requirements, and fail to meet a number
technical, operational, financial and legal requirements in
other areas of the World. To
meet these additional requirements, Australia has proposed a
GRAS. In order to
develop and test the GRAS concept, the GNSSPO has developed a
portable GNSS transmitter which has been deployed extensively on
the eastern coast of Australia from Tasmania to north
Queensland, as well as Norfolk Island.
This paper describes the development of the portable GNSS
transmitter, and the flight test results achieved to date.
GPS
for Aviation: Present and Future
Author:
Professor Per
Enge
Department of
Aeronautics and Astronautics, Stanford University, USA
These
days, the aviation community is steadily increasing its reliance
on the Global Navigation Satellite Systems (GNSS) as the primary
means of navigation for all phases of flight. The most advanced
of the GNSS is the Global Positioning System (GPS). GPS is
already used as a supplemental aid for flight over oceanic
routes, enroute through our domestic airspace, and in crowded
metropolitan airspaces. GPS is also used for a growing number of
airport approach operations. During non-precision approach, it
is used solely for horizontal positioning. Together with
inertial and air data measurements, GPS supports precision
approach at Juneau as well as several other Alaskan cities. In
differential mode, it has been installed to provide vertical
guidance at Newark, Minneapolis, and Chicago O’Hare airports.
To
facilitate this important trend, the international aviation
community is deploying Space-Based Augmentation Systems (SBAS),
Ground-Based Augmentation Systems and Regional Augmentation
Systems. These are all differential GNSS systems. They use
high-quality receivers at known locations to develop corrections
to the signals from the satellites and to bound the error of the
corrected signal. The corrections improve the nominal accuracy
(95%) of stand-alone service, and the error bounds guarantee the
integrity (10-7) of the approach.
GBAS
provides the very high accuracy and integrity required to
support precision approach operations at our busiest airports.
SBAS supports operations over continental areas including
approach operations at small and medium airports. Regional
augmentation systems are similar to SBAS in capability, but they
use terrestrial radios to communicate with the user rather than
satellite links.
At
Stanford, we have supported the development of both SBAS and
GBAS with research and tests directed at the fundamental error
sources, algorithms, safety and operational benefits. In
collaboration with the FAA Technical Center (FAATC), we have
developed complete prototypes of these two systems.
This
talk will describe some exciting current applications of GPS to
aviation. It will also provide a brief report on the development
of SBAS and GBAS in the United States. Next, it will discuss the
current challenges that face GPS use for aviation. These include
safety analyses and radio frequency interference. Finally, it
will describe the long and short term strategies to overcome
these challenges.
Global Positioning System
Signals Under Solar Maximum Conditions
Author:
E. A. Essex
Cooperative Research Centre for Satellite Systems, La Trobe University,
Australia
Solar
activity tends to vary in cycles of around eleven years, with
the current cycle at its maximum intensity at present. This
means that there is more chance of a disruption to GSP signals.
These disruptions may be caused by variations in the
electron density of the ionosphere through which the signal
propagates to a receiver on the ground or in a spacecraft. The
maximum magnitudes of these variations, known as irregularities,
occur at two regions at low latitudes either side of the
magnetic equator and also at high latitudes in the auroral
regions and the polar cap. By monitoring the rapid changes in
the level of the amplitude and phase of the received GPS
signals, known as scintillations, as well as recording the lock
condition of the receiver, it is possible to predict the level
of scintillations which will make the GPS information
unreliable. Currently specially designed GPS receiving systems
are deployed at both high and low latitudes to monitor the level
of scintillations and their effects on the GPS receivers.
Examples will be presented to show the effects of irregularities
on GPS signals. Magnetic storm effects will also be discussed.
Establishment
of GNSS Testing and Validation Facilities in Perth, Western
Australia
Authors:
W.E.
Featherstone, M.P. Stewart, M. Tsakiri, T.A. Forward, N. Penna
Department
of Spatial Sciences, Curtin University of Technology, Australia
R.
McCarthy, Department of Land Administration, Australia
G.
Xanthis, Main Roads Western Australia, Australia
Facilities
for testing and validating GNSS (Global Navigation Satellite
Systems) hardware, firmware, software and users have been
established on and around the Bentley Campus of Curtin
University of Technology. This
comprises a network of fixed pillars that can be used for
testing static-based GNSS positioning (e.g. Stewart et
al., 1998 Survey
Review) and a network of ground monuments that can be used
for testing real-time kinematic (RTK) GNSS positioning (e.g.
Featherstone and Stewart, 2001 Journal of Surveying Engineering).
This paper summarises the establishment and coordination
of these networks and presents a case study of the combined
validation of some RTK GPS systems and their operators for
height determination, which was undertaken in order to set
highway-surveying standards in Western Australia.
It is demonstrated that RTK GPS systems remain subject to
errors that are not reported to the operator, such as incorrect
integer ambiguity resolution and multipath. Further work, in areas such as algorithm development and/or
improved procedures, is thus required to make this a more robust
and reliable positioning tool.
Until this is achieved, users must remain sceptical about
the positional accuracy reported by such systems and apply
additional, independent quality control and quality assurance
procedures.
FedSat Orbit
Determination: Data Processing Strategies and Testing Results
Using Flight Data of BlackJack GPS Space Receiver
Authors:
Yanming Feng,
Miles Moody and Rodney Walker
CRC for
Satellite Systems, Queensland University of Technology,
Australia
The first Australian scientific satellite –FedSat-
is scheduled to be launched in November 2001. FedSat is a low
earth orbiting (LEO) microsatellite conducting space science,
communications, earth remote sensing and engineering
experiments. FedSat will fly NASA’s BlackJack GPS space
receiver to support both its on-board engineering needs,
including real time orbital tracking and timing, and scientific
objectives, such as GPS atmospheric occultation experiment.
The paper will describe a
number of data processing strategies for precise determination
of FedSat orbit in real time and after-the-fact and present the
experimental results from the CHAMP flight mission, which is a
recent German satellite mission, flying the same space receiver.
The data processing is based on JPL’s GISPY-OASIS II software
and additional research and development efforts towards
different processing strategies. As such, different types of
orbit solutions can be produced in real time and a delay from
hours to days after the fact to meet the needs of FedSat
operation and scientific experiments. The experimental results
have shown that the orbit solutions deliverable in real time are
in the level of a few to 20 meters. With time latency of 24
hours to 48 hours, a 3d RMS orbit accuracy of 10 centimetres or
better is achieved, comparing against the official precise orbit
solutions offered by CHAMP mission using final GPS orbit
solutions which are available daily, with delay of 2-4 weeks.
Further work will focus on development of automatic processing
procedures towards FedSat mission.
The Impact of
GNSS on Time and Frequency Measurement
Author:
Dr Peter Fisk,
National Measurement Laboratory, CSIRO, Australia
It
is generally understood that highly accurate time is central to
the operation of the GPS and GLONASS systems, and this is likely
to be true for future GNSS systems. It is less well known that
the GPS system is central to the formation and dissemination of
the international Co-ordinated Universal Time (UTC). This is the
time scale we all use - with various time zone offsets - every
day of our lives.
GPS
has revolutionised the field of time and frequency metrology,
and has facilitated the development and dissemination of time
scales of unprecedented accuracy and stability. It has also
facilitated the development of new atomic clock technologies,
which in turn will enhance the performance of GPS and future
GNSS systems.
This
talk will outline the principles and technology of modern
timekeeping and time dissemination, both internationally and
within Australia.
H-764GU EGI:
Upgrade Path for CNS/ATM and NAVWAR
Authors:
Brian E. Fly
and Joe Elchynski, Aircraft Systems Applications, Honeywell
Sensor and Guidance
The
H-764G Embedded GPS/INS (EGI) has been an enormously successful
product with over 70 different s/w adaptations (or
missionizations) currently flying and more missionizations under
development. When
the H-764G was first introduced in 1994, one important design
feature was the availability of spare card slots that could be
populated with additional functionality as technology advanced
or as new requirements were placed on the host platform.
That forethought has now borne fruit with the impending
changes to both the Military and the civil airspace environment.
Now, many DoD and industry leaders are in the throes of
determining how their current military systems will evolve to
allow operation within the Communication Navigation Surveillance
/ Air Traffic Management (CNS/ATM) airspace mandates that are
currently being levied. Key
elements of the CNS/ATM requirements are performance and safety. CNS/ATM will eventually result in an environment the FAA has
termed "free flight".
Free flight requires a shift in Air Traffic Control (ATC)
philosophy, from control to management.
Free flight creates a homogenous airspace that will
ultimately allow aircraft operators to select user preferred
flight plans saving time, money, and improving airspace use
efficiency. The
reality is that the environment is dramatically changing for
both the aircraft operators and the air traffic service
providers. No
operator is immune to these changes and those who desire to
continue operating in civil airspace will be required to be
compliant in terms of new procedures and supporting avionics .
In addition to CNS/ATM mandates, Military Aircraft will
need to consider the emerging NAVigation WARfare (NAVWAR)
requirements along with new Military GPS service changes.
NAVWAR is the localized denial of radio navigation
service to adversaries while maintaining a superior navigation
capability for ally forces in a theater of war.
In
many platforms, these new requirements/upgrades mean additional
avionics equipment in already over-crowded equipment bays and
cockpits. The spare
card slots in the H-764G unit provide an opportunity for these
platforms to adhere to CNS/ATM and NAVWAR mandates without
increasing LRUs and in some cases actually reducing overall
space claims for these technologies.
This paper will discuss Honeywell’s technical upgrade
path and the new capabilities of the H-764GU (U for Upgrade)
that will satisfy these requirements. CNS/ATM Features to be incorporated in the H-764GU include
the addition of Multi-Mode Receiver (MMR) functionality such as
VOR, ILS, Marker Beacon, and LAAS capabilities, along with
Navigation Management capabilities with associated Integrity
Monitoring for RNP area navigation.
Military features include a GPS receiver upgrade to
address NAVWAR and over-the-air- keying, along with Joint
Precision Approach & Landing System (JPALS) capabilities.
ADF Operational
Requirements and GPS Procurement Strategy
Author:
Jack Foley,
Aerospace Development Branch, Systems Avionics, Australia
The
advantages of being able to precisely coordinate many allied
force elements on land, sea and air are immense. When required,
force can be applied accurately with much less risk of
unnecessary harm. Accordingly, the ADF has become a major user
of GPS with several thousand units being brought into service.
However, the risk of interference is a major concern and this
has resulted in significant work in the field known as "NavigationWarfare".
The
Australian Defence Force is working with the US and UK on future
GPS development. The US is developing improved satellites which
will provide additional safety buffers against interference
sources. The three nations are jointly addressing means of
detecting and locating interference sources.
Also considerable work is being conducted within Defence
and by industry to minimise the vulnerability of GPS receivers
to interference.
ADF
GPS procurement to date has been concentrated in Joint Project
5195 which has sought to equip all major combatant elements with
military (P Code) GPS receivers. This project is now nearing the
end of its life having equipped a variety of land, sea and air
forces with GPS. Accordingly, studies are now underway to
determine the next generation of GPS for the ADF. Replacement
systems are planned to be procured throughout the latter half of
this decade under Joint Project 5408. Maximum use will be made
of improved GPS receiver and antenna design. For military
purposes, receivers will also be capable of operating on the new
M Code satellite signals and with the latest security modules.
Cellular
Network Technology - A Supplement or Competitor of GPS
Author:
Adam Game
Integrated
Space Geodetic Techniques for Monitoring Ground Subsidence Due
to Underground Mining
Linlin Ge and
Chris Rizos
School of
Geomatic Engineering, The University of New South Wales,
Australia
Mine
subsidence monitoring is of paramount importance in relation to the
safety and efficiency of mining operations. Moreover, in
established coal fields in eastern Australia, it has become
harder and harder to select underground minesites which can
avoid major engineering structures both on the surface and
underground (highways, bridges, buildings, abandoned workings of
old underground mines, and so on). Therefore, monitoring of
mining operations with the integration of several geodetic
techniques is also of crucial importance to the safety of the major engineering structures in the mining environment.
However, the current subsidence monitoring techniques are both
time-consuming and costly.
In
this paper, two schemes, namely, the integration of single- and
dual-frequency GPS receivers (the so-called ‘hard
densification’ option) and the integration of the
Continuously-operating Networks of GPS Receivers (CGPS) and
Interferometric Synthetic Aperture Radar (InSAR) (the so-called
‘soft densification’ option), are proposed to address the
applications of ground subsidence monitoring.
Continuously-operated
GPS networks consisting of dual-frequency receivers have been
established in many parts of the world. Among them, the GEONET
(GPS Earth Observation Network) operated by the Geographical
Survey Institute (GSI) of Japan, has evolved into the world’s
densest GPS network, with an average spatial resolution of 25km
and temporal resolution of 30 seconds (data sampling rate).
However, this spatial resolution is not high enough to
characterize the ground subsidence due to underground mining,
which usually only extends up to a few kilometres in extent.
Therefore, in the hard densification scheme, single-frequency
GPS receivers, which are much cheaper than their dual-frequency
counterparts, can be deployed to in-fill the CGPS network. The
dual-frequency measurements are used to generate
"error-correction terms", which are used in a linear
combination observation model for the processing of the
single-frequency measurements. In this way any GPS satellite
orbit bias and ionospheric delay can be largely eliminated, and
the tropospheric delay, multipath and observation noise can be
significantly reduced. Hence, it is feasible to obtain sub-cm
relative accuracy using this technique. Test results with four
single-frequency receivers will be presented.
In
the soft densification scheme, InSAR exhibits around 25m spatial
resolution. However, it is very sensitive to errors such as
atmospheric effects (tropospheric delay, ionospheric delay,
etc.), satellite orbit error, the condition of the ground
surface and temporal decorrelation. With the help of collocated
radar reflectors, CGPS measurements on the reference points in a
SAR image can be used not only to remove atmospheric effects but
also to mitigate the influence of the SAR satellite orbit errors
in InSAR results. Experiments at the Tower Colliery near Sydney,
Australia, will be described and results presented.
Modern Satellite Positioning Systems: Status, Applications
and Potential.
Authors:
Ramesh Govind,
John Dawson and Geoff Luton
Australian
Surveying and Land Information Group (AUSLIG)
The
Global Positioning System (GPS) is currently the most accessible
and accessed satellite positioning and navigation system
encompassing a wide range of applications and accuracies -- from
several metres for instantaneous navigation solutions to a few
millimetres for scientific studies of global and regional
geodynamics. Further
to its traditional positioning applications, the use of GPS for
high precision orbit determination of Low Earth Orbiting
satellites (LEOs) is growing. In addition to the GPS system, several other optical and
microwave satellite positioning systems for specific
applications are fully operational, under further development or
proposed. The current status, applications, products, opportunities and
potential of GPS LEOs, Satellite Laser Ranging, DORIS, GLONASS,
PRARE and Galileo are presented and discussed.
Definition
and Densification of the International Terrestrial Reference
Frame 2000
Authors:
Ramesh Govind, John Dawson and Geoff Luton.
Australian Surveying and Land Information Group (AUSLIG)
The
ITRF 2000 which is the latest in a series of modern global
terrestrial reference frames being implemented for satellite
positioning applications – providing an accurate set of
tracking station coordinates for determining satellite orbits,
earth orientation parameters, satellite and station clock
behaviour and the effects of the troposphere and ionsphere.
The ITRF2000 is initially defined in terms of its origin,
scale and orientation. This
has been achieved through the observation and analysis of global
SLR and VLBI data over a number of years.
The densification of the ITRF is achieved, in the main,
through global and regional GPS observations and data analysis.
AUSLIG has contributed to both the definition and the
densification of the ITRF.
Eight years of AUSLIG SLR solutions were submitted and
included in the definition of the origin and scale of the ITRF.
The SLR data, computation standards, solutions and
analysis are presented and discussed. Through their participation in a series regional GPS
campaigns under the auspices of the Asia Pacific Regional
Geodetic Project, Permanent Committee on GIS Infrastructure for
Asia Pacific (PCGIAP), UN Cartographic Conference since 1997,
AUSLIG and member countries have contributed to the
densification of the ITRF2000 in the region.
The data set observed and contributed by several member
countries – which defines the extent of the network, the GPS
computation standards, results and analysis of the submitted
solutions are presented and discussed.
GPS
Interference Mitigation and Localisation
Authors:
Doug Gray and
M. Trinkle
CSSIP,
University of Adelaide, Australia
GPS
systems are proliferating, particularly in aviation where the
FAA has decided it can be used for en-route navigation and CAT 1
non-precision landing approaches. The relatively low
interference power levels that can jam GPS receivers
necessitates the need to improve the system against either
intentional or unintentional interferences.
A
number of methods may be used to do so.
At a signal input level, the use of adaptive A/D
convertors may be used to prevent the digital receivers
saturating. Next,
adaptive filtering techniques using either single or multiple
element antennae coupled with both spatial and temporal digital
processors can be used to reject both narrrowband and broadband
interferences. Also other digital signal processing algorithms
can be used to reject specific interferences from a spread
spectrum system. Finally
at a systems level both GPS and INS receivers may be tightly or
loosely coupled to improve the accuracy and robustness of GPS in
the presence of jamming signals.
The
advantages and disadvantages of various generic implementations
of the above methods are reviewed and compared. The state of the
art in implementing some selected methods will be reviewed and
some experimental and simulation results presented to illustrate
key issues.
An
advantage of digital beamforming is that interference direction
of arrival information may readily be obtained from the antenna
arrays. Algorithms can be readily borrowed from the sonar and
radar fields to both calibrate such antenna and to estimate
interference location.
Joint Global
Positioning System Combat Effectiveness
Joint Test And
Evaluation (Jgpsce Jt&E)
Authors:
Colonel James R. (Bob) Greenlee and Lieutenant Colonel Dennis Lester
United States Air Force
SUMMARY:
The JGPSCE JT&E is a United States Department of Defense
test and evaluation program examining the vulnerabilities of US
joint warfighting operations to the loss or denial of GPS.
Through a series of field test events conducted from 2000
to 2003, the JGPSCE JT&E will investigate the impacts to US
joint operational missions employing precision engagement,
evaluate mitigations to those impacts, and demonstrate a
standardized methodology for GPS vulnerability testing in future
programs.
BACKGROUND:
The JGPSCE JT&E is one of ten active joint test and
evaluation efforts under the OSD JT&E Program.
JGPSCE was chartered in July 1999 by the Office of the
Undersecretary of Defense (OUSD), Director, Test, Systems
Engineering and Evaluation (currently Director, Strategic and
Tactical Systems, S&TS).
JGPSCE’s problem statement was derived from numerous
warfighter concerns: “Warfighters are increasingly reliant on
GPS. The impact of the loss or degradation of GPS capabilities
and the ability to operate despite that loss or degradation have
not been systematically tested or evaluated in a joint
operational environment.” To limit the scope of the effort and
to focus on the anticipated area of greatest vulnerability, the
JGPSCE team focused on the Joint Vision 2020 concept of
precision engagement and the specific missions of reconnaissance
and interdiction as the primary areas of JT&E investigation.
TEST
EVENTS:
JGPSCE plans to conduct four field test events during the course
of the JT&E. The first test, GYPSY ALPHA, is completed.
GYPSY ALPHA (conducted Fall 2000, White Sands Missile
Range New Mexico) was a tactical-level test examining ground
operations in a small-scale contingency scenario. Test GYPSY
BRAVO (Fall 2001, Yuma Arizona) will focus on air warfare in
partnership with the Marine Air Weapons and Tactics Squadron
One. Later tests
include GYPSY CHARLIE, examining the full tactical level of war
in Fleet Battle Experiment KILO, and GYPSY DELTA which will
examine the combined tactical and operational levels of war in
partnership with US Joint Forces Command.
SECURITY
CLASSIFICATION:
The presentation will be at the UNCLASSIFIED level. JGPSCE test results and details can be shared with UK and
Australian government representatives at the SECRET level under
the terms of the US-UK-AU Tripartite Agreement.
Centimetres For
Everyone:
Initial Results
From An Australian
Virtual
Reference Station Network Pilot Project
Authors:
Matthew
B Higgins, Queensland Dept of Natural Resources
Nicholas
Talbot, Trimble Navigation
The
Trimble Navigation, Virtual Reference Station (VRS) concept is
designed to support high-precision positioning over a wide area.
The system involves permanently running GPS base stations, at
spacings up to 70km, then feeding GPS data to a central
processing computer via a computer network. The central
processing facility then models spatial errors that limit GPS
accuracy. Corrections are then generated and made available for
roving receivers as required. VRS systems support a multitude of
positioning applications and enable roving receivers to be
positioned anywhere inside the network with an accuracy better
than a few centimetres in real time. The concept is an extension
of the so-called real time
kinematic (RTK) technique developed for GPS surveying and
other forms of high precision positioning. VRS overcomes three
main limitations of the current RTK technique. Firstly,
operators no longer need to establish and run their own base GPS
receiver and base radio every time they want to work. Secondly,
the use of mobile phone technology overcomes the limitation of
the range of radio communications. Thirdly, multiple base
stations increase the redundancy and thus the confidence in the
resulting rover positions.
A
pilot network has been established over southeast Queensland as
a partnership between the Queensland Department of Natural
Resources (DNR), Trimble Navigation and Ultimate Positioning.
The pilot network is the first of its kind in the southern
hemisphere and capitalises on existing infrastructure using four
DNR offices and the computer network linking them and on DNR’s
existing GPS equipment and expertise. This paper presents
initial results from an investigation of the technical and
financial feasibility of a VRS network.
Real Time
Kinematic GPS surveying for Queensland Rail’s Railway Surveys.
Authors:
James Hunt,
Geoffery Devaney, Roger Van Cronenburg, Derek Stanmore
Queensland
Rail, Australia
GPS
has been in use for real-time, high precision kinematic
applications for some years.
Queensland Rail (QR) uses high precision measurement of
its rails to facilitate track maintenance operations.
QR recognised the potential for RTK techniques to replace
its existing ‘conventional’ surveying methods.
In
1999 QR developed a GPS Surveying ‘trolley’ that used RTK to
precisely survey its rail centreline at speeds of up to 20 k/h.
The trolley has been designed with spring loaded wheels
to maintain a fixed alignment with one rail.
Verticality of the GPS antenna is maintained by a
pendulum and pneumatic rams.
The
trolley has been used to successfully survey several hundred
kilometres of railway line.
The use of a vehicle constrained to fixed rails has
allowed observations to be repeated under varied conditions and
for the results to be compared to rapid static GPS surveys and
total station observations.
From the data generated QR has been able to draw some
conclusions on the accuracy and repeatability of RTK surveys.
Combining GPS,
INS, GIS and Video Technology to provide Rapid Railway Asset
Mapping.
Authors:
James Hunt,
Geoffery Devaney, Roger Van Cronenburg, Derek Stanmore
Queensland
Rail, Australia
Queensland
Rail’s Survey Section has the responsibility for identifying
the location of QR’s major assets.
Primary among these are the rail line itself and it’s
associated signals, signs, electrical fittings and other rail
corridor furniture. The
maintenance of a data set representing the location of assets
along 10 500 Km is a major task.
In the past, QR (and many other organisations) have found
this task impossible to undertake in a cost effective manner.
Increased use of GPS for Train locations, third party
operators on Queensland’s rail lines and better data
management tools have dictated that the asset location dataset
must be accurate and reliable.
The
“Automated Track Survey and Mapping System” (ATS&MS)
project provides Queensland Rail with a system to capture,
manage and make available to users, location data on all its
rail corridor assets. Data
capture is undertaken using a digital video photogrammetry
process developed by Geomatic Technologies.
In the field data is captured on the rails using a
vehicle fitted with GPS, INS and digital video cameras.
In the office the GPS, INS and video data is used to
allow a photogrammetric extraction of the location of any asset
within the rail corridor.
Data
management is achieved using Microsoft SQL Server DBMS for
tabular data and ESRI’s ArcInfo for spatial data.
ESRI’s ArcView and ArcView IMS make the data available
to users and allows for the development of spatial information
systems utilising the data.
GPS
and the Australian Height Datum
Authors:
Gary Johnston
& Geoff Luton
Australian
Surveying and Land Information Group (AUSLIG)
GPS
produces height as well horizontal position, but the height is
referred to an ellipsoid, rather than the mean sea level
commonly used for heights. These ellipsoidal heights can be
simply reduced to the geoid (an equipotential surface that is
approximated by mean sea level) by subtracting the separation
between the geoid and the ellipsoid. There have been a number of
continually improving Australian models of this separation
(AUSGeoid91, AUSGeoid93 and AUSGeoid98). However, the geoid does
not coincide exactly with the mean sea level height datum used
in Australia.
Since
1971, Australian heights have been referred to the Australian
Height Datum (AHD) that is based on a limited mean sea level
determination at thirty two tide gauges around the continent. A
comparison of accurately determined ellipsoidal and AHD heights
at these original sites has revealed a north-south slope of
almost a metre between the geoid and AHD.
Where differential GPS techniques are used this
difference largely cancels out, resulting in accurate
differences in AHD height from GPS baselines, but where a single
accurate GPS height is reduced using AUSGeoid, it can be
significantly different from the equivalent AHD value.
An
ongoing campaign is underway to determine additional, accurate
ellipsoidal heights at major AHD sites away from the coast, to
provide more detail on the relationship between the geoid and
AHD. This paper presents the results obtained so far and
discusses the potential for obtaining more accurate heighting
from GPS and a better understanding of the accuracy of the
Australian Height Datum.
This
paper carries out a comparative performance analysis of
integration algorithms for navigation using global positioning
systems (GPS) and inertial navigation systems (INS) when GPS is
subject to intentional or unintentional interference.
The effect of interference on GPS measurements is
modelled as Gaussian additive noise, thus interference level is
assumed to be low enough so that GPS is still operating, but
high enough to degrade the
quality of GPS. The paper investigates some of the existing
centralised and decentralised GPS/INS integration algorithms
such as the ones described in (Brown & Hwang 1997). The
performance of these algorithms is analysed via Monte Carlo
simulation studies using a Matlab/Simulink software package
developed by the authors.
Among
different integration architectures, the simulation results
indicate that the centralised integration algorithm, based on
the complementary Kalman filtering, outperforms the
decentralised ones when there is no interference. However, in
the presence of GPS interference, one of the decentralised
integration algorithms seems to be more robust
than the others. During
simulations, it has been observed that the model mismatch due to
interference may cause filter divergence.
This
paper demonstrates that the GPS performance
can be improved significantly by integrating it with an
INS when it is subject to interference.
Reference:
Brown,
R.G. & Hwang P.Y. (1997), Introduction
to Random Signals and Applied Kalman Filtering, John Wiley
& Sons, Inc.
Positioning And
Timing Services -
An Integrated Infrastructure View
Authors:
Donald
Latterman and Daniel P. Martens,
Science Applications International Corporation (SAIC),
USA
All
current national or regional precise positioning and timing
programs tend to take a program-centered view of the
user’s needs rather than taking a service perspective.
Program efforts are focused on improving the capability of a
single system not on building an overall level of service. With
a focus on space-based systems as solutions, rather than
addressing a precise positioning and timing service, other (non
space-based) solutions and/or augmentations have not been
adequately considered in architecture design trades.
Additionally, they have tended to view each national or regional
system as the solution to all needs rather than as an integral
part of a global system. This paper starts from a
“global stewardship” perspective of an
integrated set of national and regional systems to provide an
efficient and effective solution to users’ precise
positioning and timing needs. It evaluates which categories of
needs are best satisfied by global space systems, regional space
and non space-based systems, and/or local non-space systems. It
further looks at developing a candidate integrated architecture
and allocating performance requirements. The paper concludes
with a set of recommendations to explore future integrated
architecture approaches that meet the user’s needs for
precise positioning and timing services.
GPS as a Global Time Standard
Proposed Enhancements in Time Keeping & Dissemination
Authors:
Judah
Levine and Al Gifford, NIST
Scott
Pace, RAND Corporation
Jules
McNeff, SAIC
Tom
Bartholomew, TASC
On
1 May 2000, the White House issued a Presidential directive
requiring the Global Positioning System (GPS) turn off Selective
Availability (SA) on 2 May 2000. This action has enabled an
enormous improvement in GPS time transfer performance.
It allows current Standard Positioning Service (SPS)
civil users to attain time transfer accuracies here-to-fore only
available to authorized Precise Positioning System (PPS) users.
The directive also sets the stage for potential expanded
future services which could include real-time dissemination of
international civil time references via GPS III. A number of recent U.S. Presidential and Congressional
mandates, actively promoting GPS as a global time source,
guarantee continued access of high quality time services to the
international civilian sector.
The
paper provides, as a baseline, a comparative analysis of civil
GPS SPS direct time transfer performance both before and since 2
May 2000. The SPS
data presented is compared with time recovered by the United
States Department of Defence (USDOD) at the United States Naval
Observatory (USNO) in Washington DC. The USNO monitors and provides data for steering GPS time
using data from authorized PPS GPS time transfer receivers.
This
paper will discuss a proposed architecture for the real-time
dissemination of an internationally derived estimate of UTC via
GPS III. The
information content basis for this proposed new service is the
current “Circular T” publication from the Bureau
Internationale de Poids et Mesures (BIPM).
By broadcasting these estimated offsets and rates, GPS
III could provide a real-time estimate of UTC to civil users
globally.
For
PPS users that may be concerned about the integrity and/or
interoperability of their systems if UTC(GPS) is estimated
directly from non-USDOD sources,
this paper discusses techniques for validating GPS time
transfer products. These
techniques, along with the continued management of GPS system
time by the USDOD, will guarantee the information security (INFOSEC)
aspects of USDOD time keeping while maintaining and providing
civil users with continuing high quality time products.
This
paper concludes with a description of a method of integrating
the techniques described above in an operational environment
which strengthen GPS as a globally available common time
reference. In
addition, a brief discussion of potential Galileo
interoperability issues will be addressed.
Operation
of the US DoD GPS Support Center
Authors:
Joe Lortie and
Gary Barrett, Overlook Systems, USA
In
June 1999, United States Space Command (USSPACECOM) took formal
steps to stand up a support center for military and government
Global Positioning System (GPS) users worldwide.
The Center was created to meet three main objectives:
1.
Detect,
Analyze, Report And Facilitate Resolution Of GPS Anomalies
2.
Monitor
And Report GPS Performance
3.
Provide
GPS Status, Constellation Status, And Tactical Support
This presentation will outline the functions of the
GPS Support Center (GSC) and discuss analytic products and
services.
Creation
of the GPS Support Center
US Space Command is
the official Department of Defense (DoD) focal point for all
military operational space systems, including GPS.
Annex 3 of the Memorandum of Agreement (MOA) between the
DoD and the Department of Transportation (DOT) establishes US
Space Command as the DoD focal point for all GPS service
disruptions.
Numerous military and civil issues
highlighted the immediate need for a single, consolidated GPS
Support Center. In
response to these issues, the Secretary of Defense tasked the
Commander in Chief of US Space Command, to “establish a (GPS)
reporting and resolution process”.
Overlook Systems Technologies is responsible
for the daily operation of the GPS Support Center under
operational tasking by the Second Space Operations Squadron.
Support
Center Tasking
The mission of the GPS Support Center is to:
1.
Facilitate Resolution Of GPS Service Disruptions
2.
Facilitate Resolution Of User Equipment Problems
3.
Maintain The DoD GPS Problem Report Database
4.
Monitor GPS System Level Performance
·
Assure Compliance With Military And Civil
Directives
5.
Provide Tactical Support To Military Forces
·
Exploitation Of GPS In Mission Planning
·
Assessments Of GPS Mission Effectiveness
As
the DoD’s focal point for GPS operational matters, the GSC
serves as the US Space Command’s interface with the civilian
community. The military-civil interface is established through
the United States Coast Guard’s (USCG) Navigation Center (NAVCEN)
and the Federal Aviation Administration’s (FAA) National
Operations Control Center (NOCC).
Requests from the civilian community that require GPS
performance analysis or additional information are forwarded
from the NAVCEN to the GSC.
GPS
Support Center Products and Services
Detect, Analyze, Report and Facilitate
the Resolution Of GPS Anomalies
In order to manage
reported anomalies properly, the GSC maintains a problem
reporting database. This
gives the GSC the ability to correlate problem reports that may
have common causes, identify possible reasons for reported
problems and to identify the best agent to work the problem.
This single repository for GPS anomaly information allows
the GSC analysts to quickly coordinate anomaly investigation
efforts and assist U.S. Space Command in assessing the scope and
ramification of the anomaly.
Overlook
Systems Technology has developed the software tools necessary to
conduct analysis and GPS performance prediction.
Monitor and Report GPS Performance
This
objective provides the GSC with the role of routinely
collecting, analyzing and reporting PPS performance on a global
basis and developing the capability to produce regional
assessments of the Standard Positioning Service (SPS).
Several reasons are given for providing these
capabilities:
1)
Performance trends can point out possible long-term
performance problems
2)
Raw performance data provides a point-of-departure for
analyzing problem reports and removing possible candidate causes
from consideration
3)
Routine
performance reporting provides military decision makers with
better information on which to base operational decisions
Monitoring
and reporting requires the continuous collection of raw data
from the GPS Control Segment and processing the data to generate
global Precise Positioning Service (PPS) assessments.
Assessments for range, position and time parameters are
routinely provided via the GSC’s classified and unclassified
websites.
Another key piece of the performance assessment
puzzle is the characterization of GPS PPS receiver performance,
to include acquisition, satellite selection strategies, thermal
noise behaviors and cryptography implementation.
This information is used in conjunction with OCS data to
estimate total PPS position and time error from a user’s
perspective.
Provide GPS
Status, Constellation Status, and Tactical Support
·
The
GSC uses various means to provide GPS status, satellite
constellation status and tactical support to the user
communities so they can conduct mission operations.
The GSC provides a number of standard products and
services, such as periodic reports, updated Web page content,
and specific tactical support.
All reports incorporate planned and actual satellite
outages and orbit changes
The
products reflect the intent set forth in Annex 3 of the MOA
between the DoD and the DOT and meet the prevalent need for GPS
support to military and government users.
SHIPBORNE
AUTOMATIC IDENTIFICATION SYSTEM (AIS)
Author:
John Macdonald,
Navigational Services, Australian Maritime Safety Authority
The
concept of a shipborne “transponder” developed out of a
perceived need for enhanced information transfer between ships
and shore in order to identify vessels and improve the
efficiency and safety of shipping traffic movement. This initial focus on ship to shore data exchange has
subsequently expanded to encompass the additional requirement
for ship-to-ship data transfer to assist in collision avoidance.
In
the same timeframe, the modern revolution in navigation and
information technologies has provided the capability and the
solution to these emerging requirements.
Combining satellite based positioning and timing systems
(GPS/DGPS), electronic charting, communications and open
information systems architecture, the maritime electronic
industry can now provide working prototypes of what is known as
the Universal Shipborne Automatic Identification System (AIS).
AIS
equipment is to be implemented as a mandatory carriage
requirement for all ships over 300gross tonnage on international
voyages, commencing with newly constructed ships from 1 July
2002 and progressively other types and sizes of ships up to 1
July 2008.
This
paper addresses the internationally endorsed operational and
functional requirements of AIS and its performance and technical
standards. It also
examines current international activity in the application of
AIS technology including Australian preparations for its
implementation in our waters.
Instant RTKTM
– No More Waiting
Author:
Roderick
MacLeod, SAGEM Australasia Pty Ltd
Commercial development of real time kinematic systems to
provide centimetre level accuracies, began in the early
1990’s. Since then the major issue has been the time it takes
these systems to get to this accuracy. The process is called
initialisation and is where a computation in the receiver is
required to fix the carrier wave ambiguities to integers, also
known as a “fixed solution”. In this period the receiver
cannot be used for precise positioning. Early systems required
the receiver to be stationary or on a known point. While there
have been enhancements made such as “on the fly”
initialisation, where the receiver can be in motion, there still
remains a significant time to find the fixed solution, which has
limited the usage in areas such as general surveying and
precision machine control. Now this has been solved using an
enhanced receiver design and new algorithms that provide
initialisation in less than 5 seconds at the 99.9% confidence
level. This paper discusses this Instant RTKTM
technology within the new Ashtech Z-Xtreme receiver and
highlights the benefits users can now expect.
Multimodal
Application of GNSS Augmentation
Author:
Keith
McPherson, Airservices Australia
The
use of GNSS is growing exponentially, with new applications
occurring regularly. In
many instances there is duplicity of effort in fielding new
applications. An example is the multitude of differential GPS services
being offered, not only in Australia, but also around the world.
Harnessing this duplicity is more efficient.
Different providers all use the same core technology.
It is in the processing, application and broadcasting of
differential signals where the products vary.
If the core technology is common, each provider would
potentially save on investment by multiple sharing of the core
information. This
paper identifies potential multimodal applications of GPS in
Australia with respect to GPS augmentations.
Status of ICAO
GNSS Standards and Recommended Practices
Author:
Keith W.
McPherson, Airservices Australia
The
International Civil Aviation Organisation (will) approved the
Standards and Recommended Practices for the use of GPS for civil
aviation in March 2001. The
Applicability Date is 1 November 2001.
The approvals included GPS, GLONASS, Ground Based
Augmentation Systems (Category 1) for precision approaches,
Space Based Augmentation Systems (SBAS) for wide area
navigation, Aircraft Based Augmentation Systems (ABAS) and the
GLONASS signal in space. This
paper discusses the elements of the approvals and the
ramifications of the approvals, including legal and
institutional issues.
GNSS Regional
Augmentation Systems in Asia Pacific
Authors:
Keith W.
McPherson, William S. Ely, Joy M. Stewart, Graeme K. Crosby
Airservices
Australia
Satellite
augmentation systems are being implemented around the world to
overcome the deficiencies of raw satellite navigation position
data. This paper
discusses the augmentation systems likely to have an impact on
Australia and the legal and institutional issues associated with
them. The systems
include the US Wide Area Augmentation System, (WAAS), the
Japanese MT SAT Augmentation System (MSAS), the Chinese wide
area differential GPS system, the Australia Ground based
Regional Augmentation System (GRAS) and the precision approach
Ground Based Augmentation Systems (GBAS) for Category 1
precision approaches.
Emerging
positioning technologies and nascent electronic commerce
business models within the information economy, their influence
on Land Victoria's Geodetic Strategy and relevance to the
Spatial Data Infrastructure.
Authors:
James Millner,
Martin Hale and Peter Ramm
Land Victoria,
Department of Natural Resources, Australia
Jessica Smith,
Neil Brown, Allison Kealy and Francisco Escobar
Department of
Geomatics, University of Melbourne, Australia
As
custodians of Victoria's Geodetic Infrastructure, the Land
Information Group has certain rights and responsibilities for
managing information on behalf of the community. The principles
of custodianship define appropriate standards regarding data
content, collection, conversion, maintenance and access to
geodetic information. These principles are developed in
consultation with government, academia, industry groups and the
user community. Justification for these custodian activities is
contingent on the creation of a strategy that can maximise the
utility of the Geodetic Infrastructure.
Convergence
of positioning systems, information technology and their
confluence with emerging wireless communication equipment, has
facilitated the development of various electronic commerce
business models within the information economy. Recently, many
electronic commerce (e-commerce) business propositions such as
Location commerce (L-commerce), Position commerce (P-commerce)
and e-location services have emerged. In addition, a variety of
platforms have been established to service these electronic
markets including Business to Business (B2B) and Business to
Government (B2G) e-markets, Application Service Providers (ASP)
and Telematics Bureaus. The influence of emerging technologies,
new business enterprises and various electronic markets on Land
Victoria's Geodetic strategy is examined and discussed. A Government to Business (G2B)
e-strategy, relevant to the Spatial Data Infrastructure, with
particular reference to Victoria's state-wide positioning
network GPSnet is discussed.
Wireless
Mapping and Guidance Services
Author:
Kirk
Mitchell, Webraska Mobile Technologies, Australia
The
advent of the Wireless Application Protocol (WAP), and other
such network based technologies, has meant that map publishers
can now migrate Internet mapping services from the desktop to
handheld devices. The ability to integrate positioning
information within such services adds considerable value to the
overall end user experience.
Webraska
Mobile Technologies is the world's first provider of navigation,
traffic information and maps delivered as packaged services to
consumers using Internet enabled phones. Webraska's services
were launched in early 1999 to France’s SFR mobile
subscribers. Since this initial offering, Webraska services have
expanded to include a global offering accessed by numerous
wireless carriers and portals. This paper details Webraska’s
offering and explores various issues related to delivering
location based mapping and guidance services and the
opportunities associated with incorporating GPS within such
services.
Applications
using combined GPS, GSM and GIS Technologies for the Automotive
Industry
Author
Trevor Mogg,
Managing Director, MaxiTrak Pty Ltd (a subsidiary of Compucat
Research Pty Limited), Canberra, Australia
Over
recent years, advances in wireless communications technology
such as GPS and GSM have led to the widespread availability of
low cost, high performance Automatic Vehicle Location (AVL) and
mobile data systems.
The
combination of these two technologies provide features and
benefits in a wide range of applications, and when combined with
a Geographic Information System (GIS), the potential
applications are enormous.
MaxiTrak
specialises in the design and development of innovative vehicle
management and information systems using these and other
complimentary technologies.
High
Precision Dynamic GPS System For On-Line Structural Monitoring
Authors:
Clement
Ogaja, Chris Rizos and Jinling Wang
Satellite
Navigation and Positioning Group, School
of Geomatic Engineering, University of New South Wales,
Australia
James
Brownjohn,
School of Civil and Structural Engineering, Nanyang
Technological University, Singapore
A monitoring project in Singapore is described,
in which an RTK GPS system is used to generate time series of
antenna positionsfor monitoring the behaviour of a high rise
building. A pair of Leica GPS receivers have been installed on the
building since the start of 2001.
The RTK solutions are automatically recorded and
analysed. This system will contribute to a project of monitoring that
commenced in 1995 with the installation of two pairs of
accelerometers and two UVW anemometers.
The
aim of this project is to capture the building loading and
dynamic response during strong winds and remote earthquakes to
aid local design code development.
The GPS monitoring
system installed on the Republic Plaza building (at 280m, the
maximum height of any Singapore building) generates on-line
antenna coordinate measurements.
These will complement and corroborate the
acceleration data to provide the complete picture of the
building displacement across the full spectrum of loading
frequencies, allowing for direct estimation of lateral loads.
The system design and installation is described, as well as the method of
time series analysis that is being investigated. Initial results are presented to demonstrate the feasibility
of using high precision GPS techniques to monitor high frequency
movements.
Air
Navigation
Author:
Professor
Brian O'Keeffe AO,
FANS PLANS P/L, Australia
Satellite
navigation has become the great utility for aviation. Fortunately, it became available at the time in the early
1980’s when the aviation community came to recognise the
increasing limitations of the existing navigation systems and
that new systems would be needed to take aviation into the 21st
century. Satnav was
indeed the tool for which aviation had been searching to provide
navigation services on a global scale for present and future
requirements. The
ICAO Future Air Navigation Systems (FANS) Committee was thus
able to integrate satnav in the concept of the new
Communications, Navigation, Surveillance and Air Traffic
Management (CNS/ATM) system.
From these beginnings, satnav has been eagerly embraced
by the aviation industry for en-route, terminal area,
non-precision and precision approach operations.
In 1995, the “FANS1 package” was certificated for the
Boeing 747-400 to meet a navigation accuracy of 4 NM (now 1 NM)
and non-precision approaches down to 250 feet using GPS as an
essential component of the on-board navigation system.
The B-777 was the first aircraft to be designed to
incorporate satellite navigation.
Similar systems are now available for other aircraft.
As a result, new air routes have been opened up and
operations for all aircraft have been greatly expanded.
The satnav picture has grown steadily brighter.
The GPS constellation has grown from 18 to more than 24
satellites and an independent system –Galileo- has been
proposed by Europe. Aircraft-based,
ground-based and space-based augmentation systems have been
developed or are in being developed and some are in everyday
commercial operation. All
these developments mean the aviation operations will continue to
be enhanced and satnav will be an essential part of aviation
operations in the 21st century.
GNSS – One
State’s Perspective
Author:
Peter
Ramm, Geodetic Infrastructure, Land Victoria, Australia
This
presentation will provide one State’s perspective on GNSS.
It will highlight the value in coordination of the
provision of infrastructure and the benefits of working
cooperatively with other GNSS players.
The Victorian GPSnet will be used as a case study. GPSnet is a network of GPS base stations and has been
established through partnerships with a range of industry
players. The
breadth of the LV partner’s businesses gives an indication of
the potential for this type of technology.
A view of potential future developments of GPSnet will
also be given.
The
AGCC plays an important national role in GNSS. Victoria has recently established a State Reference
group to both support the role of the AGCC and to provide input
to State programs such as GPSnet.
The early experience with this group together with its
potential contribution will also be discussed.
Some
GNNS issues identified from a State perspective will also be
discussed. These
may also have wider application.
Precise GPS
Positioning: Prospects and Challenges
Author:
Chris Rizos,
School of Geomatic Engineering, The University of New South
Wales, Australia
Carrier
phase-based GPS positioning is now an indispensible tool for a
wide range of precise applications in navigation, surveying and
geodesy. To address
such a variety of applications, many implementations of precise
GPS techniques have been developed.
Almost all techniques involve 'relative' positioning, in
which one GPS receiver/antenna's coordinates are determined with
the aid of measurements also made at a stationary base or
reference receiver. In
essence all of these techniques may be categorised according to
a small number of attributes: is the technique implemented in
the post-processed or real-time mode? does the scenario involve
static or kinematic positioning? is the inter-receiver distance
comparatively short (say <10km) or very long (e.g.
>1000km)? is a single base station involved or a reference
network of receivers? and so on.
Each of these attributes also determines the data
processing strategies that should be employed to ensure accurate
and reliable positioning results.
Over the last two decades 'precise GPS positioning' has
played a role similar to F1 racing.
That is, challenges to carrier phase-based GPS
positioning spur research on new hardware, new data processing
algorithms and new operational procedures.
In this paper, the challenges, progress and outlook for
high precision GPS positioning will be discussed, with
particular emphasis on identifying the constraints
and commenting on the prospects for addressing them in the near
and medium term.
Mitigating
Differential Troposphere Effects for GPS-Based Volcano
Monitoring
Authors:
Craig Roberts
and Chris Rizos, Satellite Navigation & Positioning Group,
School of Geomatic Engineering, The University of New South
Wales, Australia
The
UNSW designed low-cost GPS volcano monitoring system installed
on Gunung Papandayan seeks to characterise the ground
deformation within the volcanic edifice. Hourly baseline
solutions produce a time series of data designed to detect any
ground motion. Differential tropospheric effects between GPS
receivers separated by a large change in height (in this case up
to 1400m) impact on the quality of this time series data,
particularly in the case of the vertical component. This
increased variability constrains reliable ground deformation
detection to the decimetre level. The Saastamoinen troposphere
model is recommended as the most suitable to account for the
hydrostatic (dry) part of the delay. The residual wet zenith
delay, as well as any remaining effects due to the differential
troposphere (not accounted for using existing models), is
estimated as an additional parameter in the baseline solution.
Existing approaches to parameter estimation do not consider the
height difference between GPS receivers. The functional model
proposed in this paper seeks to address this shortcoming. GPS
baseline processing is more of a challenge in this case due to
the short session length and reduced number of observations from
a single-frequency-only system. Single-frequency data from the
SAGE (New Zealand), SCIGN (southern California) and GSI (Japan)
networks are used to demonstrate improvements using this
approach.
Evaluation of
the European GPS Navigation Overlay System using the Satellite
Navigation Avionics Package
Authors:
Tom Sanders,
ARINC Inc; Todd Lardy, US Navy; Steve Leighton, David Harriman,
UK NATS
Within
the International Civil Aviation Organization (ICAO) member
states, the development of Global Navigation Satellite System (GNSS)
is being standardized to support global navigation requirements.
The United Kingdom’s National Air Traffic Services (NATS) is
tasked to support the UK's implementation of GNSS; specifically
the development of augmentation services for the Global
Positioning System (GPS). ICAO is standardizing on two different
types of GNSS augmentations – Ground Based Augmentation
Systems (GBAS) and Space Based Augmentation Systems (SBAS).
Within the United States, the Federal Aviation Administration (FAA)
is pursuing development of SBAS and GBAS systems known as the
Wide Area Augmentation System (WAAS) and Local Area Augmentation
System (LAAS), respectively.
Similarly, the European community is developing an
augmentation system similar to the US WAAS known as the European
GPS Navigation Overlay System (EGNOS).
The
NATS and Naval Air Warfare Center-Aircraft Division (NAWCAD) are
cooperatively evaluating GNSS augmentations and promoting their
interoperability. To facilitate this evaluation, a series of flight
demonstrations will be performed throughout the UK during the
summer of 2000. The
demonstrations will be accomplished using the SBAS Navigation
Avionics Package (SNAP), consisting of the WAAS Verification
Receiver, a WAAS Gamma control head and a PC-104 interface
device. SNAP was previously used to assist in evaluation of the
WAAS SIS. The SNAP
was developed by NAWCAD for evaluating the WAAS and will be used
in this effort to show interoperability of international SBAS
signals. NATS will install SNAP into a civil aircraft and fly a
variety of profiles to demonstrate the utility of European
Geostationary Navigation Overlay System (EGNOS) to the UK
aviation community. Both
parties will gain valuable experience ensuring compatibility
between U.S. and European Satellite Based Augmentation Systems.
GPS
Analysis with the Aid of Wavelets
Authors:
Chalermchon Satirapod, Clement Ogaja, Jinling Wang
and Chris Rizos
School
of Geomatic Engineering, The University of New South Wales,
Australia
The
classical least-squares processing of GPS measurements generates
residuals, which contains the signature of both unmodelled
systematic biases and random measurement noise. It is desirable
to separate (or minimise) the systematic biases contained within
the GPS measurements. This would be relatively straightforward
if there were some apriori knowledge of the phenomena related to
these errors. Common ways of dealing with this problem include (i)
changes to the stochastic modelling, and (ii) redefinition of
the functional model.
In
this study, we apply a method based on the use of Wavelets to
decompose GPS double-differenced (ambiguity-fixed) residuals
into a low-frequency bias and a high-frequency noise term. The
extracted bias component is then applied directly to the GPS
measurements to correct for this term. The remaining terms,
largely characterised by the GPS range measurements and
high-frequency measurement noise, are expected to give the best
linear unbiased solutions from a least-squares process. A robust
VCV estimation, using the MINQUE procedure, controls the
formulation of the stochastic model. This method can be applied
to a variety of static and kinematic positioning applications.
Australian
Strategies for GNSS Application:
the Role of the
Australian GNSS Coordination Committee (AGCC)
Author:
Professor Don Sinnott, Chairman, Australian GNSS
Coordination Committee
On
26 May 200 the Deputy Prime Minister and Minister for Transport
and Regional Services, the Hon John Anderson MP, announced the
establishment of the Australian GNSS Coordination Committee (AGCC).
This announcement represented both the conclusion of an
intensive consultative effort by an interim committee that
developed a business case for the AGCC and a beginning for the
permanent AGCC, which set about its business soon after the
Ministerial announcement.
The
impetus for the AGCC comes from a recognition of the growing
importance of GNSS to our national life.
Many forms of navigation, position fixing and timing now
have significant reliance on GNSS.
The benefits as well as the dependencies are growing at a
remarkable rate. The
essentially free-market way GNSS is penetrating our national
life in business and recreation has delivered great benefits at
modest cost but there are important underpinning national issues
to be addressed. These
include the following.
·
Can
Australia enhance its national benefit by capitalising on GNSS
opportunities in a more coordinated way?
·
Are
our international relationships with GNSS providers serving the
nation to best effect?
·
Are
GNSS vulnerabilities, dependencies and legal implications
appreciated and understood?
·
Are
there some regulatory issues, including spectrum management, to
be addressed arising from the pervasive application of GNSS?
·
Is
the evolving national balance between government-provided and
market-driven GNSS augmentation services appropriate?
This
paper will address these questions in the context of the ongoing
program of the AGCC.
Time
Synchronisation For Indian WAAS Technology Demonstration System
Author:
M.R.Sivaraman,
Systems & Applications Group, Space Applications Centre,
India
Indian
Space Research Organisation (ISRO) is planning a Technology
demonstration of Wide Area Augmentation System (WAAS) over
Indian Ocean Region (IOR), in collaboration with Airport
Authority of India (AAI). One of the main requirements for this
technology demonstration is time synchronisation between Range
& Integrity Monitoring Stations (RIMS), Master Control
Centre (MCC) & Navigation Land Earth Station (NLES) to a
Local Network time and also between the Local Network Time and
GPS Time, maintained by US Naval Observtory. There are basically
two techniques for this time synchronisation viz. (1) Two Way
Satellite Time & Frequency Transfer Technique
(TWSTFT) and (2) GPS Common View Time Transfer
Technique. We, at Space Applications Centre,
Ahmedabad, carried out a Time Synchronisation Experiment between Ahmedabad and Delhi, using TWSTFT
Technique and INSAT 3B satellite. Using TWSTFT
Technique, we have demonstrated a time transfer accuracy
of 1 ns. This can meet the requirements of Indian WAAS
Technology Demonstration System and will be used by us for
Technology Demonstration of WAAS over Indian Ocean Region. We
have also demonstrated a frequency transfer accuracy better than
1X10E-12 using TWSTFT. In this paper, we present the details of
the experiment and discuss the results (both time transfer &
frequency transfer) obtained. We will also try out soon, GPS
Common View Time Transfer Technique and compare its performance
with simultaneous TWSTFT. The preliminary results of this
experiment will be also discussed in this paper.
Assessing
Spatial Data Infrastructure Architecture for Integration with
Wireless Location Services
Authors:
Jessica Smith,
Allison Kealy and Professor Ian Williamson
Department of
Geomatics, University of Melbourne, Australia
Spatial
Data Infrastructures (SDIs) have been identified as a mechanism
through which complete and consistent spatial data sets can be
accessed and retrieved. Whilst SDIs have been developing,
wireless communication technologies have been undergoing a rapid
evolution. The convergence of wireless communications,
positioning technology and SDIs are providing new facilities,
new applications and as a result, new challenges for spatial
data providers and users.
To
capitalise on the opportunities presented through the merger of
these key areas, the design of SDIs may require modification.
Naturally, different applications will have different spatial
data requirements, however it is envisaged that there will be
common infrastructure requirements (such as query and delivery
mechanisms) that will be applicable for a range of wireless
applications.
One
of the most important issues in relation to delivering
information to wireless users is that of data currency. It is
imperative that a mobile user be provided with accurate, up to
date data. Whilst this is also an important issue for non-mobile
users, it is significantly important for users ‘on the
move’. Thus rather than individual organisations duplicating
and maintaining data sets, providing access through a standard
SDI would be most beneficial.
Infrastructure requirements for Australian wireless applications that
utilise spatial information will be determined through the
development of a personal navigation system for the visually
impaired. The accuracy and reliability requirements of a
navigation solution for a visually impaired person are much
greater than for a sighted person, thus the rigour of the data
content and delivery methods is of paramount importance. A
preliminary review of the requirements
of such a system linked to an SDI will be examined in this
paper.
Title:
GPS in Public Safety Communications
Author:
Geoff Spring
The ARIES Satellite Project - an Overview
Author:
Dr Ted
Stapinski, CSIRO, Canberra, Australia
ARIES
is a satellite concept. Its genesis was in work done by CSIRO
Division of Exploration and Mining over a period of 20 years and
by Auspace on lightsat technology in the last decade. The Phase
A space segment study looked at user requirements with
representatives of the mining community, who provided 75% of the
study funding. The spacecraft consists of a 3-axis stabilised
platform and an instrument payload consisting of a large
telescope, two spectrographs, a Panchromatic high resolution
sensor, and visible and infrared focal planes, and control and
data handling electronics. Electronic design issues included low
noise, high speed focal planes, high rate data handling and
formatting, mass solid-state storage, high-rate X band downlink,
and trade-offs within this chain.
ARIES
instrumentation is to be designed and built in Australia and
mated to a commercially procured platform prior to launch on a
Russian or US rocket. Dr Ted Stapinski is the founding Managing
Director of Auspace.
The
Implementation of GPS in Field Robotics
Author:
Dr. Salah Sukkarieh, Australian Centre for Field
Robotics, University of Sydney, Australia
Over
the past seven years, the Australian Centre for Field Robotics (ACFR)
has been developing high integrity navigation (and control)
systems for field applications including mining, agriculture,
forestry, construction, cargo handling, and sea.
The
predominant navigation system developed has been the
implementation of an Inertial Navigation System (INS) aided by
GPS.
This
paper will discuss the major research areas underway at the ACFR,
which include:
o
The
development of a loosely coupled INS/GPS navigation system for a
large straddle carrier used in stevedoring. The discussion will
revolve around the actual implementation of the system on the
vehicle, the problems faced which would be typical in any GPS
implementation for land vehicle applications, and the results of
the vehicle traversing autonomously.
o
The
implementation of an attitude based GPS system loosely coupled
with INS for an Unmanned Air Vehicle application. This will
again discuss the relevant issues and the actual implementation.
Results of the vehicle traversing autonomously will also be
provided.
o
A
tightly coupled INS/GPS navigation system that will be
implemented on land, air and sea vehicles that traverses in
hostile environments where multipath and satellite outages are
expected.
o
The
implementation of an INS/GPS/Laser navigation system which will
inherently provide a higher integrity navigation system that
will also work in terrains where significant amounts of
multipath is expected.
Recent Advances in Real-Time Kinematic Technology
Author:
Dr Nicholas C. Talbot, Trimble Navigation,
Australia
Real-Time
Kinematic (RTK) technology has been commercially available since
1993. RTK delivers centimetre-level accuracy virtually
instantaneously, which makes the system suitable for a wide
range of applications. Early RTK systems had limited
functionality, for example a manual initialisation process was
needed before accurate results could be obtained. On-The-Fly (OTF)
initialisation simplifies RTK positioning; the GPS equipment
automatically handles initialisation irrespective of
user-motion. RTK equipment has been refined for various
applications such as machine guidance, surveying, agriculture
and precise navigation. However, some important limitations to
RTK positioning still remain. For example, the separation
between the user and a reference station is restricted to 10km.
A
report on the most recent advances in RTK technology is given.
In particular, enhancements that extend the operating range of
RTK are presented.
Receiver
Technology
Author:
Dr Nicholas C.
Talbot, Trimble Navigation, Australia
GPS
receiver technology has progressed significantly over the last
20 years. GPS wristwatches are now available and further
reductions in size and power consumption are expected to follow.
For high-end centimetre-level GPS receiver technology, the
evolution has been just as radical as hand-held user sets. Not
only has the physical size of equipment been reduced, but there
have also been quantum leaps in the underlying signal tracking
technology and equipment performance. An historical review of
high-end GPS equipment will be given for the past two decades.
GPSNet
A Victorian permanent GPS tracking network
Authors:
Nick
Talbot and Kefei Zhang, Department
of Geospatial Science, RMIT University, Australia
Martin
Hale and James Millner, Land Victoria, Natural Resources and
Environment, Australia.
Land
Victoria, within the Department of Natural Resources and
Environment, initiated an ambitious project in 1996 to establish
a GPS tracking network in Victoria. The system is termed GPSnet
and is designed to enhance the Victorian geodetic framework and
to provide easy access to accurate positioning information for a
wide user community across the state. The average spacing of
base stations is approximately 50km in the greater Melbourne
region and 100km in rural Victoria.
GPSnet is an integral part of
the new geodetic strategy for
Victoria and is being established in partnership with industry
and academia. GPSnet
currently consists of 9 operating base stations and will contain
20 stations upon completion.
The network records, distributes and archives GPS data
for accurate position determination with post processing
techniques. The
GPSnet system provides a mechanism for centimetre-positioning
relative to the National Spatial Reference Systems (Geocentric
Datum Australia 1994 and the Australian Geodetic Datum 1966/84).
In the future real time transmission of GPSnet data will
enable near instantaneous centimetre-level accuracy positioning
by a single GPS receiver in the field.
Research
is under way at the Department of Geospatial Science, RMIT
University, to investigate the use of GPSnet for high-precision
real-time positioning applications in Victoria. In particular,
ship docking and intelligent transportation systems will be
trialed. Real-time applications demand wireless delivery of data
from GPSnet. Existing communication media will be analysed in
terms of protocol, cost, coverage and portability of user
equipment.
Adaptive
Antenna Arrays For GPS interference Localisation.
Authors:
M Trinkle and D
Gray, CSSIP, University of Adelaide, Australia
In
this paper, we present trial results investigating the use of an
antenna array for interference direction of arrival (DOA) estimation
with a view to source localisation.
Adaptive
antenna arrays have commonly been used for interference
rejection in GPS.
A digital beamformer can however be easily extended to
also determine the direction of arrivals (DOA) of the
interferences. To estimate the interference DOA, the array needs
to be calibrated, this condition is not required for the simple,
null-steering power minimisation algorithms often applied in GPS adaptive
antenna arrays.
CSSIP
built a prototype digital beamformer for GPS signals and in
joint field trials with DSTO and US contractors at Woomera
investigated the potential of the beamformer system to also
localise interfering sources.
The beamformer was mounted in a van and data was
collected at various angles and locations of the antenna array.
The
key idea, is to use a mobile, ground based antenna array to
measure the interference DOA(s)
at several locations and then determine the source
location(s) by triangulation. The accuracy of the localisation
will depend on the fidelity of the DOA estimate, which in turn
is influenced by the phase and amplitude errors in the array.
This
paper presents the phase and amplitude errors observed in the
array and their effect on various DOA estimation algorithms
including CBF, MVDR and MUSIC. The accuracy of the DOA estimate
was found to be within 1-2 degrees of the line-of-sight DOA
measurement. Finally, an example of source localisation using a
moving platform is given.
A
Navigation/Positioning Service Based on Pseudolites Installed on
Stratospheric Airships
Authors:
Toshiaki Tsujii, Chris Rizos, Jinling Wang, Liwen Dai
and Craig Roberts
School of
Geomatic Engineering, University of New South Wales, Australia
Masatoshi Harigae, Flight Systems Research Center, National Aerospace Laboratory, Japan
Recently,
some countries have begun conducting feasibility studies and
R&D projects on High Altitude Platform Systems (HAPS). Japan
has been investigating the use of an airship system that will
function as a stratospheric platform (altitude of about 20km)
for applications such as environmental monitoring,
communications and broadcasting. Remote
sensing from such an airship would be very effective because it
floats above the same ground area, permitting continuous
monitoring of the surface. However,
the precise positioning of the airship is one of the most
important technical challenges for such a project. In
addition, if pseudolites were mounted on the airships, their
GPS-like signals would be stable augmentations that would
improve the accuracy, availability, and integrity of GPS-based
positioning systems because the airship network would cover all
of Japan. The
accuracy of the pseudolite positions would be a limiting factor
for such a service since the PL 'ephemeris error' is more
serious than GPS due to the lower height of the airship. In
this paper, a conceptual design of the airship-based
augmentation system is first introduced. Then
some schemes for estimating the pseudolite position are
described, and the results of a preliminary experiment are
presented.
A Low Cost
Integrated Navigation and Guidance System for Unmanned Aircraft
Author:
Rodney A.
Walker, CRC For Satellite Systems, Queensland University of
Technology, Australia
The
avionics group at the Queensland University of Technology have
been developing automated systems for use in unmanned aircraft.
One recent project at QUT is the XRV4- Hummingbird, a 20kg VTOL
multi-engine aircraft designed for agricultural and industrial
applications. The aircraft required a high performance
navigation system that would survive in the harsh environment
found in aircraft of this size. However, due to market
pressures, the cost allocation for the navigation system was
$7K.
This
paper shows how an integrated solution was found using a Dynamic
Measurement Unit (Inertial Measurements), low cost GPS receiver,
air speed indicator, barometric altimeter and an electronic
compass. This solution provides excellent performance in hover
mode and acceptable performance in higher dynamic flight modes.
An extended kalman filter was implemented in a small embedded
microprocessor which eventually gave an unacceptable update rate
of 2Hz. Currently work is progressing to improve the bandwidth
of the filter to 10Hz.
The
paper also discusses some of the mechanical and mathematical
filtering that was required to obtain acceptable results from
lower costs sensors mounted in this high vibration environment.
A small discussion is also made about the GPS attitude
experiments that were conducted as part of this experiment.
Precision
Relative Positioning in Space
Authors:
Rodney A.Walker,
CRC For Satellite Systems, Queensland University of Technology,
Australia
Bruce Hannah,
AirServices Australia
One
of the proposed uses for GPS in the space programs is for
precision relative positioning applications where mm level and
sub mm level relative positioning information is required.
Examples of where this type of accuracy would be required are in
the proposed automated docking systems to be used on the
International Space Station and also the development of VLBI
experiments such as the Automated Formation Flyer program.
One
of the major problems however in using GPS for these
applications is spacecraft based multipath which corrupts the
GPS signal and reduces the ability of a receiver to be able to
make mm level range measurements. Theoretically, of course, the
GPS system is capable of mm level range measurements, however
multipath limits this capability.
This
paper shows how the CRC for Satellite Systems spaceborne
multipath research program is attempting to completely mitigate
the effects of spacecraft multipath and to allow mm level range
measurements to be made. This technique requires the
availability of highly accurate attitude information for the
spacecraft and a detailed engineering model of the spacecraft.
The technique shows how with careful analysis of the GPS antenna
location and with the development of a 3D multipath model,
errors can be mitigated in real-time.
GPS and Mobile
Computing in Local Government
Author:
Tracey Willmott,
GPS Co-Ordinator, City Of Whittlesea, Australia
By
harnessing a variety of spatial technologies, the City of
Whittlesea in Melbourne’s north has developed a mobile
computing system to improve many formerly manual processes. The
system uses GPS to provide position into a mobile version of the
Council’s GIS map base. Coupled with a link to the property
and rates database, field officers are able to verify, update
and enter new information about a number of processes, including
fire prevention, weed mapping, septic tank mapping and derelict
vehicle logging. The use of digital cameras and video mapping
systems is now also enhancing this spatial methodology. The
implementation of GPS and mobile GIS is very innovative within
local government and has saved the City of Whittlesea tens of
thousands of dollars, many weeks of field inspections, and has
improved customer relations between the Council and the
residents.
Road Transport Applications Of GPS
Authors:
Rocco Zito, BEng(Hons), Transport Systems Centre and School of Civil Engineering, University of
South Australia.
Michael A.P. Taylor, BEng(Hons), M.Eng.Sc, PhD, Transport Systems Centre,
University of South Australia
The
use of the Global Positioning System (GPS) has become
established as a standard surveying technique.
However the use of GPS to establish control points and
locate static objects, is only tapping part of its potential.
GPS can deliver accurate time tagged data about the
location, speed, and reliability of GPS at update rates of once
per second. This
makes it possible to track moving objects and hence opens up
many applications in the transport sector.
As
the transport industry has grown to appreciate the full
potential of GPS, transport applications have proliferated.
This paper reviews the current state of practice in
applying GPS to road transport, concentrating on applications
that involve moving vehicles.
These dynamic applications of GPS in the road transport
sector fall into several categories; fleet monitoring, route
guidance / navigation, Intelligent Transport Systems and road
system performance. Each
of these applications will be considered and highlighting by
practical examples.
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