January/February
2001
New
Applications Make NDGPS More Pervasive
by
James A. Arnold
Imagine
that you are driving through Minnesota on a January evening. You know
that blizzard conditions have been forecast for the area. Snow is
falling, and driver advisories have been posted for the entire region.
Are you very nervous? No! Not when Minnesota has equipped their snowplows
with Nationwide Differential Global Positioning System (NDGPS) receivers.
With NDGPS, the roads can be kept clear even in the worst conditions.
You also know your vehicle is equipped with NDGPS linked to your cell
phone to automatically alert emergency service personnel if you are
involved in an accident. And you know that each NDGPS reference location
also contains precipitable water vapor sensors that have increased
the accuracy of the precipitation forecasts from the National Weather
Service.
And that's not all of the many advantages of NDGPS. With an accurate
forecast from the National Weather Service telling travelers where
a blizzard is headed and when it will arrive with NDGPS, travelers
may be able to navigate around the blizzard.
Does this imaginary scenario sound too good to be true? It shouldn't
because all of these applications of NDGPS are being developed by
government scientists, who can envision these and other uses for this
new service. It has been called an "enabling technology"
because it will allow other technologies to function at improved levels.
In a previous article ("A More Precise Sense of Where We
Are,"
Public Roads, Volume 63, Number 4, January/February 2000, pages
7-13), co-authors David Smallen, Rudy Persaud, and I described the
emerging NDGPS. In summary, this nationwide system of 91-meter- (300-foot-)
high reference towers is being created to improve the accuracy of
the positioning information obtained via radio signals emitted by
the 24 Global Positioning System (GPS) satellites traveling in orbit
around the Earth.
Dramatic
Improvements in Accuracy
While the civilian GPS signal, known as the Standard Positioning Service
(SPS), currently provides positioning information for civilian hikers,
boaters, users of in-vehicle positioning devices, and others, the
accuracy of SPS is limited for various reasons to approximately 25
meters (82 feet). Preliminary work has shown that even a limited NDGPS
can improve that accuracy to approximately 1 meter (3 feet). Accuracy
is expected to improve to 2 to 20 centimeters (0.8 to eight inches)
over the next few years as new correction techniques evolve.
Improvements are possible because the fixed location of an NDGPS tower
is compared with the GPS-determined location of the tower and the
measured difference between actual location and GPS location can be
used as a correction factor. This factor or "signal" is
transmitted to mobile receivers in vehicles or in the hands of individuals.
These receivers use the corrective signal to adjust the GPS location
so that it becomes the more accurate NDGPS location. The closer the
receiver is to the transmitter, the more accurate is the correction
and, thus, the adjusted location. Also, with more towers, it is possible
to perform a dual-tower fixed-location comparison for even more precise
accuracy.
The NDGPS installation plan calls for the deployment of 80 low-frequency
broadcast stations by the end of 2002. Significant factors have been
incorporated into the plan to increase its cost-effectiveness by reusing
existing resources. The new NDGPS broadcast stations will be redesigned,
decommissioned Ground Wave Emergency Network (GWEN) towers provided
to the Department of Transportation (DOT) by the U.S. Air Force. In
addition, NDGPS will be sharing the use of the U.S. Coast Guard's
Maritime Differential GPS sites and the U.S. Army Corps of Engineer
sites. NDGPS is expected to have 125 to 135 involved sites by 2004.
This massive undertaking is possible because of efficient and economical
cooperation among the U.S. departments of Transportation, Defense,
and Commerce. DOT has the primary coordinating responsibility, and
within DOT, the Federal Railroad Administration is leading the development
of the emerging NDGPS service. Even though NDGPS at present has not
reached its full potential, many applications of this service are
evolving.
Improvements
in Weather Forecasting
For
example, one agency within the Department of Commerce has already
discovered a very important use for more accurate positioning. Scientists
in Boulder, Colo., at the Forecast Systems Laboratory (FSL) of the
National Oceanic and Atmospheric Administration (NOAA) have been investigating
the use of NDGPS to improve weather forecasting and climate monitoring.
Seth Gutman of the FSL reports that NDGPS data does have a positive
effect on weather forecasting vectors.
For some time, FSL has been using GPS data to measure the delays in
the transfer of signals from the GPS satellites caused by water vapor
in the atmosphere. Although the total amount of water vapor could
be measured through calculations, it was not clear that this information
helped in weather forecasting. Work with the new NDGPS has provided
the ability to measure the slowing of satellite signals by water vapor
with unprecedented accuracy.
The improved accuracy has resulted in another application for NDGPS
and a new weather observation system at NOAA. According to Gutman,
scientists and engineers at FSL are now building the prototype of
an operational NDGPS-integrated perceptible water vapor (IPWV) observation
system for the National Weather Service. This modified NDGPS system
is being built in collaboration with FHWA, the Coast Guard, and the
National Geodetic Survey/Continuously Operating Reference Station
(NGS/CORS).
The system uses ground-based GPS meteorological observation instruments
installed at the NDGPS tower sites. This is a relatively inexpensive
system because each site basically consists of a barometer and a thermometer
and devices to collect and transmit the GPS and meteorological data
in near real time. The NDGPS stations will be providing water vapor-caused,
satellite signal-delay data. The connected NGS ground instruments
will collect the data and use it to calculate accurate water vapor
information. This information will be sent to NOAA via CORS every
30 minutes.
A dozen NDGPS sites are currently in the process of being retrofitted
to include the weather observation tools, and FHWA has transferred
funds to FSL to support creation of an additional 22 GPS Surface Observation
Systems (GSOS).
It already has been shown that including NDGPS data in modern weather-prediction
models improves the accuracy of weather forecasts, especially under
active weather conditions when it is needed most. NOAA scientists
are confident that data collected through the NDGPS stations will
be used in the next-generation National Weather Forecasting Model.
NOAA views its collaboration with FHWA and other government agencies
as a very unusual and beneficial opportunity to use NDGPS data for
a low-cost improvement in weather forecasting.
New
Applications Emerging Fast
Dave Gorg of the Minnesota DOT reports that a host of new applications
of the improved positioning accuracy available through NDGPS are being
planned. It is expected that immediate positioning will be routinely
accurate to within 5 to 10 centimeters, which is the degree of accuracy
that many transportation vehicles and transportation support services
need to operate safely and successfully.
Snowplows, in particular, have a very small margin for error when
they are operating near guardrails, light standards, and other safety
devices or near bridges, overpasses, and public areas. Also, when
snowplows are clearing airport runways, it is of the utmost importance
that the entire runway is cleared quickly without running into any
adjacent safety or signal equipment.
In Minnesota, a computer-driven heads-up display that presents accurate
positioning information from NDGPS has been developed. This device
flips down much like a sun visor so that it can be used when needed
and placed out of the way when visibility is not bad enough to warrant
its use. With this display, the snowplow operator can move ahead with
confidence even in poor visibility conditions. (For more information
about "smart" snowplows, see "Safe Plowing - Applying
Intelligent Vehicle Technology" on page 3.)
Mapping roads will be a high-priority function for NDGPS. The description
and location of all roads will be more precise with more accurate
information about topography and the positions of road safety appurtenances
and signage. With better information available from the NDGPS map
- better quantitatively and qualitatively - many more applications
will be possible.
For example, the highway patrol and other law enforcement agencies
will be able to examine and describe vehicle accidents more precisely;
highly accurate measures of accident scenes will be possible. Aerial
photographs (digital orthophotos), which employ "white targets"
on the ground, can be compared with NDGPS exact positioning data to
document the history of accidents in selected areas. Such comparisons
should reveal clues about accident trends, such as safety hazards
and/or possible road design flaws that may contribute to accidents.
Both highway safety officials and insurance company representatives
would be interested in obtaining and using such information to track
and prevent accidents.
An application similar to the snowplow heads-up display is being planned
for buses in the Minneapolis-St. Paul area, Dave Gorg reports. Major
highways through the cities are built with a 10-foot (3.05-meter)
emergency lane. The buses are 9 feet (2.75 meters) wide. The plan
is to allow the buses to use the emergency lane as a bus-only express
lane during rush hours. But with the small margin for error - one
foot (0.3 meters) - the driver will need the assistance of an NDGPS
positioning map on the heads-up display.
Other NDGPS applications being planned today in Minnesota are well
worth mentioning and may stimulate more ideas in other states tomorrow.
For instance, utility companies are interested in mapping their underground
transmission lines more accurately. With NDGPS, it should be possible
to map these within one-foot accuracy. Is this important? Ask someone
who has seen a natural gas line explode when the line was ruptured
by drilling or digging because, as a result of inaccurate mapping,
no one knew the line was there. Also, utilities and state DOTs need
accurate right-of-way maps to facilitate the installation of fiber-optic
and similar communication transmission lines.
The
Many Possibilities of Precise Vehicle Positioning
Perhaps one of the most far-reaching applications involves knowing the
exact location of vehicles. With NDGPS, it will be possible to avoid
airplane collisions on the ground because a constantly updated map of
all objects, including vehicles and safety equipment as well as airplanes,
will be available.
Historical records of where vehicles were located at particular times
will also be possible. This may mean that trucking companies can explicitly
document their operations within a state - how many trucks, for how
long, at which weights, and on which highways. This could affect road-use
taxes.
In addition, other service vehicles, such as paving machines, bulldozers,
fire engines, and ambulances, could use the heads-up display to guide
and speed their efforts.
NDGPS could be a boon to farmers also. Farmers may have many applications
for NDGPS as a tool for mapping their crop plantings, fertilizing, irrigating,
harvesting, and field use, as well as being a guide for their tractors
and other farm machinery.
|
This
snowplow, which is jointly operated by the Intelligent Vehicles
Laboratory of the University of Minnesota's ITS Institute and
the Minnesota Department of Transportation, is presently being
used in experiments to determine the design details of driver
assistive technology used for operating vehicles under low-visibility
conditions. The design includes high-accuracy DGPS, digital maps,
radar, and an innovative heads-up display. |
The
list of potential NDGPS applications is only beginning to be compiled,
and already it seems boundless.
The best news is that the NDGPS modernization program is proceeding
rapidly. As the new data messages are developed, the accuracy of positioning
information improves. True "ground zero" measures can be reached
with 20-centimeter (8-inch) accuracy, down from the current three meters
(10 feet). The implications of this change are as dramatic as the 1-to-15
ratio in improved accuracy.
The new system will be tested in Maryland later this spring. Funds have
been made available to begin research/testing soon in Hagerstown, Md.,
with the emphasis of the work to be on "service applications,"
including some of the possibilities previously mentioned.
In short, NDGPS technology will soon be available for everyone to use
and benefit from in a host of ways never before possible. The number
of ways that NDGPS will be employed is as great as the imaginations
of those who consider new applications.
James
A. Arnold is a research electronics engineer with the Federal
Highway Administration's Office of Operations Research and Development.
He received his bachelor's degree in electrical engineering from the
University of Delaware in 1985 and his master's degree in electrical
engineering from the Florida Institute of Technology in 1990. His
experience includes the development of military communication systems
and commercial communication systems related to intelligent transportation
systems; technical evaluation of an integrated GPS for the U.S. Navy;
technical management of the 1994 Augmented GPS study completed for
the Department of Transportation; network design, spectrum planning,
and environmental analysis for NDGPS; and service as the chairman
of the State and Local Municipality Subcommittee of the Civil GPS
Service Interface Committee (CGSIC). His primary responsibilities
at FHWA include radionavigation and wireless communications in support
of intelligent transportation systems.
Other
Articles in this Issue:
Learning
to Beat Snow and Ice
Safe
Plowing - Applying Intelligent Vehicle Technology
Improving
Roadside Safety by Computer Simulation
Using
the Computer and DYNA3D to save lives
LS-DYNA:
A Computer Modeling Success Story
Preservation
of Wetlands on the Federal-Aid Highway System
Internal
FHWA Partnership Leverages Technology and Innovation
New
Applications Make NDGPS More Pervasive
Center
for Excellence in Advanced Traffic and Logistics Algorithms and Systems
(ATLAS)
National
Work Zone Awareness Week (April 9 to 12) - Enhancing Safety and Mobility
in Work Zones