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Project Report |
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United
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Dec
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MTDC |
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Comparison of GPS Receivers Under a Forest
Canopy with Selective Availability Off
ROUGH
DRAFT
Dick Karsky, Project Leader; Ken Chamberlain, Land Surveyor; Santiago Mancebo, Graduate Student USFS Volunteer; Don Patterson, Land Surveyor; and Tony Jasumback, GPS Consultant
Table of Contents
SA
Off ---------------------------------------------------------------------- 1
Test
courses
Powell test Course
--------------------------------------------
1
Lubrecht test
Course------------------------------------------ 2
Powell test Course
--------------------------------------------
3
Test
procedure ---------------------------------------------------------- 4
Receivers
tested -------------------------------------------------------- 5
PLGR
------------------------------------------------------------- 6
Garmin GPS III+
----------------------------------------------- 6
Trimble Pro XR
------------------------------------------------- 7
Trimble Geo 3 --------------------------------------------------- 7
Magellan Map 410
---------------------------------------------
8
Results
--------------------------------------------------------------------- 8
Post
processing --------------------------------------------------------- 11
Effect of
SNR on Accuracy-------------------------------------------- 12
Effect of
PDOP on Accuracy------------------------------------------ 13
Effect of
Using external antennas on receivers ------------------14
PLGR
better in canopy -------------------------------------------------14
Real
time vs post processed ------------------------------------------14
Effect
of battery voltage ----------------------------------------------- 15
Discussion
---------------------------------------------------------------- 16
General
comments ----------------------------------------------------- 17
Summary
------------------------------------------------------------------18
Appendix
A - Receiver comparison chart ---------------------- 19
About the authors
------------------------------------------------------ 21
Comparison of
GPS Receivers Under a Forest
Canopy with Selective Availability Off
Tests – Summer 2000
SA-off
On
May 1st President Clinton announced that Selective Availability (SA)
would be turned off effective midnight May 1, 2000. This degradation feature Selective Availability (SA) is the
intentional degradation of the Global Positioning System (GPS) signals. This
will mean that civilian users of GPS will be able to pinpoint locations up to
ten times more accurately than before. With SA off position accuracy in the
autonomous mode increased from +/- 100 meters to less than +/- 10 meters (see
Figure 1). The decision to discontinue SA is the latest measure in an on-going
effort to make GPS more responsive to civil and commercial users
worldwide. Last year, Vice President
Gore announced plans to modernize GPS by adding two new civilian signals to
enhance the civil
and
commercial service.
Figure
1. The change in position error when
SA turned off
Test
courses
Powell, Idaho
GPS test course
This
GPS test site is located on the Powell RD on the Clearwater NF. It is located on Highway US 12 near the Idaho
Highway Maintenance area about 12 miles west of Lolo Pass and about 55 miles SW
of Missoula, MT. The test site is
located near the Lochsa River, and has mountains on the north and south sides
of the course, with a obstructed angle of 10 degrees on those two sides. The canopy consists of large (24”-42”
d.b.h.) old growth Cedar and Spruce trees in a flat valley bottom with only a
small amount of understory and would be considered a heavy canopy at most of
the stations. The course has 11 turning
points or stations, making a polygon measuring 12.019 acres in size that can be
divided to produce 2 areas (see Figure 2).
The
ground survey traverse and geodetic control survey of the Powell, ID GPS test
course was done by R-1 engineering and the Cadastral Survey group, Lolo N.F for
MTDC. The conventional survey was
accomplished with a Topcon total station.
The GPS control survey was accomplished with four Trimble 4000SSE/SSI geodetic
GPS receivers with L1/L2 compact dome geodetic antennas operating in the static
mode. Three data sets were observed
from HARN (High Accuracy Reference Network) stations “LOLO GPS” and
“W522”. Final results were calculated
from a least squares adjustment utilizing fixed integer baselines from the
geodetic observations. GEOID99 model
was used for geoid separation estimates.
The error estimates for the network observations are in the 2-centimeter
range. Coordinates are NAD83 (1992)
Montana HARN Latitude, Longitude.
Figure 2. Site Diagram for Powell GPS test course
Lubrecht Test Course
The Lubrecht Test Course is located at the Lubrecht
Experimental Forest about 30 miles NE of Missoula, MT. This course is a polygon with seven turning
points (stations) and is located on gentle terrain, under a mixed Lodgepole and
Ponderosa Pine canopy. The trees are
about 19 meters tall with a minimal understory and would probably be classified
as a light to medium canopy. Station
B-31 is located in the open, with a clear view of the sky down to an angle of
15 degrees (See Figure 3).
N
Figure 3. Site Diagram for Lubrecht GPS Test Course
Clackmas test course
The
Pacific Northwest Regional Surveyor established a test course at the request of
the Forest Service's GPS Steering Group in a typical dense West Coast
Douglas-fir stand. The course is on gentle terrain in a second growth
Douglas-fir and western hemlock overstory (trees approximately 24 to 40 inches
d.b.h.) with a vine maple and red alder understory. It consists of 13 stations,
all accurately located within 0.05 meters. The area enclosed by the traverse
can be varied from 2.19 to 7.20 acres, depending on the stations chosen (see
Figure 4).
The
Test Network geographic positions were established by GPS and conventional
geodetic survey. These thirteen points are used to define five areas, which
range from 2.19 to 7.20 acres. Geographic positions for the network points are
accurate to 5 cm. Each point is monumented with 5/8" rebar with plastic
caps and a nearby orange carsonite fence post, with "survey monument"
sticker attached. All points are intervisible and the lines between the survey
points are brushed and flagged.
Figure 4. Site Plan for Clackmas
GPS Test Course
Test
procedure
The receivers were turned on and
allowed to collect data for approximately 20 minutes to insure that a current
almanac was stored in the receiver before the tests were run. External antennas were used on all receivers
for most of the tests. Some tests were
run with the built-in internal antennas to obtain a comparison between the 2
types of antennas. Different numbers of
positions (1, 60, and 120) were averaged at the different stations to determine
what affect that had on the accuracy.
When possible the PDOP (Precision Dilution of Precision) and EPE
(Estimated Position Error) values were monitored to determine what type of
constellation was being accessed by the receivers. The position errors obtained at each station were then averaged
over the complete course to determine the average error of the individual
receiver.
Receivers
tested
The receivers tested on the Lubrecht
and Powell courses were:
1.
Rockwell PLGR-96, PPS,
S/N 165268, with sw:613-9868-015
Software.
2.
Trimble Pro XR, S/N 0220174140 with TSC1, and Asset Surveyor
Ver. 5.00 software.
3.
Trimble GeoExplorer 3, S/N 0330040826, with Ver. 1.02
Firmware.
4.
Magellan Map 410 Receiver Ver. 1.05 Firmware
5.
Garmin GPS III, S/N 92113388, 2.05 Firmware
PLGR +96
The PLGR+96 FED is a
five-channel, single-frequency Precise Positioning System (PPS) P(Y) Code
receiver with built-in antenna. It has been evaluated in other MTDC reports and
the accuracy of the receiver hasn’t changed significantly with S/A turned
off. The receiver contains a security
module that can eliminate the positional error intentionally introduced when
selective availability (SA) was enabled and it decodes the encrypted signal,
which prevents its unauthorized use, called anti-spoof (AS). The receiver is
not classified, but it is an accountable property item and should remain in
control of the authorized user. It can
store 999 waypoints and has 15 user definable reversible routes that can have
up to 25 legs each. It has an external
power and antenna option. It is DGPS
ready.
Garmin GPS III+
The
Garmin GPS III is a
Differential-ready 12 parallel channel receiver that continuously tracks and
uses up to twelve satellites to compute and update a position. It has acquisition Times of, approx. 15
seconds warm and approx. 45 seconds cold. It has a continuous update rate of 1 second. It can store 500
waypoints with symbols and 20 reversible routes, and a track log of 1900
points. It has a built-in detailed
basemap that covers lakes, rivers, interstates, national/state highways, secondary
roads in metro areas, cities, railroads, airports and a detailed exit database
for the Federal Highway system). More detailed maps are an option. It has 106
different map datums. It has a NMEA 0183 and RTCM 104 DGPS corrections interface. It has an optional external antenna.
Trimble Pro XR
The
Trimble Pro XR is a 12-channel, real-time differential GPS receiver with an
integrated antenna. The antenna receives the GPS signal and the real-time
differential corrections broadcast by a radio beacon maintained by the U.S.
Coast Guard or the U.S. Army Corps of Engineers. The operator can select if
DGPS is to be used and which real-time broadcast station to use. It is capable of outputting both the real-time
differentially corrected position as well as the raw data for each position.
Data were collected using the Trimble System Controller (TSC1) data logger with
Asset Surveyor Software Version 5.00 The data collection interval was set at 1
second, with the PDOP and SNR masks set at 6, and the elevation mask set at 15.
Pathfinder Office Software Version 2.70 was used to differentially post process
the raw-position data and display both the post processed and
real-time-corrected position data. Base-station data for post processing were
obtained from the Forest Service base station in Missoula for the Powell and
Lubrecht Site. (http://www.fs.fed.us/database/gps/missoula.htm).
That station, was a About 30 miles from the Lubrecht Site and about 55 miles
from the Powell test site, and records data at 5-second intervals.
Trimble Geo 3
The GeoExplorer 3 receiver is small in size, and its portability and powerful features make the GeoExplorer 3 an ideal tool for creating and maintaining utility, urban and natural resource asset databases. It has an integrated, high-performance 12-channel GPS receiver and antenna. The receiver firmware provides for easy GIS data collection, easy data maintenance of existing GIS databases, cable-free real-time differential GPS with Beacon-on-a-Belt receiver and it provides ARC/INFO, AutoCAD, Intergraph, MGE, ERDAS and GRASS support. GPS Pathfinder Office software is included for data processing and GIS export.
Magellan Map 410
The Magellan
Map 410 is a 12 parallel-channel receiver with a detachable signal-sensitive
antenna. It has a built-in worldwide background map and detailed basemap for
the Americas includes cities, lakes, rivers, railroads, coastlines, interstate,
national and state highways. It has a
built in altimeter. It can store 500 waypoints and 20 routes with 30 legs. It automatically averages your position when
the receiver is stationary. It has 9
graphic navigation screens, a re-settable trip odometer, and
"EZstart" initialization and built-in simulator for training and
education. It has Upload/Download
Capability, has NMEA output and is DGPS ready. It has external antenna
capability.
Results
Most error results shown in
the following charts may be expressed in 2DRMS values. The 2DRMS value approximates the 95%
probability of error for a position.
This means that 95% of the time or 19 out of 20 position readings will
have an error less that what is shown on the charts. The formula used in the calculation of 2DRMS is:
2DRMS=2x((Mean
Error)2 +(Standard Deviation of Error)2)0.5
Figure 5. Chart shows the position error in 2DRMS,
(95% of the time the error will be less than shown), for the different
receivers on the Powell GPS test course. (120 records averaged).
The chart in figure 5 shows
the position errors for the different receivers on the Powell test course. The Trimble Pro XR and Geo 3 receivers
collected files that could be post-processed and those files were
post-processed in figure 5. The error over
the course with the Pro XR was often less than 2 meters under the forest canopy.
Figure 6 shows position errors for the different receivers on the Lubrecht test
course and the Trimble Pro XR and Geo 3 were not corrected or post-processed is
this graph. The position errors for the
Trimble Pro XR and Geo 3 receivers are more similar to the other receivers
compared to figure 5 because of the uncorrected or non-post processed
data. Most position errors were less
than 7 meters for all receivers except for the Magellan receiver.
Figure 6. This graph
shows the position errors at the different stations for the Lubrecht GPS test
Course. In this graph the Pro XR and
Geo 3 were not post-processed. (60 record average).
Station
31 is in the open and not under a forest canopy. As can be seen in figure 6, all of the receivers have position
errors of less than 5 meters. If all
the position records are averaged for all the stations on the course, an
overall position error can be determined for each receiver over the complete
GPS test course. This is shown in
Figure 7.
Figure 7. This graph shows the position error for each
of the receivers on the Lubrecht GPS test Course. In this graph, all position error records for each receiver,
shown in figure 6, were averaged for each station. The position errors for each
receiver, on all stations, on the whole course were then averaged to obtain an
overall position error for each receiver.
Figure 8. This graph shows the position error for each of the receivers at an open point (no canopy), near the MTDC office. In this graph, the position error was obtained by calculating an average position error for each of the different record sizes (1, 60, and 120 records) in the open. The 2DRMS value was then calculated from those values for each of the receivers.
Post-processing
As previously mentioned, the only receivers that collected data that could be post processed were the Geo 3 and the Trimble Pro XR. Figure 9 and 10 show the results of post processing data from those receivers for the different number of records averaged.
Figure 9. This graph compares the 2DRMS position error for the Trimble Geo 3
receiver when a different number of records are averaged. The files were post-processed and also
displayed on this graph. It shows the
potential for large errors if only a few positions are averaged.
Figure 10. This graph compares the 2DRMS position error
for the Trimble Pro XR receiver when a different number of records are
averaged. RT indicated real-time
corrected positions. The files were post-processed and also displayed on this
graph. Why the large error occurred for
the 120 record average-uncorrected is unexplainable, but it shows how much of that
error was removed by post processing.
Effect of SNR on position accuracy
Figure 11 shows the effect
of different SNR (Signal to Noise Ratio) values to position accuracy. As SNR increases so does the accuracy. However, setting the minimum SNR value to a
larger value, will normally cause the efficiency of data collection to go
down. The higher SNR values usually
will require waiting at positions for a longer period of time before the
stronger signals will be available to the receiver. Mancebo and Chamberlain have a more detailed discussion of the
SNR vs data collection efficiency in another paper.
Figure 11. Graph showing the effect of
SNR on position accuracy under canopy and in the open for 1 and 50 position
records.
Effect of PDOP on Position accuracy
Figure 12: This graph shows the accuracy of various receiver configurations at the forested Clackamas Test Course for 50 seconds of data at various PDOP settings.
As can be seen from figure 12, the accuracy will decrease as
PDOP increases. This data was collected
on the Clackamas Test Course with the GeoExplorer 3 receiver. The effect of post-processing is also
displayed in this graph. Post-processed
data collected with a PDOP of 12 was more accurate than uncorrected data with a
PDOP of 4.
Effect of using external
antennas on the receivers
All but the Trimble Pro XR
have internal antennas. In the open,
under no tree canopies, the internal antennas are usually adequate. However under the forest canopy, external antennas
can give better accuracies. Figure 13
is an example of the improved results for the Garmin GPS III+. The results will differ for the different
receivers but the external antennas are more sensitive and are usually placed
on a range pole higher than the operator’s head thereby reducing signal
blockage.
Figure 13. This graph shows the effect of using an internal and external
antenna and the effect it has on 2DRMS position accuracy. These values obtained for the different stations
are calculated from the different number of position averaged.
PLGR better in canopy
The PLGR acquires positions better
in canopy than the C/A code receivers.
This is possibly due to the fact that the P(Y) code chipping rate (The
frequency at which the P code chip code is transmitted) is an order of
magnitude higher than the C/A code.
Under an open canopy the accuracy may not be as good as some of the C/A
code but is comparable under the canopy.
The major advantage to the receiver is that it is simple to use and the
data acquisition is much more efficient. However as shown in a later, figure
16, if a poor constellation is being used to calculate a position, a larger
position error is obtained.
Real time vs post processed
Real-time positions or DGPS
positions are positions that are corrected real time, with correction signals
sent to the receiver from a beacon DGPS station or via Satellite from a network
of ground stations. These signals are received and the data corrected
real-time. Post processing real-time
data doesn’t significantly increase the position accuracy most of the time but
usually does improve it. The
“down-side” to real time data collection is that sometimes the correction
signal is interrupted or is “attenuated”.
If the files are collected and brought back to the office, it is usually
quicker and more efficient to post process the data later at the office. Figures 14 and 15 show the position error
results of Real-Time (DGPS) and post processing data.
Figure 14. This graph shows the effect of post-processing un-corrected data (ssf) files and post processing real-time corrected data (all data was processed).
Figure 15. This illustration shows that post processing increases accuracy
of the position. This increase is
significant for uncorrected data but is very small when post processing
real-time data.
Effect of battery voltage
Battery voltage has an
effect on PLGR’s and Trimble GeoExplorer II’s.
The symptoms of Trimble Geoexplorer II’s and PLGRs with weak batteries
are that the receivers will have difficulty acquire a signal or GPS position
under canopy. When batteries are
replaced, the signal is more easily acquired.
The Garmin GPS III+ and Magellan Map 410 were operated until battery low
indication on the display panel was received. A position, in open canopy, with
low voltage was recorded and then the batteries were replaced, and same
positions retaken. The results showed
little effect on position error with low and new batteries for those 2
receivers.
Discussion
In some of our tests, the
smaller units such as the Garmin GPS III were used as an indicator of satellite
constellation. The trend seemed to be that if 6-7 Satellites with good PDOP
were displayed on the “skyview” screen, the position accuracy was usually
good. The Garmin GPS III+ receivers
usually produced good accuracy results.
They typically are on par with the Trimble Geo 3's. However if a bad constellation is present,
the Garmin will still record data. The
Garmin doesn't have a PDOP or SNR mask, and it doesn't have a minimum mask
angle (which would reduce the potential for multipath signals to be received by
the GPS receiver). If they can see a
satellite they will use it in a solution.
What was found is that if the receiver is tracking 5-7 satellites with
good SNR values on the skyview screen you will probably get accurate
results. If you have only 4 or 5 weak
satellites the results won't be that good.
So with receivers without PDOP and SNR mask, if that is not observed,
you may be getting some poor data.
The masks on the Trimble Geo 3 were set to PDOP=16, SNR=2, and
Elevation=3 degrees. It was then run on the test course with the PLGR, and
Garmin on the Powell course when the satellite constellation was poor (Mission
Plan indicated a PDOP > 16 during that time period). We got similar position errors from the
PLGR, Garmin, and Geo 3 (Errors greater that 20 meters) and of course the Pro
XR was not recording because the masks were set so it would only receive good
data These results are shown in figure 16.
The Garmin will also record 2-D
fixes using only 3 satellites when averaging waypoints and this was being done
while these tests were run. We used the Garmin with their external antenna,
which did improve accuracy as is illustrated in Figure 13.
Figure 16. This chart shows position error for three receivers when the satellite constellation was poor. The mission planning software indicated that the maximum PDOP (Position Dilution of Precision) at the time was about 16. The Geo 3 mask settings were changed to allow data to be recorded.
The conclusion is that if the constellation is bad (poor PDOP),
position errors will increase and the receivers will record positions even
though the EPE (Estimated Position Error) readout has reasonable values. Better receivers have PDOP, SNR, and
Elevation Angle masks that will reduce the probability of recording inaccurate
data. But with the better accuracy comes the “trade-off” of less efficiency.
There will be times when the receiver will have to wait as positions won’t be
recorded even though it may be tracking 5 or 6 satellites due to poor PDOP.
General comments
Some general comments about
the different receivers are:
- The Garmin GPSIII+ is a very user-friendly
receiver. It acquired satellite signals quickly, and averaging a waypoint
was easy to accomplish. The
factory DGPS antenna was not as sensitive as the Trimble and was not able
to receive a weak beacon signal when the Trimble Pro XR could acquire
one. There is no way to limit the
Maximum PDOP setting, the minimum SNR setting or the minimum elevation
angle.
- The Magellan Map 410 is also a user-friendly
receiver. However averaging a
waypoint is tricky because averaging starts as soon as the receiver quits
moving. One is never sure if some
positions from a few feet away are included in the average. Again the
factory DGPS antenna is not as sensitive as the Pro XR.
- The Trimble Pro XR is very easy to use and it
will inform you if a beacon station is available for Real-Time DGPS. It
gives information about that beacon signal, i.e. signal strength,
frequency, bit rate, and more.
Under a difficult canopy, it seems to take time to acquire a
satellite signal and a position.
This is due to the receiver mask settings, of PDOP, SNR, and
Elevation angle. It appears that
the other receivers are more sensitive and are more efficient but in
reality, the data received is not very good data and when comparing
position accuracy, the Pro XR gives better results.
- The Trimble Geo 3, with the internal antenna,
does not obtain positions as accurate as the Pro XR and sometimes the
other receivers. Using an
external antenna will provide a big accuracy improvement for this receiver.
- The PLGR is an “older technology” receiver,
which in the open, may not be as accurate as the newer receivers. It will acquire a signal under a dense
canopy easier that most of the C/A code receivers. It is easy to use but requires
“Keying” (Keying is inserting a code in the receiver to eliminate
selective availability (SA) and must be done annually). Previous to these
tests two PLGR receivers were compared on the Lubrecht test course, one
keyed with the P(Y) code and the other with the P(Y) code “zeroized” (zeroized
means the P(Y) code was removed and the receiver could only receive the
C/A civilian code) and the results compared. The P(Y) code version provided smaller position errors.
Summary
In
summary a good constellation is needed to get good data. If data is recorded, it will record
positions with more error. The small handheld inexpensive receivers will
provide accurate positions in the open and under a medium canopy when good PDOP
is available, but that may not be the case under heavy canopy or when the satellite
constellation is poor (poor PDOP).
Post
processing data still increases position accuracy, typically 2 – 4 meters. If data isn’t needed immediately it is
easier and more efficient to collect data (ssf files) and post process the
information rather than trying to collect real-time DGPS positions. This may change in the future when more
real-time DGPS stations come on line and all areas have double coverage (when a
location can receive a real-time DGPS signal from 2 different beacon stations).
A
report written by Santiago Mancebo and Ken Chamberlain discuss the results of
the effects of SNR and PDOP on position accuracy for these receivers and what
effect they have on data acquisition efficiency. This study was done on the
Clackmas Test Course, which has a heavy forest canopy and is similar to the
Powell GPS Test course.
Further
work that should be done is:
·
What is the correlation
if any, between the EPE value indicated on the GPS receiver and the real error?
·
More testing of the
DGPS real-time accuracy of the different receivers and the efficiency of
collecting DGPS data.
·
More tests of how much
post processing improves the accuracy of DGPS real-time positions.
·
The newer PLGR II, dual
frequency receiver should be evaluated.
Appendix A: Summary Table of Different GPS Receivers
|
Receiver |
Advantages |
Disadvantages |
Accuracy(Typical) |
Approx. Cost |
|
Trimble Pro XR |
· Can log Data · Can Post Process · Can export data to Arc/Info · Real-Time DGPS · Accuracy |
· Cost · Bulky |
Open Canopy 1-4 m Under Canopy 2 – 5 m |
$10,000 |
|
Trimble Geo 3 |
· Can log Data · Can Post Process · Can export data to Arc/Info · Real-Time DGPS |
· Cost · Not as accurate as Pro XR · Should use External antenna |
Open Canopy 1-4 m Under Canopy (120 positions) Lubrecht 2.4 – 7.7 m Post-Processed 2.5 – 7.8 m |
$4,500 |
|
Rockwell PLGR |
· Acquires GPS Signal in difficult canopy and terrain better than C/A signal · Simple to Use |
· Must record positions manually. Doesn’t log data without external data logging device. · Can’t Post Process · Can do Real-Time processing but then uses the C/A signal. · Accuracy not as good as post processed other receivers. · A military accountable item. · Must be re-keyed annually. |
Open Canopy 1-4 m Under Canopy (120 positions) Lubrecht 2.5 – 6 m |
$3,500 Ext. Ant. +$300 |
|
Trimble Centurion |
· Acquires GPS Signal in difficult canopy and terrain better than C/A signal · Simple to Use |
· Can use Asset surveyor software and TDC1 data logger to collect data. · Can’t Post-Process “P” code data. · Can do Real-Time processing but then uses the C/A signal. · Accuracy not as good as post processed other receivers. · A military accountable item. · Must be re-keyed annually. |
Open Canopy 1-4 m Under Canopy (120 positions) Lubrecht 2.5 – 6 m |
$4,900 Ext. Ant. +$300 |
|
Garmin III+ |
· Cost · Ease of Use · Readily available · Records Waypoints and can download to their software · Can do Real-Time DGPS with extra optional receiver with some work · Can Average Waypoints |
· Can’t export data into ARC/Info · Can’t Post Process · Should use External antenna |
Open Canopy 1-3 m Under Canopy (Ave 120 positions) 2.5 – 5 m |
$350-Unit Soft. & Ext. Ant +$200 DGPS +$300 |
|
Magellan 400 |
· Cost · Ease of Use · Readily available · Records Waypoints and can download to their software · Can do Real-Time DGPS with extra optional receiver with some work · Can average waypoints |
· Can’t export data into ARC/Info · Can’t Post Process · Should use External antenna · Waypoint Averaging is tricky – starts when receiver quits moving |
Open Canopy 2-7 m Under Canopy Lubrecht (60 position average) 3 – 12.2 m |
$350 - Unit Software $60+ Ant $100 |
Table 1. Comparison of various
Receivers Preliminary only
About
the Authors
Dick Karsky has
a bachelor’s degree in agricultural engineering from North Dakota State
University and a Masters degree in agricultural engineering from the University
of Minnesota. He worked as a project leader in most resource areas in the USDA
Forest service since coming to the Missoula Technology and Development Center
in 1977 and had been involved in the GPS program since 1996. His current
position is Program Leader in Forest Health and in Water, Soil and Air.
Tony Jasumback, is a retired MTDC -USFS employee and was the GPS
Project Leader at MTDC, and was involved in the development and evaluation of
GPS equipment for Forest Service use since 1984.
Ken Chamberlain, is a cadastral surveyor for the USFS at the
Regional Office in Region6 at Portland OR.
Santiago Mancebo, is a Graduate student from Spain and USFS
Volunteer employee
Don Patterson is a land surveyor in the Northern Region
Engineering Office in Missoula, MT. He is a licensed land surveyor in Wyoming
and Montana. He holds a bachelor’s degree in surveying from the Oregon
Institute of Technology. Don worked for the BLM in Alaska and Wyoming before
coming to the Northern Region.
Single hard copies of this
document may be ordered from:
USDA Forest Service
Missoula Technology & Development Center
Building 1, Fort Missoula
Missoula, MT 59804-7294
Phone: (406) 329-3978
Fax: (406) 329-3719
E-mail: pubs_wo_mtdc@fs.fed.us
For further technical
information, contact Dick Karsky at the address above.
Phone: (406) 329-3921
Fax: (406) 329-3719
E-mail: rkarsky@fs.fed.us
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