wisconsin dot experiences with low altitude flights using aircraft with gps mr-rst technology...
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Wisconsin DOT Experiences Wisconsin DOT Experiences with Low Altitude Flights usingwith Low Altitude Flights using
Aircraft with GPS Aircraft with GPS
MR-RST Technology Exchange Meeting
Pyle Center, University of Wisconsin
14-15 April 2003
Wisconsin Department of Transportation
Geodetic Surveys Unit
15 April 2003 Low Altitude ABGPS 2
IssueIssue
Determine if Airborne Global Positioning System Determine if Airborne Global Positioning System (ABGPS) can Produce Accuracies as Comparable to (ABGPS) can Produce Accuracies as Comparable to
Conventional Equipment and Procedures for Low Conventional Equipment and Procedures for Low Altitude Flights.Altitude Flights.
15 April 2003 Low Altitude ABGPS 3
Test Approach CriteriaTest Approach Criteria
Utilize ABGPS on a 1:3600 large scale block mapping Utilize ABGPS on a 1:3600 large scale block mapping project around Campbellsport, WI.project around Campbellsport, WI.
Targets were placed at defined locations and surveyed to Targets were placed at defined locations and surveyed to established horizontal and vertical positions.established horizontal and vertical positions.
Trimble 4000 SSi’s were used to collect data in the aircraft Trimble 4000 SSi’s were used to collect data in the aircraft and simultaneously on the ground at three locations and simultaneously on the ground at three locations (Juneau, Dundee, and Campbellsport, WI).(Juneau, Dundee, and Campbellsport, WI).
One (1) second data collection rate was used.One (1) second data collection rate was used. Data was processed by WisDOT using Trimble Geomatics Data was processed by WisDOT using Trimble Geomatics
Office (TGO) software and by Woolpert using TGO and Office (TGO) software and by Woolpert using TGO and GrafNav softwares.GrafNav softwares.
Compare camera photo centers differences between Compare camera photo centers differences between ABGPS and Analytical Triangulation (AT) solutions. ABGPS and Analytical Triangulation (AT) solutions.
15 April 2003 Low Altitude ABGPS 4
Project LocationProject Location
Base Station Locations
Juneau GPS (40 km SW of site)
Dundee GPS (10 km NE of site)
T124 (on site)
Event Markers are Blue “Diamonds”
N
15 April 2003 Low Altitude ABGPS 5
Comparison ViewpointComparison Viewpoint
WisDOT processed data from Juneau GPS, Dundee GPS, WisDOT processed data from Juneau GPS, Dundee GPS, and T124 mobile base stations using TGO.and T124 mobile base stations using TGO.
Woolpert processed data from same mobile base stations Woolpert processed data from same mobile base stations using TGO and GrafNav.using TGO and GrafNav.
Comparisons were made to AT solutions and differences Comparisons were made to AT solutions and differences between WisDOT and Woolpert indicate similar results.between WisDOT and Woolpert indicate similar results.
15 April 2003 Low Altitude ABGPS 6
ResultsResults
Mobile Base Station CommentComputed Rank w/
X, Y, & O-Ht
Computed Rank w/ X, Y, &
O-Ht & offset
X DIF Mean
value (m)
Y DIF Mean
value (m)
O-HT DIF Mean
value (m)
O-HT w/ offset
T124 On Site 4.0 3.7 -0.111 0.292 -1.277 0.064DUNDEE GPS 9.2 km NE 4.7 3.0 -0.127 0.280 -1.286 0.055JUNEAU GPS 39.8 km SW 5.3 5.3 -0.217 -0.079 -4.115 -2.774
T124 & DUNDEE GPS On Site & Closest 4.7 3.7 -0.119 0.286 -1.281 0.060T124 & JUNEAU GPS On Site & Farthest 2.3 4.0 0.130 0.052 -0.357 0.984DUNDEE GPS & JUNEAU GPS
Off Site3.3 4.3
-0.201 -0.079 -0.748 0.593
T124, DUNDEE GPS &JUNEAU GPS
All Base Stations
3.3 3.7
-0.114 0.285 -1.269 0.072
15 April 2003 Low Altitude ABGPS 7
Analysis of Data SetsAnalysis of Data Sets
PDOP plots found to contain spikes indicating some PDOP plots found to contain spikes indicating some interference.interference.
Number of satellites was sufficient before, during, and after Number of satellites was sufficient before, during, and after the flight.the flight.
Continuous tracking of satellites between aircraft and base Continuous tracking of satellites between aircraft and base stations indicated cycle slips.stations indicated cycle slips.
Cycle slips occurred systematically during turns before Cycle slips occurred systematically during turns before and after flight lines.and after flight lines.
Loss of lock occurred at a rate that was too frequent thus the processor was unable to properly fix the correct set of integers resulting in poor GPS derived coordinates.
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Flight TrajectoryFlight Trajectory
15 April 2003 Low Altitude ABGPS 9
DOP PlotsDOP Plots
15 April 2003 Low Altitude ABGPS 10
Considerations for ImprovementConsiderations for Improvement
The pilots need to hold the plane as flat as possible and to The pilots need to hold the plane as flat as possible and to graduate into a flatter turn before and after each flight line.graduate into a flatter turn before and after each flight line.
Investigate using a different GPS antenna instead of the Investigate using a different GPS antenna instead of the Tecom antenna.Tecom antenna.
Investigate using a different kinematic processor that is Investigate using a different kinematic processor that is more robust thus allowing the user to manipulate the data more robust thus allowing the user to manipulate the data with greater options.with greater options.
Use base stations less than 25 km to ensure higher Use base stations less than 25 km to ensure higher probability of quality coordinate determination. probability of quality coordinate determination.
15 April 2003 Low Altitude ABGPS 11
Future ConsiderationsFuture Considerations
Perform more trials as time allows.Perform more trials as time allows. Investigate cost benefit analysis of low altitude flights Investigate cost benefit analysis of low altitude flights
versus present day base control and positioning tools.versus present day base control and positioning tools. Success might be limited to small scale photogrammetric Success might be limited to small scale photogrammetric
projects in block configuration.projects in block configuration.
15 April 2003 Low Altitude ABGPS 12
Questions/Comments?Questions/Comments?