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University of Colorado
GPS as a remote sensing tool
Stephan Esterhuizen
Colorado Center for Astrodynamic Research
University of Colorado2006
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University of Colorado
Background
� Used bistatic radar concept� Two antennas
1) Direct antenna2) Reflected antenna
� Direct signal tracked with conventional methods
� Reflected signalobserved by using information fromdirect signal tracking
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University of Colorado
NOAA BAO � 300m Tower
Direct and Reflected RCP/LCPantennas
� 45 degree 3dB beamwidth� 15dBi gain
Carriage at bottom of tower for installation of equipment
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University of Colorado
Asheville, NC flight
� Platform: NASA G5� Flew figure 8 pattern over rough terrain� Direct and reflected antennas had a
hemispherical gain pattern
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University of Colorado
Ames, Iowa Terrain
� Flew in Bonanza plane operated by Iowa University's Operator Performance Lab (OPL)
� Terrain mostly farmland and some bodies of water
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University of Colorado
Water/Land Boundary
Lower Left is 3955232 Northing, 339200 Easting, Zone 17 (UTM), 32m Res., ind=2801
Delta East (km)
Del
ta N
orth
(km
)
0 5 10 150
2
4
6
8
10
12
14
16
18
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University of Colorado
Method continued...
−1 0 1 2 3 4 50.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8x 10
5 100ms correlation waveform
Chips
Acc
umul
atio
n va
lue
Peak
Noise
� 2s accumulations: SNR computed by taking 20*log10(PeakCorr/NoiseCorr)
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University of Colorado
Reflected SNR - Water
� Reflected SNR over water for two satellites
−4 −2 0 2 4 6−2
0
2
4
6
8
10
12
14
16
18
Chips
SN
R (
dB)
2 second averaged reflected SNR over water for PRN26 and PRN29
PRN26 Time1PRN26 Time2PRN29 Time1PRN29 Time2
PRN26-T1 PRN26-T2 PRN29-T1 PRN29-T2SNR 15.5dB 15.5dB 15.99dB 16.18dBStd 1.01dB 0.96dB 0.68dB 0.71dBWidth 1.6 chips 1.6 chips 1.6 chips 1.6 chips
Lower Left is 4616004 Northing, 442400 Easting, Zone 15 (UTM), 4m Res., ind=3050/9000
Delta East (km)
Del
ta N
orth
(km
)
0 0.5 1 1.5 20
0.5
1
1.5
2
1
1
2
2
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University of Colorado
Reflected SNR - Forest
� Reflected SNR over forest for PRN14T1 T2 T3 T4
SNR 2.3dB 1.97dB 1.88dB 1.18dBStd 0.06dB 0.05dB 0.11dB 0.03dBWidth 1.9 chips 2.7 chips 2.6 chips 3.2 chips
−6 −4 −2 0 2 4 6 8 10−0.5
0
0.5
1
1.5
2
2.5
Chips
SN
R (
dB)
2 second averaged reflected SNR over forest for PRN14
PRN14 Time1PRN14 Time2PRN14 Time3PRN14 Time4
Lower Left is 3966404 Northing, 356000 Easting, Zone 17 (UTM), 4m Res., ind=2700/12000
Delta East (km)
Del
ta N
orth
(km
)
0 0.5 1 1.5 20
0.5
1
1.5
2
12
34
� Reflected SNR over forest for PRN14
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University of Colorado
New receiver design
� Designing new receiver because old equipment too large to fly on smaller platforms:� UAVs� Balloons
� Have not flown receivers in space yet, but balloon would be the next best thing
AnalogFrontend
Data Bridge
DirectAntenna
ReflectedAntenna
AD
C
Host
Single BoardComputer
Storage
USB
PowerAnalog Box
Processing Box
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University of Colorado
Payload distribution
Processing box
Mass: 2.7kg (5.9lbs)Size : 13cm x 13cm x 10cm (5.1� x 5.1� x 3.9�)Components: Computer, Hard disk, Battery
Analog box
Mass: 1.0kg (2.2lbs)Size : 7cm x 12cm x 5cm (2.6� x 4.7� x 2�)Components: Antennas, Analog frontend, Databridge
DirectAntenna
ReflectedAntenna
USB +PWR
Total Mass ~= 3.7kg (8.1 lbs)
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University of Colorado
Special Considerations
� Disk� Dumping data to disk at 16MB/s � can't use
solid state store (too expensive)� Will use mechanical hard disk� Need to mount HD intelligently to prevent disk
failure due to high accelerations/jerks.� Temperature
� Both boxes need to be kept between 0C and 60C
� Antennas� Reflected antenna possibly very expensive
($1000+), should think of protecting it somehow
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University of Colorado
Questions?
The END