University of Colorado

GPS as a remote sensing tool

Stephan Esterhuizen

Colorado Center for Astrodynamic Research

University of Colorado2006

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

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

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

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

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

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)

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

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

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

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)

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

University of Colorado

Questions?

The END