CCAR / University of Colorado 1 Airborne GPS Bistatic Radar in CLPX Dallas Masters University of Colorado, Boulder Valery Zavorotny NOAA ETL Stephen Katzberg NASA LaRC

CCAR / University of Colorado 2 Review of GPS Bistatic Radar CLPX 02 & 03 was first piggyback test of GPS bistatic radar over snow and mountainous terrain Uses simple, modified GPS receiver to measure signals scattered from the land surface Receives GPS L-band 1.5 GHz Bistatic radar measures forward scattered power rather than back scattered power; functions as a scatterometer Antennas: Zenith RCP hemi patch for direct signal tracking, navigation Nadir LCP hemi patch (wide field) for reflected signal measurement Footprint is range-limited by GPS pseudo-random code, but land surface may look “specular” for smooth to moderate roughness

CCAR / University of Colorado 3 GPS Bistatic Radar Geometry Rough surface glistening zone Range cells GPS Transmitters 24 sats L1: 1.5, L2: 1.2 GHz PRN coding Direct Signal RCP Reflected Signal LCP GPS Receiver Zenith & nadir antennas Specular point

CCAR / University of Colorado 4 Bistatic Radar Measurement GPS bistatic radar measurements: Delay of reflected signal  receiver height above surface Magnitude of reflected power  reflectivity  water content Distribution of reflected power  surface roughness  Delay (range) Delay (Altimetry) Reflected Signal Direct Signal Bistatic crosssection (Soil Moisture) Correlation Power Increasing Roughness Delay (range) Delay (Altimetry) Reflected Signal Direct Signal Bistatic crosssection (Water Content) Correlation Power Increasing Roughness Specular point

CCAR / University of Colorado 5 CLPX03 Configuration Delay mapping receiver (DMR) developed by Katzberg & Garrison (NASA LaRC), based on GEC-Plessey GPSBuilder2 5 channels operate in a nominal zenith tracking mode 7 channels operate open loop, measuring the scattered power at specified chip offsets with respect to the direct signal Operates autonomously w/ PC-104 Size: 20x15x15 cm chassis Flew on NASA P-3 Collected measurements: 02/21,23,24; 03/25,30,31 Aircraft height at ~5000 m AGL Auto selection of highest elevation sat (nearest nadir incidence) Incidence angles between 0-35 deg Footprint size varies: Fresnel zone ~ 80 m to 3 km depending on specularity of reflection and receiver height

CCAR / University of Colorado 6 GPS Bistatic Radar Instrument Rackmount PC-104 GPS receiver LCP patch antenna

CCAR / University of Colorado 7 GPS Bistatic Radar Flight Typical GPS reflected signal flight lines ( ) Lake calibration Low altitude area Latitude Longitude SNR (dB)

CCAR / University of Colorado 8 CLPX03 Reflections/NP MSA Low altitude area Typical GPS reflection 1 sec waveforms showing quasi-specular and rough surface scattering SNR transect of NP MSA showing reflectivity variations

CCAR / University of Colorado 9 CLPX03 Reflections/Frasier MSA Lake calibration Low altitude area Reflected SNR correlated with surface elevations

CCAR / University of Colorado 10 Working with GPS Bistatic Radar GPS measurements should be considered EXPERIMENTAL Calibration issues: GPS receiver is uncalibrated in absolute sense Assume noise is constant and estimate SNR Assumptions for first order analysis: Surface roughness, incidence angle, receiver height constant Estimate reflected SNR Maps of SNR tracks sensitive to surface Fresnel reflectivity and roughness Need to compare with other data sets, imagery

CCAR / University of Colorado 11 CLPX GPS Summary Collected data sets in 02 and 03 campaigns Reflected signals were quasi-specular First-order reflectivity maps show spatial variations of reflectivity CLPX data sets: Ground tracks georeferenced to EGM96/GTOPO30 (1km) surface model Parameters of interest: reflected SNR, direct SNR, waveforms satellite parameters, aircraft parameters Data sets available by day in HDF format (~30MB/day) Data available directly from or through a link at NSIDC