Demonstration of Bistatic Radar for Ocean Remote Sensing Using Communication Satellite Signals

Remote sensing of ocean roughness using reflected signals from digital communication satellites is demonstrated in an airborne experiment. Transmitted data are approximated as an infinitely long sequence of random bits, which is experimentally a hypothesis confirmed for the S-band XM radio signal. On July 2, 2010, a signal recorder was flown at an altitude of 3.17 km off the coast of Virginia, collecting ocean-reflected signals from both geostationary satellites identified as "Rhythm" and "Blues," which were broadcasting the XM radio signal. Direct and reflected signals from the same channel were cross-correlated, producing a waveform that agreed well with a model generated at the 7.5-m/s wind speed reported from the Chesapeake Lighthouse. Adjusting this model to fit the experimental data produced an optimal estimate of 6 m/s. A Monte Carlo approach predicted errors of 0.5% from the simulated reflected XM radio signals and 2%-10% from simulated reflected Global Navigation Satellite System (GNSS-R) signals. This improvement was attributed to the higher ( ~ 30 dB) power in the XM radio signal. The availability of communication satellite transmissions, in all frequency bands used for remote sensing, opens the possibility of using signals of opportunity as low-cost alternatives to radiometry or scatterometry.