A delay/Doppler-mapping receiver system for GPS-reflection remote sensing

A delay/Doppler-mapping receiver system, developed specifically for global positioning system (GPS)-reflection remote sensing, is described, and example delay/Doppler waveforms are presented. The high-quality data obtained with this system provide a more accurate and detailed examination of ground-based and aircraft GPS-reflection phenomenology than has been available to date. As an example, systematic effects in the reflected signal delay waveform, due to nonideal behavior of the C/A-code auto-correlation function, are presented for the first time. Both a single-channel open-loop recording system and a recently developed 16-channel recorder are presented. The open-loop data from either recorder are postprocessed with a software GPS receiver that performs the following functions: signal detection; phase and delay tracking; delay, Doppler, and delay/Doppler waveform mapping; dual-frequency (L1 and L2) processing; C/A-code and Y-code waveform extraction; coherent integrations as short as 125 mus; navigation message decoding; and precise observable time tagging. The software can perform these functions on all detectable satellite signals without dead time, and custom signal-processing features can easily be included into the system. Data collected with this system can, in principle, be processed to extract 1) over an ocean: mean sea height, wind speed and direction, and significant wave height; 2) over land: soil moisture, biomass, and bistatic imaging; and 3) over ice: ice age, thickness, and surface ice density.