Analysis of the correlation properties of digital satellite signals and their applicability in bistatic remote sensing

This paper presents a study of relevant correlation properties of signal transmitted from commercial communication satellites in order to evaluate their potential use as “signal of opportunity” for bistatic remote sensing. The ambiguity function for the XM radio satellites was computed analytically from published information on the modulation schemes and bandwidth, under the assumption that the data modulation is random. The model was then experimentally tested by recording the received signals from these satellites. Next, a cross-correlation waveform for digital signal reflected from random rough surface was simulated. Scattering model that were originally developed for Global Navigation Satellite System (GNSS-R) signals was applied to the modified simulator to incorporate the derived ambiguity function. The simulator was then used to generate synthetic waveform with a realistic signal to noise ratio (SNR). Retrieval algorithms for ocean surface roughness and reflectivity that were derived originally for GNSS-R, were applied to these simulated signals. Non-linear least square methods were applied to invert a scattering model and estimate the slope variances of the probability density function (PDF), which best fits the measurements of the reflected XM signal waveform. The SNR for the experimental data was found to be within 0.5dB of the theoretically calculated SNR.