Modeling and Analysis of Delay Doppler Maps for Spaceborne GNSS-R Signal Scattered from Sea Surface

The Global Navigation Satellite System Reflected (GNSS-R) Signal adopts a heterogeneous observation mode and utilizes the globally shared GNSS constellation as a multisource microwave signal transmission source, providing the opportunity signals for radar measurements. As a basis for GNSS-R bistatic remote sensing simulations, this paper analyzes wave spectrum model of sea surfaces, GNSS signal scattering model, and GNSS signal scattering power model. The modified Zavorotny and Voronovich (Z-V) model combined with two-scale method (TSM) for sea surface scattering is utilized to simulate the delay Doppler map (DDM), with emphasis on the analysis of the effects of wave polarizations, delay Doppler interval, and sea states on DDM of GNSS signal scattered from sea surfaces. The correlated power model of GNSS scattering signal is validated by comparison with measured Cyclone Global Navigation Satellite System (CYGNSS) DDM data in L1 level 2.1 version. The DDM waveforms obtained from Z-V model combined with TSM are basically consistent with the CYGNSS actual data, in which the strong scattering spots can be observed clearly from both simulated and measured DDM. Modeling and analysis of DDM for spaceborne GNSS-R signal from sea surface is of great value in ocean remote sensing applications, in particularly for the interpolation and utilization of various spaceborne GNSS measured data.