I and Qs Simulation and Processing Envisaged for Spaceborne Polarization Diversity Doppler Radars

Abstract

The WInd VElocity Radar Nephoscope (WIVERN) mission concept, a candidate for ESA’s Earth Explorer 11 program, aims at globally observing vertical profiles of reflectivity and line-of-sight (LoS) winds in cloudy and precipitating regions. WIVERN uses a 94-GHz dual-polarization Doppler radar with conical scanning to address the limited coherence duration between radar transmitted from low-Earth satellites with small antennas. This system transmits closely spaced pairs of horizontally and vertically polarized pulses, which are better correlated than pulses of the same polarization separated by longer intervals. The polarization diversity pulse pair (PDPP) technique is then used to estimate radar observables such as reflectivities, differential reflectivities, Doppler velocities, and differential phase. This article introduces an efficient method for generating H- and V-I and Q time series from the covariance matrix of the autocorrelation function. This method treats the signal as a nonstationary stochastic process, making it suitable for the PDPP pulse sequence from a rapidly rotating antenna and more computationally efficient than inverse fast Fourier transform techniques. It also accounts for interfering cross-polar signals and decorrelation from the scanning antenna. This method is included in the mission’s end-to-end simulator, which processes data from raw I and Q to Level 1 estimates of polarimetric variables. For scientific applications, averaging at least 5 km (40 polarization diversity (PD) pairs) is necessary to reduce noise in polarimetric variables and Doppler velocities. Under optimal conditions, uncertainties at 5-km integration are 0.7 dB for reflectivities, 0.3 dB for $Z_{\text {DR}}$ , 0.4 m/s for Doppler velocities, and 1.9° for $\Phi _{\text {DP}}$ .