Along-Track Focusing of GNSS-R Coherent Signals

An architecture for GNSS-R coherent data processing is here proposed. This scheme is similar to range-Doppler Synthetic Aperture Radar (SAR) focusing and is applicable to coherent GNSS-R data in order to increase along-track spatial resolution. Starting from the model defined in [1], the approach is introduced in Section 2 and then studied in Sections 4 and 5. In the simulation setup in Section 5, the acquisitions are modeled using a GNSS-R discretized scenario, with 20 m spacing among scattering cells. The simulated scene is composed by a homogeneous background, having a reflection coefficient 0.9, in which two separate regions are set, having a circular shape with a 200 m radius and a reflection coefficient equal to 0.1. Simulations confirm that the along-track resolution is improved by signal focusing. As derived in Section 4, using a 100 ms coherent integration time, the along-track resolution is about 150 m, whereas the range resolution is limited by the scattering regime, in any case much smaller than the resolution due to the ambiguity function [12].