A Matched Filter for Spaceborne GNSS-R Based Sea-Target Detection.

The motion of any potential sea-targets in a sequence of delay Doppler maps (DDMs) collected by a spaceborne global navigation satellite system-reflectometry (GNSS-R) receiver can be computed as a priori information due to the receiver velocity dominating that of any realistic sea-targets. This can be exploited to design a matched filter to detect sea-targets in a DDM sequence without the requirement for any (pre)detection and can be considered a track-before-detect technique. In this article, such a filter is developed and applied to DDMs collected by TechDemoSat-1, and the detection of sea-ice is demonstrated. A frequency analysis of simulated and actual DDM sequences containing a sea-target is carried out. We show that the stationary sea-clutter is bound to the zero time–frequency plane in the 3-D frequency response of the DDM time series, while only $\approx $ 13.8% of the target’s energy is located in this plane. This finding motivates the application of an adaptive whitening filter to blindly suppress the temporally correlated clutter in the DDM sequence before applying the matched filter to the prewhitened sequence containing a spatially fixed point-like response arising from the edge of an ice sheet, which is equivalent to a point-like sea-target such as a ship. This results in a signal-to-clutter ratio of $\approx $ 12 dB being achieved when processing only the weak target responses at nonspecular locations originating from the spatially fixed edge of the ice sheet. This is the first technique to exploit the delay and Doppler dynamics of a target to obtain a coherent integration gain. [ABSTRACT FROM AUTHOR]