Revisiting the Interferometric Complex Field and Constructing a Novel Processing Scheme for Monitoring Sea States From Coastal GNSS Reflectometry

This paper revisits the Interferometric Complex Field (ICF) concept in coastal Global Navigation Satellite System-Reflectometry (GNSS-R), and proposes a novel baseband signal processing scheme for monitoring sea states. The scheme utilizes incoherent averaging to reduce hardware complexity while maintaining accuracy comparable to correlation-based methods. This eliminates requirements for the RHCP antenna, RF front-end, and baseband processor of the direct signal. Compared to the existing schemes, it has lower computational complexity, power, and cost. The primary observable, termed the alternating-current incoherent average power (aIAP), is derived by detrending a stable baseline component from the output of the proposed scheme. The coherence time and spectral width from the aIAP time series are defined as the observables of retrieving sea state, specifically wind speed and significant wave height (SWH). Three experimental data sets are used to demonstrate and assess the proposed scheme. Results indicate that the coherence time and spectral width of aIAP exhibit sea-state dependencies similar to those of alternating ICF within a wind speed range of 0 ∼ 15 m/s, and thus can be used to retrieve sea state. Spectral width retrieves sea state more effectively than coherence time. Coherence time and spectral width weakly depend on elevation angle so that an elevation correlation is unneeded. The proposed scheme, as a cost-efficient alternative, has the potential for operational sea state monitoring.