An Unbiased Multiparameter Algorithm of Retrieving Sea Surface Height Using Coastal GNSS Reflectometry

Due to the diffuse scattering on sea surface and dynamic geometry of coastal global navigation satellite system-reflectometry, the altimetry performance is strongly dependent on elevation angle. As the elevation angle decreases, the bias in retrieved height using the peak of the derivative waveform and the fractional power point of the waveform leading edge increases. In this article, a multiparameter estimator is proposed to combine the peak of the derivative waveform and several fractional power points to obtain unbiased height. The simulated results show that the bias of the uncalibrated height using the proposed algorithm has no significant dependence on elevation angle, but the standard derivation for the low elevation angle case still is larger than that of the high elevation angle. In addition, the calibrated performance depends on the used fractional values so that proper fractional values should be chosen. The data from the Dongying experiment acquiring GPS L1 CA and L5 signal and the Qingdao experiment for BeiDou B1I signal are used to demonstrate the proposed algorithm. After calibrating using the proposed algorithm, regardless of GPS L1 CA, L5, or BeiDou B1I signal, the calibrated heights all are in agreement with in situ heights. Finally, the calibrated heights from the BeiDou B1I signal are used to retrieve sea surface height. The results show that retrieved sea surface heights from geostationary Earth orbit (GEO) and inclined geosynchronous orbit/middle Earth orbit (IGSO/MEO) satellites all appear in the same trend as that of the in situ ones; furthermore, GEO satellites can provide a better retrieved performance than IGSO/MEO satellites. Through averaging the heights from several satellites and smoothing with the half-hour span, compared to in situ sea surface height, the standard derivation of 0.67 m is obtained.