Based on a developed three-layerair–ice–water reflection model, this article simulates the evolution of reflection coefficient versus elevation angle. Due to the interference between the signal components from the air–ice and ice–water interfaces, the reflection coefficient experiences an oscillating pattern versus elevation angle so that detecting sea ice using the power or amplitude of the reflected global navigation satellite system (GNSS) signal has to choose a suitable satellite to reduce the influence of the oscillating pattern. A sea ice surface is more stable and presents higher correlation than a dynamic ocean surface, this article explores the potential of detecting and measuring sea ice using the coherency of reflected GNSS signal for coastal scenario. Experimental results show that phase coherency can significantly detect sea ice without strictly limiting elevation and azimuth angle. This article also is to is to explore the potential of retrieving sea ice thickness using the oscillating phase pattern versus elevation angle. The phase compensation and the dual-polarization observation are proposed to remove the delay phase between the direct and reflected signal from the estimated phase of the reflected GNSS signal. The results show that the amplitude and frequency of the oscillating phase pattern, respectively, have an inversely proportional and positively linear relationship with sea ice thickness. Simulation shows that, compared to the oscillating amplitude, the oscillating frequency is a better choice to measure sea ice thickness. The frequency of the dual-polarization oscillating pattern could provide the measurement performance with a root-mean-square error of 0.05 m.

The Global Navigation Satellite System Pseudo Interference Reflectometry (GNSS-PIR) is proposed for ground-based soil moisture remote sensing in this letter. It combines the signal received by the up-looking right-hand circularly polarized (RHCP) antenna with that received by the down-looking left-hand circularly polarized (LHCP) antenna to form an oscillatory carrier to noise ratio (CNR) waveform. The analyses of waveform quality and parameters' sensitivities to soil moisture in comparison with GNSS Interferometric Reflectometry (GNSS-IR) indicate that both the amplitude and the phase of GNSS-PIR waveform at high elevation angles are available for soil moisture determination. Soil moisture inversion based on Monte Carlo simulations shows that GNSS-PIR obtains better inversion accuracy than GNSS-IR.

Due to the diffuse scattering on sea surface and dynamic geometry of coastal GNSS- R, the altimetry performance is strong dependent on elevation angle. As elevation angle decreases, the bias in retrieved height using DER and HALF retracker increases. In this paper, an multi-parameter estimator is proposed to combine the DER retracker and several HALF retrackers to obtain unbiased height. The simulated results show that the bias of the uncalibrated height using proposed algorithm has no significant dependence on elevation angle, but the RMSE for the low elevation angle case still are 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 Dongying experiment acquiring GPS L1 CA and L5 signal and Qingdao experiment for BeiDou B1I signal are used to demonstrate proposed algorithm. After calibrating using proposed algorithm, regardless of GPS L1 CA, L5 or BeiDou B1I signal, the calibrated heights all are agreement with in-situ heights. Finally, the calibrated heights from BeiDou B1I signal are used to retrieve sea surface height. The results show that retrieved sea surface heights from GEO and IGSO/MEO satellites all appear the same trend with in-situ ones, furthermore, GEO satellites can provide the 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 RMSE of 0.67 m is obtained.

For spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R), the delay difference of direct and reflected GNSS signals among successive snapshots changes rapidly because of the high dynamics of low earth orbital and GNSS satellites. This change has to be compensated to avoid the distortion of incoherently averaged delay-Doppler map (DDM). The method to refresh the correlation window on each coherent integration time period may require too many instrument resources or too much data to be uploaded from the ground station. This letter proposes a new postprocessing approach based on the motion degradation model of DDM and the reconstruction to replace real-time compensation. Raw sampled data from UK TechDemoSat-1 are used to verify the availability of proposed approach. The results show that after reconstruction for the distorted DDM, the DDM accuracies relative to that compensated in real time are significantly improved.