Experimental study on interferometric altimetry using a ground-based dual-antenna cGNSS-R

The direct and reflected signals can be concurrently received by both antennas of a conventional global navigation satellite system reflectometer (cGNSS-R) in ground-based settings. It is unfavorable for cGNSS-R carrier phase altimetry, but it also provides cGNSS-R the possibility of retrieving reflector height in the way of interferometric reflectometry. An initial ground-based water surface experiment was carried out to investigate the feasibility of cGNSS-R interferometric altimetry. GPS L1 C/A signals were received by an up-looking right hand circularly polarized (RHCP) antenna and a down-looking left hand circularly polarized (LHCP) antenna and then collected by a dual-channel sampler. The raw signals were postprocessed to generate their correlation power sequences. These sequences were then subjected to the GNSS interferometric reflectometry altimetry technique in order to estimate the LHCP antenna heights. Experimental results show that the correlation coefficients between the retrieved values and the true values are 0.77 and 0.95 for the RHCP antenna and the LHCP antenna, respectively. The mean absolute errors of the results are 0.15 m and 0.04 m, and the root mean square errors are 0.17 m and 0.04 m. It indicates that both the RHCP antenna and the LHCP antenna of a conventional GNSS reflectometer can be used for ground-based interferometric altimetry, and the LHCP antenna performs better in this openness-limited scenario.