ИСТИНА

Inteferometric reflectometry is a relatively cheap technique for in situ measurements of the sea level surface, which can be implemented both at coastal stations of geodetic Global Naviational Satellite Systems (GNSS)-networks and specially organized observatories of global environmental monitoring. This technique, however, suffers from errors caused by sea surface perturbations. Surface waves are probably the most important source of random and systematic biases in the measured data. In this study, the technique of reflectometric altimetry of the local sea level is investigated both experimentally and theoretically. The reflections of radio waves of navigational space-borne radio beacons from undulating sea surface have been simulated numerically with the Finite Difference in Time Domain (FDTD) technique for different model spectra of the sea waves. Impact of the surface waves on the mean sea level estimate at the monitoring station location is investigated for low wave grazing angles, at which the interference between direct and reflected waves of GNSS is effectively observed with a single antenna. The simulation predicts that the bias of measured sea level is proportional to the surface wave height. Verification of this theoretical conclusion on the experimental data shows that for low and moderate wave profile heights (not exceeding the radio wave length) this systematic bias and the wave profile height are indeed proportional. Further increase of the wave profile height destroys the interference pattern, which prevents surface echo detection and estimate of the sea level. Nevertheless, for moderate surface waves the sea level measurements can be corrected for the bias effect, if the surface waves are independently registered and recorded.