ИСТИНА

In this study, the bias effect has been investigated both experimentally and theoretically. The re ections of radio waves of navigational space-borne radio beacons from undulating sea surface have been simulated numerically. Electromagnetic field at the main frequency of the Global Positioning System (GPS) L1 (1575.42 MHz) has been evaluated 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 re ected waves of GNSS is effectively observed with a single antenna. The simulation predict that the bias of measured sea level is proportional to the surface wave height. Verication of this theoretical conclusion on the experimental data shows that for low and moderate wave prole heights (not exceeding the radio wave length) this systematic bias and the wave prole height are indeed proportional. Further increase of the wave prole 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.