Methodical Errors of a High-Precision Airborne Radio Altimeter Operating at Low Altitudes Above the Sea Surface

Abstract

When a high-precision airborne radio altimeter operates at low altitudes in the mode of measuring the sea-surface profile, the local time-dependent backscattering pattern is a characteristic of the reflecting properties of the sea surface in contrast to the majority of other cases where the irradiation spot is significantly greater than the typical sizes of the large-scale surface irregularities. In this case, the altitude estimate at the tracking-system output of the flying-vehicle radio altimeter is the sum of three terms, namely, the altitude to the mean level, the altitude-estimate shift, which varies in time as a function of the slopes of large-scale irregularities, and the component related to the surface topography. The current methodical error of the altitude estimation by the high-precision airborne radio altimeter at low altitudes can be calculated using the justified approximation of the sea-surface large-scale irregularities by a deterministic function.