Airborne measurement of the sea surface wind speed by a scatterometer (altimeter) having a nadir-looking wide-beam antenna

A pilot needs operational information about wind over sea as well as wave height to provide safety of hydroplane landing on water. Near-surface wind speed can be obtained with an airborne microwave scatterometer radar designed for measuring the scatter characteristics of a surface. Narrow-beam antennas are applied for such wind measurement. Unfortunately, a microwave narrow-beam antenna has considerable size that hampers its placing on flying apparatus. In this connection, the influence of antenna beamwidth expansion on the result of measurement of the sea surface NRCS by a scatterometer (altimeter) having a nadir-looking wide-beam antenna was researched. The expression for the measured NRCS, taking into account the antenna beamwidth and the variation of the sea surface slope, was obtained, and the measuring algorithm of the sea surface wind speed was proposed. The obtained results can be used for creation an airborne radar system for operational measurement of the local wind situation over sea and for safe landing of a hydroplane on water.