6. Water-Surface Wind Retrieval Using Airborne Radar Altimeter

Radar altimeters are frequently used by aircraft. The primary function of the Airborne radar altimeter (ARA) is to provide terrain clearance or altitude with respect to the ground level directly beneath the airplane or helicopter. The ARA may also provide a vertical rate of climb or descent and selectable low altitude warning. Typical scatterometer wind measurements are commonly performed using antennas with comparatively narrow beams. As the ARA has a wide-beam antenna, the beam sharpening technologies should be used to apply the ARA for wind vector measurement. For that prepuce, Doppler discrimination along with range discrimination have been employed. The wind retrieval algorithms for several particular beam geometries are presented. The study has shown that wind vector over sea can be measured by means of the ARA employed as a nadir-looking wide-beam short-pulse scatterometer in conjunction with Doppler filtering. The measuring instrument should be equipped with two additional Doppler filters (a fore-Doppler filter and an aft-Doppler filter) to provide for spatial selection under the wind measurements.