Abstract
The NOAA Wide Swath Radar Altimeter (WSRA) and its processing are described. The WSRA provides real-time measurements of sea surface significant wave height and directional wave spectra during flights in hurricanes and other environments. The characteristics of near nadir scattering from the sea surface and the resulting distortion of the wave topography measured by the WSRA are discussed, as well as the simulation which generated a matrix to correct the directional wave spectra produced from the WSRA wave topography.
Highlights
H URRICANES draw energy through the air/sea interface, which is characterized by the directional wave spectrum
The volume of the antenna system and the vibration associated with the large oscillating mirror which scanned the beam could only be accommodated by a NASA research aircraft which did not fly in tropical cyclones, where knowledge of underlying ocean wave characteristics would be very valuable to the forecasters and weather modelers
The 180◦ ambiguity present when wave topography maps are transformed into directional wave spectra can generally be eliminated automatically in the vicinity of a hurricane by using a model to simulate the integrated forcing effect of the wind field
Summary
H URRICANES draw energy through the air/sea interface, which is characterized by the directional wave spectrum. The raw I&Q data are collected for the returns from sequential 150-MHz chirped transmissions on each of the 62 array elements These Level0 data, acquired over a 2–3-ms interval depending on the aircraft altitude, are coherently combined to produce 80 narrow beams spread over ±30◦ from the overall antenna boresight. WSRA MEASUREMENT GEOMETRY Fig. 2 (left) shows a grayscale-coded map of WSRA sea surface topography in Hurricane Irene on August 25, 2011, generated from the 64 beams nearest nadir for 500 raster lines of WSRA range data acquired as the aircraft flew northwest. Wave tilt modulation increases the apparent height of waves propagating across the swath and the effect is greater for shorter wavelengths
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