A wideband passive synthetic-aperture multichannel receiver (20) with an antenna (15) is mounted on a satellite 10 which travels in an orbit above the Earth passing over large bodies of water (12) e.g. the Atlantic Ocean. The antenna is scanned (16) to receive signals over a wide frequency band from each incremental surface area (pixel) of the water (P1, P2, etc.) which are related to the pixel's sea temperature. The received signals are fed to a plurality of channels (C1-C10) which are tuned to separate selected frequencies (f1-f10). Their outputs are fed to a processor (25) with a memory (30) for storage therein. As the antenna points to pixels (footprint FP 1-1, etc.) within a calibration area (A1) around a buoy (B1) of known coordinates, signals are likewise received and stored. From the buoy exactly measured sea temperature is received. After passing over several calibration areas, a forward stepwise regression analysis is performed to produce an expression which selects the significant from the insignificant channels and assigns weights (coefficients) to them. The expression is used to determine the sea temperature at each pixel based on the signals received therefrom. Wind temperature, pressure, and wind speed at each pixel can also be calculated.
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