Wide-band radiometry for remote sensing of oil films on water

Total-power radiometry is applied over a wide-frequency band (26-40 GHz) to measure homogeneous and emulsified (40%:60% oil:water composition) oil fil ms on water. The resulting brightness-temperature (T-B) spectra contain sub stantially more information about the film than the spot-frequency measurem ents of previous work, In thin homogeneous films (similar to 3 mm Or less), the T-B spectra have the same monotonically increasing frequency dependenc e as the bare water spectrum, but are distinguishable from the water by a p ositive T-B offset, For thicker homogeneous films, oscillations in the T-B spectra occur that have a period inversely related to the thickness of the film. For emulsified films, the T-B offset is greater than that of a homoge neous film of the same thickness, and oscillations in T-B occur, even for t he thinnest (1 mm) emulsion tested, However, the amplitude of these oscilla tions is much smaller than for homogeneous films because of losses in the e mulsion, Hence, the key result of this paper is that wide-band radiometry e nables both the unambiguous determination of the thickness of homogeneous o il and the discrimination of homogeneous oil from emulsified films, at leas t in the range of thickness >1 mm.