Computer Science
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........64m&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF WISCONSIN - MADISON, 1993.Source: Dissertation Abstracts International, Volume: 55-02, Sectio
Computer Science
Scientific paper
Evidence for a new approach to air/sea heat flux measurement is presented. The technique is based on radiometric determination of the air/sea interface temperature gradient. The water molecule's inherent radiometric characteristics cause variations in the absorption coefficient, allowing 2.0 -5.0 μm radiation to carry information about sub-surface water temperatures. Radiation leaving the surface is sensitive to water temperature in a layer centered at one optical depth (inverse of the absorption coefficient). Where atmospheric transmittance is high or the instrument is near the water surface, these radiance variations with frequency (i.e. optical depth) record temperature variations with depth. To measure these small radiance variations, an instrument must have low instrument noise and be radiometrically stable in suitable frequency bands. In computer simulations, spectra from an atmospheric model (US Standard Atmosphere 1976) and a water radiation model (assumed linear temperature gradient) were linked. The simulations showed that using this technique as a flux measurement is feasible with error that varied with instrument noise, low level moisture, sun angle and sea surface reflection coefficient. Flux magnitude RMSE rose from 17 W/m ^2 at the surface to 58 W/m^2 at 500 mb, showing negligible change for greater altitudes. Solar reflection has the strongest effect; precise knowledge of the reflection coefficient is required. Laboratory experiments showed spectral behavior which confirmed that the interface thermal structure can be studied in unprecedented detail. Water spectra showed strong temporal and thermal correlations between radiometric and independent heat flux measurements. Measured brightness temperature error cong 0.01 K. High spectral resolution (Deltanu = 1 cm^{-1}) gave 190 radiance measurements in 5 μm of water depth. It is concluded that a well calibrated high spectral resolution radiometer in the 2.0-5.0 μm region can sense information about the details of the interface thermal structure. This capability, useful in a variety of laboratory experiments, is suitable for heat flux measurement. Gas flux studies may benefit from examination of fine thermal structures in the uppermost 10 μm of water depth.
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