Estimation of Sea Surface Temperature from Remote Sensing in the 3.7μm Window Region

Abstract

The diffusely reflected radiation in the daytime and diffusely transmitted radiation at night from an inhomogeneous, plane parallel planetary atmosphere bounded by the ocean surface was calculated at the 3.7μm infrared window region. In the daytime the effect of the solar radiation from top was taken into account. This spectral region corresponds to the channel 3of the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA-6 satellite. Thus the deviation from the sea surface temperature (SST) was evaluated in the mid-latitude region in summer, where it is defined by the difference between the given surface temperature and the calculated brightness temperature obtained at the top of the atmosphere. The present study has dealt with the problem of no cloud contamination in data. In the atmosphere, water vapor, molecular nitrogen, nitrous oxide, carbon dioxide and methane as absorbent constituents and aerosols as the scattering constituent were taken into account. The ocean surface as a lower boundary was simulated by many facets whose slopes are according to the isotropic Gaussian distribution (Cox and Munk, 1955). The slope of the facet depends upon the ocean surface wind. The refractive index of the ocean surface as well as the aerosols in the atmosphere is assumed to be that of water by Hale and Querry (1973).
Computational results show that it is suitable for deriving the optical thickness in the direction of about 15° away from the specular direction. Hence the ocean surface temperature can be evaluated with the aid of the optical thickness thus derived, whereas the influence of the atmosphere to SST can not directly be estimated by the use of single channel of 11μm window region. On applying this result to the NOAA-AVHRR data (30°N, 147°E) on Aug. 2, 1979 together with the wind speed reported by ship, the very clear atmosphere simulates SST within the accuracy of 1-2°K at the center of the sunglint and within the accuracy of 0.5°K in the rest of the region. This atmospheric condition agreed with the ship data of visibility. To discuss the accuracy further, comparison of the radiometric measurements of SST by ships with temperature measured by satellite is essential.