Removal of atmospheric effects on a pixel by pixel basis from the thermal infrared data from instruments on satellites. The Advanced Very High Resolution Radiometer (AVHRR)

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Abstract
This paper is concerned with those values of sea-surface temperatures which lie between 270 and 300 K. The thermal infrared (THIR) data under consideration are from the 3-7, II and 12μm channels of the Advanced Very High Resolution Radiometer (AVHRR) instruments on TIROS-N, NOAA-6 and 7 satellites. Simple relations for calculating the brightness temperatures from the THIR channels of the AVHRR are derived. Algorithms are presented for correcting these brightness temperatures for the non-linear response of the detectors used in the 11 and 12μm channels and for the emissivity of sea-water. Assuming the emissivity of sea-water is equal to 0.98, it is shown that, say, at 290 K. the emissivity corrections are about 0.45, 1.27 and 1.37K, respectively, in the 3.7, 11 and 12 μm channels. For comparison purpose, we have included a brief account of the atmospheric correction procedure' which is intended to be employed for correcting the thermal infrared data from the European Remote Sensing satellite, ERS-1, in the late 1980s. Using the standard atmospheric transmittances which were calculated by Phulpin and Deschamps (1980) we have developed a simple procedure for applying atmospheric corrections to the Advanced Very High Resolution Radiometer data using two spectral channels. This atmospheric correction procedure (i) does not require a knowledge of the distribution and abundance of the absorbers, emitters and scatterers in the atmosphere, and (ii) still enables one to evaluate the effective transmittance of the atmosphere which lies within the instantaneous field of view of the remote sensor. This means that one can apply the atmospheric correction on a pixel by pixel basis. An algorithm for the determination of the sea-surface temperature (SST) from the satellite data is presented. This algorithm utilizes the 11 and 12μm channel data from the NOAA-7 satellite. The reliability of this algorithm has been tested. Comparison of atmospherically corrected SSTs with the simultaneous in situ bulk and point temperature data set (17 points) for relatively cloud-free atmosphere resulted in a bias of 0.63 K and a root mean square difference (r.m.s.d.) of ±0.69 K. When the algorithm for SST determination was corrected for this bias then the r.m.s.d. reduced to ±022 K.

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