This paper introduces the process of theoretical prediction of brightness temperature and the analysis of the brightness temperature observed from aircraft, taking into account aircraft attitude and radiometric corrections. Microwave radiometric observations were made from aircraft at the two heights of 300 and 2000m above the sea level in Kii Strait in November 10-12, 1987. Microwave frequencies used are 6.7 and 18.6 GHz. The beamwidths of the two radiometers employed are about 9 degrees. Observed brightness terperature was, at first, compared with the theoretically predicted one which is an averaged brightness temperature over the boresight beamwidth of 30 degrees and is only due to sea surface emission (free from surface reflection and sky radiation). The former was larger than the latter over entire angular range of incidence in both polarizations at both frequencies. Next, the observed brightness temperature was compared with the theoretically predicted one, considering radiations coming from all directions, i.e. the sea surface and the sky. The sea surface reflection of the downwelling sky radiation was also considered. This correction leads to good agreement between observation and theoretical prediction, and the surface reflection is of significant effect to the observed brightness temperature. Finally, main-lobe-averaged brightness temperature only due to the inherent sea surface emission was also retrieved from the observed one, incorporating the surface reflection and side lobe effect corrections. The retrieved results agreed with the theoretical predictions. The retrieved results agreed with the theoretical predictions within 3K over entire incidence angle in both polarizations at both frequencies.
Possible techniques for lithologic discrimination using spectral bands in the short wavelength infrared (SWIR; 1.3-2.5, μm) region have been tested. Image data of Queensland, Australia, obtained by Geoscan AMSS (Airborne MultiSpectral Scanner) MkI were used in this study. As this scanner has quite similar spectral band characteristics to the optical sensor of the JERS-1 (Japanese Earth Resources Satellite), which is scheduled to be launched in 1992, the techniques proposed for the JERS-1 data were applied to the AMSS MkI data. The proposed techniques enhance inter-band response patterns in reflectance space, so that it is necessary to convert original digital numbers (DN) to reflectance of surface materials. The linear regression method using field reflectance measurements could not be applied in this case, because it was difficult to find good calibration targets in the study area. Instead, the Log Residual technique, which normalizes the DN values using geometric means of each pixel and each band, succeeded in converting DN values to band responses resembling to reflectance patterns. Two spectral indices; Alunite Index (ALI) and Calcite Index (CLI), were calculated by linearly combining the three SWIR bands normalized by the Log Residual method. The Perpendicular Vegetation Index (PVI) was also calculated using two visible and near infrared bands. The images of these spectral indices successfully showed an epidote-rich zone, sericite-rich zones in hydrothermally altered areas, and distribution of vegetation. These techniques have the advantages that the processed results can be easily interpreted by a geologist for the purpose of lithologic discrimination.