Methane seepage is indicative of petroleum or natural gas reserves. Techniques aimed at detecting methane seepage with surface-based instrumentation have progressed significantly in recent years. These techniques rely on measurement of light attenuation due to methane absorption of short wave infrared (SWIR) radiation. Detection of methane seepage over water bodies with electro-optical remote sensing has been limited by the low surface reflectance of water. Also, due to sensor saturation, imagery over sunglint is commonly discarded in satellite remote sensing, because the glint conditions produce high surface reflectance. However, recent measurements in the SWIR of sunglint regions have revealed that the surface reflectance is spectrally flat and enhanced without causing saturation. This higher surface reflectance in sunglint regions allow for retrieval of the total column methane amount using ratios of measured radiances at wavelengths inside and outside the methane SWIR-absorbing channels. The methane retrieval method presented here, based on shortwave infrared band ratios in sunglint regions, allows for detection of methane seepage over the Earth's oceans and lakes, and the detection of possible petroleum or natural gas reserves. Radiative transfer simulations are used to demonstrate the capabilities offered by this technique.
Radiance multiply scattered from clouds and thick aerosols is a significant component in the short wave IR through the visible region of the electro-optical (EO) spectrum. In MODTRAN, until very recently, multiple scattering predictions could not vary with the azimuth of the line-of-sight (LOS), although the single scattering component of the radiance did take the azimuthal variation into account. MODTRAN has now been upgraded to incorporate the dependence of multiple scattering (MS) on the azimuth of the LOS. This was accomplished by upgrading the interface between MODTRAN and DISORT, which is used as an MS subroutine in MODTRAN. Results from the upgraded MODTRAN are compared against measurements of radiance in a cloudy sky in the 1.5 - 2.5 micrometer region. Furthermore, taking advantage of DISORT, the upgraded version of MODTRAN can accommodate parameterized BRDFs (Bi-Directional Reflectance Distribution Functions) for surfaces. Some results, which demonstrate the new MODTRAN capabilities, are presented. Additionally, MS results from MODTRAN are compared to results obtained from a Monte-Carlo model.