Contrast Attenuation Factors for Remote Sensing

Attenuation factors for the contrast of objects lying on the earth's surface and observed through five different atmospheric models are calculated as a function of the wavelength (0.31-0.9935 µm), solar zenith angle, ground reflectivity, and the nadir and azimuth angles of view. The first model is free of aerosols and absorbing gases. Absorption by average amounts of oxygen, ozone, and water vapor is included in the remaining four models. The second model is also free of aerosols, but the last three models contain aerosols in the form of a spherical polydispersion made from a substance with a spectrally independent refractive index of 1.5-0.01 i. Models 3 and 4 are expected to represent, respectively, the average and strong turbid conditions encountered over large continental areas. Models 3 and 5 contain aerosols with different size distribution characteristics, but have the same amount of aerosol mass loading per unit horizontal area. The contrast attenuation factor is found to increase with an increase in wavelength and reflectivity of the surrounding surface, and a decrease in the atmospheric turbidity and gaseous attenuation. It also depicts strong azimuthal dependence especially for models illuminated by low-altitude solar radiation of longer wavelengths.