The effect of viewing geometry and wavelength on the relationship between reflectance and suspended sediment concentration

Abstract

The relationship between reflectance and suspended sediment concentration (SSC) is dependent upon the wavebands sensed and the viewing geometry of the sensor. The laboratory experiment reported in this paper investigated these dependences. The reflectance in four wavebands (two visible and two near-infrared) of a large water-filled and wave-free tank were recorded as three variables were changed, namely SSC, sensor viewing angle and relative sensor azimuth. The strength of the positive relationship between reflectance and SSC was shown to vary with (i) wavelength, as the maximum reflectance and SSC class separability occurred at the longer visible wavelengths, and (ii) viewing geometry, as the reflectance/SSC asymptote was dependent upon both the angle and azimuth of the sensor. The optimum conditions for the sensing of SSC were concluded to be nadir in visible (0·55 and 0·65 μm) and near-infrared (0.75 μm) wavelengths.