Bi-directional Properties of Light Field of Inland Waters Based on Simulated Data by Hydrolight

To promote the study on the bidirectional reflectance properties of light field above inland waters, this paper took water quality parameters and inherent optical parameters measured in Taihu Lake as input, applied the radiative transfer model of Hydrolight to bidirectional ditribution of light filed of inland waters, and obtained the variation laws of bidirectional factors of Q and f/Q changing with observational direction and wavelength affected by driven elements. Results show that the f/Q variation with wavelengths is bigger than that of the observing zenith angle and observing azimuth angle. The f/Q variation with the observing zenith angle is bigger than the observing azimuth angle. The f/Q variation at blue and near infrared wavelengths is bigger than at green and red wavelengths. Among driving factors, solar zenith, suspended matter concentration, chlorophyll-a concentration, back-scattering probability of suspended matter, and cloud amount are the leading factors, which should be carefully treated when retrieving water quality parameters in turbid waters. Meanwhile, a _CDOM, back-scattering probability of chlorophyll-a, the ratio of downwelling diffuse irradiance to total downwelling irradiance, and wind speed can be ignored. In summary, when retrieving water quality parameters and only considering the influence of bi-direction properties, the remote sensing reflectance should be chosen at green and red wavelengths, with the observing zenith angle within 40°, observing azimuth angles of 0°-150° or 210°-360°, which will reduce the errors aroused by multi-angular observation, and promote the inversion accuracy of water quality parameters.