[Observation and simulation of bi-directional spectral reflectance on different type of soils]

Knowledge of radiative transfer over bare soils is a prerequisite to addressing vegetation canopies and predicting soil properties by remote sensing. In the present study, the change in the spectral reflectance for three soils (i. e. red soil, paddy soil and coastal saline soil) with different view zenith and azimuth angles in the visible band (620 nm) and Landsat TM4 near infrared wavebands (760-900 nm) was measured in laboratory. The results showed that soil reflectance increased with increasing off-nadir view angle for all azimuth directions and soil bidirectional reflectance was azimuthally symmetric. The reflectance was highest in backscattering direction and lowest in forward-scattering direction. The bidirectional reflectance was simulated well using the Hapke model derived from the radiative transfer theory. The root mean square errors (RMSE) were 0.003, 0.002 and 0.004 and the correlation coefficients were 0.995, 0.998 and 0.998 in simulating bidirectional reflectance in visible wavebands for red soil, paddy soil and coastal saline soil, respectively; RMSE were 0.004, 0.006 and 0.005 and the correlation coefficients were 0.997, 0.996 and 0.998 in simulating bidirectional reflectance in NIR wavebands for these soils, respectively. It is stated clearly that Hapke model could be used to simulate the whole spectra curve, then to retrieve the soil surface characteristics.