Study And Application Of Canopy BRDF Model

In the recent years, with the development of optical remote sensing technology, it is impossible to obtain the agricultural information means by a large scale. But there are some difficulties in practical applications, so it cannot reach the precision we respect. One reason is the study of physical model of canopy BRDF yet not deep enough. Through the study of the BRDF model, we can strengthen the understanding of contact between canopy structures parameters, biochemical component and BRDF(Bidirectional reflectance distribution function ) of canopy and promote the application of the optical remote sensing technology on agriculture.In this paper, development state of physical model of canopy and model inversion is introduced. This paper introduced canopy BRDF model which is better suited for canopy of wheat on Radiative Transfer Model. This model includes FCR model, PROSPECT model, ellipsoidal model and solar altitude model.Precision of the PROSPECT and FCR model is validated by comparing simulations made by using PROSPECT and FCR model and actual investigation. And it analysis the cause of the error.As BRDF model used in this paper were established on some assumptions, there always exist some differences between the simulated data and the measured data. When using the model to invert the canopy structures and biochemical component parameters, the accuracy will be decreased if we use all measured data without distinguishing them. This paper presents a multi-stage inversion method, using least median of squares( LMS) and least-squares( LS). It has demonstrated that, toward the measured data which have some errors or cannot be simulated by the model, this approach is robust to estimate the parameters.