Bi-directional Reflectance Distribution Function (brdf) Retrievals from Laboratory Multiangle Measurements

Theoretical investigations and intense experimental activity have being devoted to study the geometrical properties of reflection from a surface, that is expressed in terms of Bi-Directional Reflectance Distribution Function, a quantity that is relevant to many remote sensing applications, such as atmospheric modelling and climatologic studies. A large amount of laboratory and in-field measurements are now available from various systems such as the European Goniometer Facility of the Joint Research Centre, the Field Goniometer System of the University of Zurich, and the Portable Apparatus for Rapid Acquisition of Bidirectional Observation of Land and Atmosphere instrument of NASA – GSFC. Moreover, recent satellite missions such as the Multi-angle Imaging SpectroRadiometer and the Compact High Resolution Imaging Spectrometer on board of EOS-AM1 and PROBA platforms supply experimental data to this research. Following this general trend aimed to improve the current understanding of directional properties of reflection from a surface, we present laboratory multiangular observations of natural sands. These data are used in conjunction of literature data to study the reflectance dependence on surface optical and mechanical properties, illumination and viewing geometry. A simple empirical model is developed in order to retrieve Bi-Directional Reflectance Factor from experimental data. Finally, the possibility to extend the proposed physical model even to remotely sensed data is discussed, with particular reference to images gathered with CHRIS spectrometer. where the denominator indicates the total irradiance impinging on the concerned target at angle ( , the reflected radiance collected by the sensor in the direction . ) , 0 0 φ θ ) , , , , ( 0 0 v v s L φ θ φ θ λ ) , ( v v φ θ