Global Mapping of Bidirectional Reflectance and Derived Surface Parameters for the EOS MODIS Project

As spectroradiometers that can view the Earth’s surface from numerous angles become available (i.e., NASA’s MODIS and MISR instruments of the Earth Observing System), global mapping of land surface bidirectional reflectance becomes feasible. The BRDF/Albedo product for EOS-MODIS uses many models from purely empirical to physical, from radiative transfer-based to geometric optics-based to map bidirectional reflectance regularly on a global scale, to deduce from the observations surface albedo, and sometimes to obtain information about land surface geometric structure (or plant canopies covering it) through inversion of the models.

This information will be needed as input into the next generation of climate change, mesoscale meteorology and surface energy budget models, especially since the retrieved surface parameters may in many cases allow to infer surface roughness.

The model type used for each pixel is chosen based on the following: a) the type of scene expected, as deduced from the simultaneous MODIS land cover product and a few general ancillary data bases with coarse resolution such as geographic, soil and vegetation type maps; b) the ability of a given model to fit the observed data; a and c) tupixel’s history of bidirectional reflectance. The consistency of pixel interpretation over time will enhance reliability of the inferred surface parameters, and consistency in a change detected will indicate natural and unnatural alterations of the Earth’s surface.

This project uses models such as a modified Walthall model, the extended Roujean-Ross-Li kernel-driven semi-empirical models, a reflectance model for topographic relief, and, where possible, a Li-Strahler geometric optical mutual shadowing model for dense and sparse forest canopies or a Liang-Strahler four-stream radiative transfer model for horizontally homogeneous plant layers. It is planned to provide the EOS-MODIS BRDF/Albedo product to users every 9 days.

(Abstract from the 1994 AGU fall meeting, paper by W. Wanner, A.H. Strahler, X. Li, J.-P. Muller, P. Lewis, M. Barnsley, and C.L. Barker Schaaf)

For further information on NASA’s “Mission to Planet Earth”, refer to:

For some nice images acquired by the MODIS Airborne Simulator, and airborne instrument with MODIS-like characteristics, refer to: