Characterising vegetation structure using MODIS multi-angular data

Bidirectional Reflectance Distribution Functions (BRDF) seek to represent variations in surface reflectance resulting from changes in a satellite sensor’s view and solar illumination angles. NASA’s Moderate Resolution Image Spectroradiometer (MODIS) is a wide field of view Earth orbiting sensor that generates observations over a large range of view angles. Based on MODIS observations, a BRDF product and several sub-products have been developed by MODIS science teams, i.e. the MCD43 product suite. With the aim of using BRDF information from the MCD43 product to assist with the characterisation of the vertical structure of vegetation, a simple geometric optical model has been developed within this thesis for interpreting the MCD43 BRDF product in terms of an alternative set of parameters. The model developed within the thesis, and its application to single species cropped fields, a transect between Melbourne – Darwin and a semi-arid area in central Australia. The thesis identified that reflectance variations associated with enlargement of pixels’ ground instantaneous field of view is the principal source of variation in the MODIS BRDF product; rather than directional scatter effects that the product is intended to measure. Variations in pixels’ ground instantaneous field of view is a well known effect associated with wide field of view sensors such as MODIS, but is not explicitly considered in the MODIS BRDF algorithm. The presence of this artefact within the MODIS BRDF product has implications for the validity, use and interpretation of all land surface products based directly or indirectly on MODIS BRDF modelling.