Precise geometric registration of ASAS airborne data for land surface BRDF studies

Considers the special problems that must be addressed when registering multi-angle images acquired by airborne multispectral scanners, such as NASA´s Advanced Solid-state Array Spectroradiometer (ASAS). The limitations of standard registration procedures are discussed, and an alternative approach making use of automated control-point selection and image correlation are outlined. The application of this approach is illustrated using eight look angles, ranging from 60° forward to 30° backward, from one flight line acquired by ASAS over the HAPEX-Sahel test site in Niger, for which an average RMS residual error of 0.36 pixels across is demonstrated. Finally, some observations are made regarding the registration and resampling of multi-angle and multi-scale data. These are discussed in light of plans to use multi-angle satellite data acquired by future satellite sensors to estimate various biophysical properties of the land surface, and to detect changes in these properties over time