Synergetic use of multi-temporal ALOS PALSAR and ENVISAT ASAR data for topographic/land cover mapping and monitoring at national scale in Africa

The use of Synthetic Aperture Radar (SAR) data in large parts of the African countries, in particular for those close to the equator, is often conditio sine qua non, simply due to the fact that optical data are severely hampered by clouds, especially during the raining (corresponding to the crop) season. The objective of this paper is to present a methodology - and the related results - for the generation of land cover maps and changes over large areas by fusing single-date or interferometric ALOS PALSAR Fine/Dual Beam data with multi-temporal ENVISAT ASAR Image Mode/Alternating Polarization intensity. In synthesis, the method is based on data fusion by exclusively considering - in the prior knowledge-based classifier that requires neither user-defined parameters nor reference samples - the data characteristics and related acquisition modes. Results clearly show that the synergetic use enables the reliable identification of key land cover types (in particular cropped areas, bare soil areas, forestry, forest clear cut, forest burnt areas, water bodies) and their evolution over time, providing basic information on the land cover status. Finally, it is shown that using the same 46-days interferometric ALOS PALSAR data set, a Digital Elevation Model (DEM) with higher quality than the Shuttle Radar Topographic Mission (SRTM) one can be generated in those nearly equatorial - non dense forest - regions.