The ERS-1 Central Africa Mosaic: A new perspective in radar remote sensing for the global monitoring of vegetation

The Central Africa Mosaic Project (CAMP) is an attempt to bring spaceborne synthetic aperture radar (SAR) remote sensing into an entirely new perspective for tropical forest monitoring. This goal represents a drastic change in the use of radar data, as it brings high-resolution SAR from the role of gap-filler and local hot spot analysis to the role of global mapping at a semicontinental scale. CAMP consists of more than 400 ERS-1 SAR scenes, which were acquired on demand and in a short time frame (two months) over the entire Central Africa region by the ESA Libreville ground station and correlated by the German Processing and Archiving Faculty (PAF) at DLR, The work was carried out in the monitoring of the tropical vegetation unit (MTV) of the European Commission Space Applications Institute (SAI), Ispra, Italy, and within the R/D activity of the Tropical Ecosystem Environment Monitoring by Satellites (TREES) project. This paper will give an overview of the CAMP project. The general setting is first established through the motivation and the rationale, as seen in the context of the TREES objectives. The main underlying concepts and the major innovative aspects of the CAMP machine, such as multiresolution pyramidal information structure and processing on demand, are highlighted. The focus is then shifted onto some radar science aspects and engineering issues of the processing chain, such as the statistical characterization of the baseline low-resolution products, and radiometry-related problems. Preliminary thematic results based on visual interpretation are finally reported. At this stage of the project, it can already be concluded that the material provided by the ERS-1 Central Africa Mosaic constitutes a unique source of data on vegetation distribution at a continental scale. The most celebrated "all-weather" characteristic of active microwave sensing has taken its full meaning in the present case since a whole equatorial region has been covered on demand and in a minimum amount of time, and since a significant level of information on forest conditions has rapidly been extracted. This places the ERS-1 SAR approach firmly in a central position in the set of instruments to be further exploited for tropical forest monitoring.