Contribution of radar imagery to tropical forest monitoring and management

A general state-of-the-art assessment is presented of the possible usefulness of radar images for tropical forest inventory and monitoring, using examples from Indonesia. This decade has seen the launch of new spaceborne sensors using synthetic aperture radar (SAR) technology: ERS- I and ERS-2 (European Space Agency), J-ERS (NASDA, Japan) and Radarsat (Canadian Space Agency). These tools offer new opportunities to monitor land surfaces and particularly tropical forests, although it has not yet been used operationally for applications at local and regional scales. In addition to their all-weather capabilities, ensuring repetitive acquisition day or night, microwaves used by SAR can probe vegetation covers and are sensitive to some extent to cover structure, biomass and water status. In addition, multi-temporal use of SAR images allows monitoring of environmental and man-made changes such as clear-cutting of primary forest or burnt areas such as were the result of the large Indonesian fires that occurred in 1997. However, this technology is relatively new and the information content relative to tropical forest characteristics and their dynamics still need to be understood for the development of robust applications useful for tropical forest management. In addition, significant limitations, specific to SAR images, exist for which recent research results can hopefully provide operational solutions with in-house or commercial image processing software: availability of I channel for a given sensor speckle noise and image distortions in hilly terrain situations. This paper discusses the main areas where SAR images can play a role in the monitoring of tropical forests: land cover and forest type mapping; forest monitoring and mapping of clear-cutting; and the construction of Digital Elevation Models. (Résumé d'auteur