An Operational Forest Mapping Tool Using Spaceborne Sar Data

SAR data has been shown to offer useful information for forestry applications, and especially in cases of major forest change such as that caused by severe storms or fires. In these situations, the possibility of exploiting radar remotely sensed data which is not affected by phenomena such as water vapour, smoke or clouds provides great advantages with respect to optical sensors. Under these circumstances, the availability of operational tools dedicated to forest monitoring is of great interest. This paper presents the main achievements of a project that was carried out in the framework of ESA's Data User Programme (DUP), and which was dedicated to the development of an operational software tool for mapping of forests and forest damage using SAR data as the primary input. The modular SAR processing chain, is embedded in the ArcView GIS environment. In this way, within the processing chain, SAR data can be merged with other remote sensing and/or auxiliary data, in vector or raster format (e.g. ATSR hot spot products for fire detection). Such modularity allows the system to be used in a very flexible way and the processing flow can be decided by the user in order to combine various data products for extracting different information. The performance of this system, and the resulting thematic products are shown for a number of sites, where different events have been mapped and monitored. One example of hurricane damage mapping is shown over the Swiss/French Jura region. Examples of forest and burn scar mapping and their evolution in time are discussed for sites in both Canada and Madagascar. INTRODUCTION The utility of spaceborne radar data for forest applications is now well known. Yet, the use of SAR data as an integral part of operational forest mapping and monitoring systems is still very limited. There is a common perception that SAR data is more difficult to use and interpret than data acquired using optical systems. Although now, most popular remote sensing packages include some radar processing modules the functionality is rather limited and incomplete. ESA have recognised the lack of systems conceived primarily for handling SAR data and have therefore introduced the ERS SAR Toolbox Software [1], which performs speckle filtering, radiometric calibration and simple statistical analysis for a range of ERS SAR products. In order to provide a more complete system, developed specifically with the SAR user in mind, we have developed an end to end SAR image processing system embedded in ArcView, which allows even an inexperienced SAR user to do multilook and interferometric processing, speckle filtering, radiometric correction, geocoding and classification of SAR data from a number of sensors. Advanced users are also catered for by building in the possibility to change key parameters in the processing chain. This commercial software which is loaded as an extension in ArcView is called SARscape. The use of SARscape is illustrated for three studies; one on the Lothar storm which caused serious damage across central Europe at the end of 1999 and the other two on an ESA Data User Programme (DUP) project dedicated to forest and burnt area mapping in different parts of the globe. Large areas of forested land were damaged and destroyed by the Lothar storm which crossed France and central Europe on the 26 and 27 of December 1999. The Swiss federal institute with responsibility for forest (WSL) required to know the extent and boundaries of the areas damaged in order to design a cleaning and rehabilitation plan for the federal forests. The potential of identifying and mapping the damaged areas was assessed by sarmap using images provided by ESA/ESRIN. One of the key elements of the DUP study was the evaluation of ERS SAR for the mapping of burnt areas in different environments and vegetation types. Test sites were selected in Canada, Madagascar and Italy. Each site is representative of an area which experiences numerous fires each year. In Canada and Alaska up to 3 million Ha of forest burn each year. Although only around 40% of the fires are due to lightning, it is believed that they are responsible for up to 80% of the area burned. The area burned in Siberia is not well known but could very well be many millions of hectares [2]. In addition to the loss of timber resources, boreal fire makes a net contribution of carbon to the atmosphere due to the burning of the soil organic carbon layer [3]. In order to improve estimates of biomass consumed and hence quantities of gases emitted, there is a need for better mapping of the extent and severity of these boreal fires. In the tropics, where currently most fires occur [4], much burning is associated with land use: the clearing of forest and brush land for agricultural use, control of scrub, weeds and litter accumulation on grazing and crop lands, nutrient regeneration in grazing and crop lands and control of fuel accumulation in forests [5]. Madagascar is no exception to this general pattern and experiences widespread fire activity each year. As part of a forest management programme near Morondava, there is a need to monitor the changes in forest extent and the amount of burning. SAR data is of particular interest because of its all weather ability in this frequently cloudy region. This paper describes the functionality of the SARscape system and outlines the processing methodology. Results of forest mapping and burnt area detection, using ERS SAR data processed and analysed with this software tool, are presented.