The Global Rain Forest Mapping Project JERS-1 radar mosaic of tropical Africa: Development and product characterization aspects

The Global Rain Forest Mapping Project (GRFM) is an international collabora tive effort initiated and managed by the National Space Development Agency of Japan (NASDA), The main goal of the project is to produce a high resolut ion wall-to-wall map of the entire tropical rain forest domain in four cont inents using the L-band SAR onboard the JERS-1 spacecraft. The processing p hase, which entails the generation of wide area radar mosaics from the raw SAR data, was split according to the geographic area, In this paper, the fo cus is on the part related to Africa. The GRFM project's goal calls for the coverage of a continental scale area of several million km(2) using a sens or with the resolution of tens of meters. In the case of the African contin ent, this entails the assemblage of some 3900 high resolution SAR scenes in to a bitemporal mosaic at 100 m pixel spacing and with known geometric accu racy. While this fact opens up an entire new perspective for vegetation map ping in the tropics, it presents a number of technical challenges, In this paper, we report on the solutions adopted in the GRFM Africa mosaic develop ment and discuss some quantitative and qualitative aspects related to the c haracterization and validation of the GRFM products. In particular, the mos aic geolocation and its validation are discussed in detail. Indeed, the int ernal geometric consistency (subpixel accuracy in the coregistration of the two dates), and the absolute geolocation (residual mean squared error of 2 40 m with respect to ground control points) are key features of the GRFM Af rica mosaic. Other important aspects that are discussed are the multiresolu tion decomposition approach, which allows for tracking the evolution of nat ural phenomena with scale; the internal semi-automatic radiometric calibrat ion, which minimizes artifacts in the mosaic; and the thematic information content for vegetation mapping, which is illustrated by a few examples elab orated by visual interpretation, Experience gained so far indicates that th e GRFM products constitute an important source of information for global en vironmental studies.