K&C Africa Palsar Mosaic: Geocoding and Calibration Issues in Prototype Development
Gianfranco De Grandi(1), Jan Kropacek(1), Masanobu Shimada(2), Francesco Holecz(3), Paolo Pasquali(3), Ake Rosenqvist(1) and Desiree Johansson(1)
(1) DG Joint Research Center, via Fermi - TP 440, 21027 Ispra (VA), Italy
(2) JAXA/EORC,, Sengen 2-1-1, 305-8505 Tsukuba, Ibaraki, Japan
(3) SARMAP s.a., Cascine di Barico, 6989 Purasca, Switzerland
In the framework of the JAXA K&C project, a mosaic of PALSAR dual-polarization observations over the whole African continent is under development at the Joint Research Center (JRC). The mosaic compilation is based on hundreds of strip slant range detected images at 50 m resolution provided by JAXA using the SIGMASAR processor. This paper reports on a number of issues that had to be addressed during the design and implementation of the mosaic processing chain, and the prototype development. The mosaic processing chain is mainly based on the commercially available SARSCAPE software by SARMAP s.a., with the addition of bespoke modules written in IDL. The following points are discussed. Generation of a digital elevation model with suitable accuracy and coverage. The solution calls for the use of 10 tiles (30x30 degrees) of USGS supplied SRTM (version 3), and suitable interpolation of missing data. Modification of the geocoding range-Doppler algorithm to take into account the squinted geometry of the JAXA strip data sets. Verification of the geometric accuracy and geometric fidelity in high topography areas. Radiometric revision for correcting dependences of backscatter on incidence angle. Mosaicking algorithms including a global minimization of radiometric discrepancies in overlapping areas.
The quality of the resulting products and the richness in thematic content is demonstrated by a gallery of detailed imagery at full resolution and focusing on different land cover types of the African continent.