Radiometric Block-adjustment of Satellite Images Reference3d® Production Line Improvement

One layer of global geographic database Reference3D® is an image mosaic (5m resolution) made exclusively from panchromatic SPOT5-HRS images. In order to improve Reference3D® production line, in particular SPOT5 HRS images mosaicking step, a new strategy of radiometric block adjustment of satellite images was developed, implemented and tested at French mapping agency IGN. By analogy with “geometric” block adjustment, we developed an iterative algorithm, adapted to Reference3D datasets (many overlapping images covering a wide area), that calculates for each image a polynomial model to apply to its radiometry. These polynomials are found by least-square resolution of a global linear system. Among many tests conducted to try different parameters and validate the process, we present here results of a test case over Algeria (9 not too cloudy images taken in less than 3 months) and another more difficult over Tasmania (11 very cloudy images taken in 4 years). In both cases, radiometric differences between images were dramatically reduced. Reference3D contains also a DEM obtained by merging overlapping DEMs (calculated by automatic image matching of SPOT5-HRS stereo-pairs). Radiometric block adjustment methodology can be easily adapted for DEMs tilting, a preliminary step before merging. So, thanks to these new processes, previously manual tasks in reference3D® production line are now mostly automatic.