Spot 5 Hrs Location Performance Tuning and Monitoring Principles

HRS instrument on board of SPOT5 allows acquisition of stereoscopic pairs in a single pass. This instrument has been subject of specific attention even after the end of SPOT5 in flight commissioning phase. The stake was not only to fulfil HRS' location specification of 50 meters in root mean square but to obtain a location performance as best as possible and at least about 25 meters in root mean square as expected before launch. Moreover, it should be checked that the instrument could cope with the realisation of Reference3D world-wide Digital Terrain Model database, in particular for horizontal accuracy, set to 16 meters for 90% of the points without ground control points. The article gives an outcome of the work carried out to improve the location performance. First, an overview of HRS will be given, with a specific attention paid to the geometric model available through ancillary data given with the images which is the only data available to reach the location performance. Then, methods and means used to reach the objectives will be described : French Space Agency (CNES) and French Mapping Agency (IGN) worked in co-operation to carry on specific analyses at three levels of interpretation. Improvements brought to the performance after the end of the image quality commissioning phase will be detailed : most error sources have been identified and some of them reduced or removed thanks to satellite on board modification or ground models. Finally, a view of the current location performance and a list of error sources will be detailed as a balance of the location performance's level reached. The conclusion will remind of monitoring principles adopted and detail further work planned.