A new collocation system at CERSAT

Since 1994 CERSAT has been archiving, processing and distributing the ERS scatterometer data to users world-wide. In 1996, CERSAT started providing similar services for the NSCAT scatterometer, launched on board the Japanese satellite ADEOS 1 in August 1996. The main problem was to inter-calibrate both instruments to be able to combine these two datasets. Thus in 1996, we decided to generate products collocated between NSCAT, the ERS-2 scatterometer as well as the altimeter to facilitate their calibration/validation tasks. We put these data on our WWW server for scientists who regularly use our datasets. But, the system was designed to generate a specific dataset for each collocation. It was difficult to add a new sensor at short notice. When the QuikScat mission was decided by NASA in 1997, the QuikScat scientific team asked CERSAT to provide collocated datasets between QuikScat and the ERS-2 scatterometer and altimeter and also TOPEX or SSM/I if possible. As collocated datasets seemed to be essential to satellite-driven data applications we decided to build a new system which could “easily” collocate any nuplets (up to 5 in fact) since they were handled by the CERSAT databases. We identified two types of applications using collocated products : calibration/validation applications, geophysical applications. These are discussed