Recent Improvements in Cloud Motion Vector Derivation from Insat

Cloud Motion Vectors were being derived since 1984 from INSAT, using visible imagery for cloud tracking and infrared temperatures for height assignment. The derivation was made at 0600 UTC daily over the Arabian Sea, Bay of Bengal and a limited area of the western and central Indian Ocean. The method used was basically an automated procedure with a manual quality control. INSAT-2A, the first of India's second generation operational satellites, was launched in July 1992. The INSAT-2A VHRR has an improved resolution of 2 km in the visible channel and 8 km in the infra-red channel. Coinciding with the launch of INSAT-2A, the ground data processing system was also upgraded. This has made it possible to derive CMVs at the standard synoptic hours of 0000 and 1200 UTC using infra-red channel data for cloud tracking as well. The system is capable of deriving up to 1000 wind vectors over the entire Indian Ocean from triplet images within about two hours. The CMV information is disseminated on the GTS. This paper describes in detail the computational procedure currently used for extraction of INSAT CMVs, the techniques adopted for quality assurance, typical situations showing the usefulness of the INSAT CMVs, validation exercises and future plans for further improvements in the algorithms.