Meteorological Satellites Payloads

Currently several operational meteorological satellites are providing global and regional observations. Six different types of satellite systems currently in use are : 1) Visible/ Infrared/Water Vapour Imagers, 2) Infrared Sounders, 3) Microwave Imagers, 4) Microwave Sounders, 5) Scatterometers and 6) Radar Altimeters. Though the water vapour imaging capability is available only on the geostationary satellite, the visible and infrared imagers are available on geostationary as well as polar orbiting satellites. The last four are currently available only on polar orbiting systems. We first describe in detail below the INSAT system which is the primary satellite for weather surveillance in this part of the globe. It is a multipurpose geostationary satellite that caters to the requirements of Meteorology and Communication. It carries a met payload called Very High Resolution Radiometer (VHRR) that enables us to have visible, infrared and now even water vapour images. It is designed to provide the following services:

• Round the clock surveillance of weather systems including severe weather events around the Indian region.

• Operational parameters for weather forecasting - cloud cover, cloud top temperature, sea surface temperature, snow cover, cloud motion vector, outgoing long wave radiation etc.

• Collection and transmission of meteorological, hydrological and oceanographic data from remote/inaccessible areas through Data Collection Platforms.

• Timely dissemination of warning of impending disasters such as cyclones through Cyclone Warning Dissemination Systems.

• Dissemination of Meteorological information including processed images of weather systems through Meteorological Data dissemination system.

INSAT applications programme started with the launch of INSAT-1 series of satellites in early 1980s. INSAT-2 series that followed was designed based on user feedback. INSAT-2A and 2B launched in 1992 and 1993 carried VHRR payload with improved resolution of 2 km in visible and 8 km in thermal band. The imaging capability included three modes, viz. full frame, normal mode and sector mode of 5 minutes for rapid coverage of severe weather systems.

INSAT-2E launched in 1999 carried an advanced VHRR payload operating in three channels - visible (2 km), thermal and water vapour (8 km). The water vapour channel is capable of giving water vapour distribution and flow patterns in the middle troposphere. Besides this, INSAT-2E also carried a CCD camera with 3 channels - visible, near infrared and short wave infrared with 1 km resolution to map the vegetation cover.

A geostationary meteorological satellite (METSAT) system devoted totally to meteorology was launched in 2002. It has been renamed as Kalpana-1 and is currently the operational satellite system being used by IMD.

INSAT-3A has been launched in April 2003 and carries identical payloads as in INSAT-2E. INSAT- 3D planned for future will also carry atmospheric sounder for temperature and water vapour profiles and split thermal channels for accurate sea surface temperature retrieval. Data from INSAT satellites are being used to retrieve a number of quantitative products. INSAT imagery is being used very exhaustively to provide support for synoptic analysis and weather forecasting. The quantitative products available from INSAT and its applications are described in subsequent sections.

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