RISAT-1. Radar Imaging Satellite

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Radar Imaging Satellite IRS satellites so far have been designed to provide data in the visible and near infrared region of electro-magnetic spectrum. The collection of data in these bands by the electro-optic imaging sensors has a limitation in the presence of clouds and fog, as the electromagnetic radiation in these wavelengths cannot penetrate the clouds/fog. India being a tropical country has a perennial cloud presence during kharif season (July October), which is the prime monsoon period in the country, limiting seriously the visible and near IR data from satellites for any meaningful applications. This season is very important from agricultural production point of view and the country is also prone during this season for disasters such as flood, cyclones and storm surges. Besides, the visible & near IR data can only be obtained during daytime as it depends on sun's reflected radiation for data collection. It is where the use of microwave remote sensing data becomes essential. Microwave data such as Synthetic Aperture radar (SAR) has the innate capability of collecting data in day/night and all weather conditions as it operates in microwave bands for which the atmosphere is transparent. With the known radar backscatter sensitivity to soil moisture and surface roughness, SAR has become an important component in many applications, either in a stand-alone mode or in complementary/ supplementary to electro-optical sensors, and has been extensively used in areas such as agriculture, oceanography, forestry, geology and hydrology. Radar Imaging Satellite (RISAT-1), a new class of remote sensing satellite distinct from the established IRS class, is being developed by Indian Space Research Organisation (ISRO) as its first satellite imaging mission using an active radar sensor system. RISAT-1 carries a multi-mode C-band Synthetic Aperture Radar (SAR) as the sole payload. The RISAT Mission is envisaged to augment the operational remote sensing programme in the country mainly enhancing agriculture and disaster support related applications. RISAT is slated for launch using PSLV by during the second half of 2008.
Mission The primary mission objectives of RISAT-1: • To design, develop, launch and operate a space based SAR mission operating in multi-polarisation, multi-imaging modes with the mission life of atleast 5 years. • To establish ground segment to receive, process and provide SAR data products and services in an operational manner to the user community • To enable integrate with the existing applications and help develop newer applications. RISAT-1 will be launched into a polar sun synchronous orbit of 610 kms with the local time of equatorial crossing at 6.00 AM in descending node, as SAR does not need sun illumination for the target. The choice of this orbit gives advantage in terms of maximizing the power generation, with lesser complexities in solar panel tracking arrangements and power system management, besides simplifying the thermal management. This orbit also meets the basic repetitivity cycle requirement of around 25 days for the medium resolution (25m) mode of SAR. EARTH SENSOR STAR SENSOR SOLAR PANEL THRUSTERS SAR ANTENNA The major orbit parameters Altitude – 610 Km, polar, circular Inclination – 97.844° Local time of pass – 6.00 AM
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RISAT-1. Radar Imaging Satellite

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