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Madhumathi D.S.

Bangalore, April 5 At a time when the country grapples with terror threats and security concerns have peaked, a radar imaging satellite that is due to be put in orbit later in April is expected to give extra teeth to the nation’s eyes and ears in the sky — ISRO’s constellation of earth observation satellites.

ISRO also plans to send up a second one, Radar Imaging Satellite-2, towards the end of this year to complement the upcoming RISAT-1.

At a time when the Ministry for Home Affairs has put even the space agency’s scientists on terror alert, the project is sensitive to a normally open ISRO, which is playing down the project and its Israeli input. “RISAT-1 (Radar Imaging Satellite) is an all-weather satellite, capable of seeing through rain and cloud; and at night too,” is all its officials would say. It will orbit pole to pole from a height of around 600 km.

The brain of the 1,780-kg RISAT-1 is a C-band synthetic aperture radar (SAR) based on active phased array technology. ISRO has procured the SAR for RISAT-1 from Israel. “Except for the SAR that we procured, it is our satellite,” an official unwilling to be named said, meaning to distinguish it from the TecSAR/Polaris surveillance satellite that the space agency launched for Israel in January 2008.

“Corresponding developments on the ground data processing systems with large computational requirements is yet another requirement,” ISRO’s Web site says.

However, RISAT-2 will be fully indigenous and development work is in progress at the Space Applications Centre, the official said. The US, Europe, Canada and Israel are among the few countries that have the SAR capability. The recent lunar mission — Chandrayaan-1 — uses NASA’s mini-SAR as a guest instrument.

Who will be the primary user of RISAT? How useful will it be to secure vital scientific and commercial establishments that face risk? Will data from RISAT be commercially available, just as data from IRS are? Answers to these will have to wait for now.

A SAR system ‘sees’ opaque objects that take cover under darkness, foliage, haze or clouds. These features, ISRO officials admit, are warranted by India’s risk-ridden location; they were lacking in the IRS remote sensing satellites that have been launched in the last two decades. “Ninety five per cent of our data requirement can be met by (the regular) optical imaging satellites. When we needed radar images, we have obtained them from other satellites like Canada’s Radarsat,” one official said.

A RISAT brings other advantages, such as timely information during floods, natural calamities and quicker assessment of damage and deployment of relief to those areas. A radar imaging spacecraft is estimated to cost much more than the Rs 150 crore that a regular IRS costs.

About RISAT, the ISRO Web site says the radar provides target parameters such as roughness and geometry and has the unique capability for day-night imaging, in fog, haze or any weather conditions. It can glean soil moisture data and give spatial resolutions of 3 metres to 50 metres and a sweep of 10-240 km.

According to information available online, regular earth observation satellites sense reflected sunlight; a SAR transmits microwave energy towards the surface and records the reflections. It can also offer fairly clear terrain features, identify selected man-made targets and movements and can be handy for 24x7 military requirements.

Some SAR systems are built to ‘see’ select underground utility lines, arms caches, bunkers, mines, oil slicks and moving vehicles, says the Web site of US SAR leader Sandia National Laboratories.

More Stories on : Science & Technology | Karnataka

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