The RISAT series are the first all-weather earth observation satellites from ISRO. Previous Indian observation satellites relied primarily on optical and spectral sensors which were hampered by cloud cover.
After the November 26, 2008 Mumbai attacks, the launch plan was modified to launch RISAT-2 before RISAT-1, since the indigenous C-band SAR to be used for RISAT-1 was not ready. RISAT-2 used an Israel Aerospace Industries (IAI) X-band SAR sensor similar to the one employed on TecSAR.
 RISAT 2
RISAT-2 was the first of the RISAT series to reach orbit. It was launched successfully on April 20, 2009 at 0015 hours GMT by a PSLV rocket. The 300-kg satellite was built by ISRO using a X-band SAR manufactured by IAI.
This satellite was fast tracked in the aftermath of the 2008 Mumbai attacks. The satellite will be used for border surveillance, to deter insurgent infiltration and for anti-terrorist operations. It is likely to be placed under the Aerospace Command of the Indian Air Force.
No details of the technical specifications of RISAT-2 have been published. However, it is likely to have a spatial resolution of about a metre or so. Ship detection algorithms for radar satellites of this class are well-known and available. The satellite also has applications in the area of disaster management and agriculture-related activities.
 RISAT 1
RISAT-1 is an indigenously developed radar imaging satellite successfully launched by a PSLV-C19 rocket on April 26, 2012 from Satish Dhawan Space Centre, Shri Harikota. RISAT-1 was postponed in order to prioritize the building and launch of RISAT-2.
The features of RISAT-1 include:
- 160 x 4 Mbit/s data handling system
- 50 Newton-meter-second reaction wheels
- SAR antenna deployment mechanism
- Phased array antenna with dual polarisation
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- Launch Info
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