Special Issue on RISAT-1, Current Science, 25 March 2013 - Space ...

Radar Imaging Satellite-1With the launch of Radar ImagingSatellite-1 (RISAT-1), a new chapterhas been opened in Indian SpaceResearch Organisation’s (ISRO), EarthObservation (EO) programme – indigenouscapability of developing,launching and operation of microwaveimaging sensor. A set of fivearticles, in this special issue, tracesall aspects of RISAT-1 from developingthe SAR sensor to illustratingdifferent possibilities of utilizing itsdata in day to day practical applications.In the Foreword, A. S. Kirankumar(page 444), one of the primearchitects of ISRO’s EO programme,enunciates the significance of RISAT-1from the overall perspective ofISRO’s EO mission, especially howit complements existing array of sensorsin optical bands and its additionalstrengths which are unique tomicrowave bands and its ability tomeasure all the components of electromagneticwaves, i.e. polarization,amplitude and phase.RISAT-1 Synthetic Aperture Radar(SAR) payload is a complex payloadwith a very large array of imagingcapabilities in-built. It is not onlyISRO’s first SAR payload in space,but also India’s first state-of-the-artactive antenna in space. Further, forthe first time, it is carrying the capabilityof all traditional SAR imagingmodes in optional hybrid polarimetryconfiguration. Design philosophybehind RISAT-1 SAR, its realization,illustration of initial results and itscalibration have been brought out inthe article by Tapan Misra et al.(page 446).In this issueRISAT-1 SAR is the heaviest payloadbuilt in ISRO, weighing close to950 kg. The challenge was to accommodateit in a satellite bus which canbe flown in PSLV. The large SARantenna provides obstruction to viewinggeometry of satellite sensors anddata transmission systems. Further,designers wanted a simplified antennadeployment system which guaranteessuccess. Moreover, spacecraft resourceshave to cater to large powerdemand (~5 kW) and high data rate(~1.5 Gbps) for SAR operation. Allthese requirements resulted into anew and unique bus configuration,distinct from ISRO’s traditionalworkhorses like IRS and INSAT.The complete gamut of RISAT-1 satelliteconfiguration is presented byN. Valarmathi et al. (page 462).RISAT-1 is also the heaviest satellite(dry mass wise) built in ISRO,bordering on the outer limit of thelaunch capability of highest versionof PSLV. Specific PSLV XLlauncher configuration and its resultantperformances, very close to theintended ones, are presented in thearticle by P. Kunhikrishnan et al.(page 472).RISAT-1 has a very large numberof flexible imaging capabilites, operatedtransparently by on-board computer.For its seamless operation,complex mission planning and operationwere built in ground control ofspacecraft from ISTRAC, Bangalore.Further, ISRO’s data reception systemat NRSC, Hyderabad had to beupgraded by six folds from 110 to640 Mbps for RISAT-1 operation.The data processing, archiving anddissemination system for RISAT-1had to be integrated in new IMGEOSfacility of NRSC. The heart of theground segment is a complex SARsignal processor, implemented inboth off line and near real time processingsystems at NRSC, to convertnoise like SAR signals to meaningfuldigital images with all the correctionsand map projections for disseminationto users in user friendlyand universally acceptable data formats.All the facets of Ground Segment,as these activities are referredto in ISRO parlance, are presented inthe article by V. Mahadevan et al.(page 477).Ultimate aim of RISAT-1 programmeis to convert digital imagesto meaningful, user-specific geophysical,ecological and myriad otherapplication information so thatstrength of RISAT-1 data is harnessedby governmental agencies,commercial entities, global users, resourcescientists and general public.During the course of spacecraft’slifetime and beyond, there is a possibilityof getting the data used formany different applications, limitedby basic physics behind the radarsignal, its interaction with earth elementsand ingenuity of resourcescientists. Very initial results, in thisendeavour, are presented in the articleby Manab Chakraborty et al.(page 490).402CURRENT SCIENCE, VOL. 104, NO. 4, 25 FEBRUARY 2013