Earth observation satellites can be defined as “satellites specifically designed to observe Earth from orbit, similar to spy satellites but intended for non-military uses such as environmental monitoring, meteorology and map-making. Most Earth observation satellites carry instruments that should be operated at a relatively low altitude. Altitudes below 500-600 kilometers are generally avoided, though, because of the significant air drag at such low altitudes making frequent orbit raising maneuvers necessary.”
A weather satellite can be defined as “a satellite primarily used to monitor the weather and climate of the Earth. These meteorological satellites see more than cloud and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows etc are other types of environmental information collected using weather satellites”
RISAT-1 (Radar Imaging Satellite-1), the result of more than10 years of research by ISRO (Indian Space Research Organization) finally became a reality when the 1858 kg satellite, “the country’s first microwave remote sensing satellite” was launched successfully in its desired orbit by a Polar Satellite Launch Vehicle (PSLV C-19) from ISRO’s Satish Dhawan Space Centre about 90 kilometers from Chennai. The speciality of RISAT-1 is that instead of relying on optical and infrared sensors like it’s previous prototypes, it uses a special “C band Synthetic Aperture Radar” (SAR) which has the capability of penetrating through clouds and darkness and send images thus ensuring an all weather Earth monitoring and observation. The main features of RISAT-1 include:
• 160 X 4 Mbps Data handling system.
• 50 Newton-meter second reaction wheels
• SAR antenna deployment mechanism
• Phased array antenna with dual polarization
(Source of satellite features- Internet)
One of the most important features of the satellite is its “active phase array antenna”. The microwave signals, instead of being generated by a single device, this particular antenna has a considerable number of “modules”, which together generate the radar beam in unison. The unique feature of this kind of a radar beam is that it can be electronically moved around like the focus of a searchlight. Due to the large number of modules, failure of a few modules will delimit the satellite’s function only to a negligible extent. The satellite has been designed to transmit coarse, fine and high resolution images even in darkness or other adverse weather conditions thus serving multiple applications.
The successful launch of the Rs378 crore satellite RISAT-1 is another milestone in Indian space technology and has secured India a permanent position in the elite league of US, Canada and European countries who only had the radar imaging technology in the whole world so far. In fact RISAT-1 is expected to outperform the currently operational Canadian second generation RADARSAT-2 in many aspects. The RISAT-1 images will be helpful in multiple fields. Other than being an all weather Earth observation satellite, the images transmitted will not only help in agriculture like crop forecasting and disaster management but will also serve strategic needs. The RISAT-1 will prove to be an indispensable source of intelligence for the military, providing important surveillance data about the Indian border conditions and forewarning about adverse situations so a repeat of the Kargil skirmish can be avoided. The new “smart eye in the sky” will definitely be an effective fallback system for the Indian Military who currently has very limited access to satellite imagery. So far the Cartosat series of satellites of ISRO had been the chief source of intelligence for the military in various strategic activities like terrain mapping and in depth understanding of landscapes but with the addition of RISAT-1, the Indian Military is definitely going to have an extra edge.
“India currently has 11 remote sensing and earth observation satellites in orbit providing imagery at different resolution levels, from 500meters to about one meter resolution. These spacecrafts include the TES, Resourcesat-1, Cartosat-1, 2, 2A and 2B, IMS-1, Oceansat-2, Resourcesat-2 and Megha Tropiques”. However, the RISAT-1 is the only indigenous satellite with radar imaging technology, a promise from ISRO of further breakthroughs in Indian Space Technology.
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