Eye in the sky

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Eye in the sky

RISAT-2B will enhance India’s monitoring capabilities for civil and military purposes

Source: https://www.thehindu.com/opinion/editorial/eye-in-the-sky/article27210902.ece

Why in news?

  • The RISAT-2B satellite, launched by the Indian Space Research Organisation (ISRO) on May 22, adds to India’s capability to observe the earth in all weathers and all conditions.

The launch

  • The Indian Space Research Organisation (ISRO) used its Polar Satellite Launch Vehicle to launch the 615-kg RISAT-2B satellite, capable of clear viewing during the day, night and even under adverse weather conditions, at 5:30 am on May 22.
  • Low earth orbit: The special radar-enabled satellite has been placed at a low earth 557-kilometre orbit, a suitable level for detecting hostile installations as well as monitoring agriculture, forestry and possible disaster zones. The space agency did not release details or photographs of the satellite, considering that it is meant for strategic needs.
  • Balakot air strike: The Indian Air Force (IAF) had sent Mirage 2000 fighter jets to strike a terror camp in Balakot, deep inside Pakistan territory, on the morning of February 26.
    • Some experts have speculated that heavy cloud cover at the time could have blinded Indian satellites, resulting in no images or videos of the operation being released so far.
    • Now, with a new set of radar-enabled satellites at its disposal, the space agency hopes to provide India’s armed forces with the ability to keep track of activities across its eastern and western borders.
  • Existing satellites: Although the country also has high-resolution optical imaging CartoSAT satellites, they get blinded by dense cloud cover. Moreover, their imaging resolution was possibly not good enough to make an accurate damage assessment after the IAF strike in Balakot.
  • RISAT 1 & 2: Two previous radar-enabled satellites launched by India into space were RISAT-1 and RISAT-2, the latter being an acquisition from Israel.
    • RISAT-1: The RISAT-1, a C-band radar imaging satellite, was not available for recording the impact of the Balakot strikes because it was declared dead in 2017.
    • RISAT-2: However, there is no clarity on why images from the RISAT-2, a tiny 300 kg satellite with an X-band radar launched in the wake of the 2008 Mumbai attacks – have not been released.


  • With the successful pre-dawn launch of RISAT-2B satellite on May 22, the Indian Space Research Organisation (ISRO) has added another feather to its cap.
  • Radar images: The RISAT, or radar imaging satellite, is equipped with a sensor known as ‘synthetic aperture radar’ that takes what are known as ‘radar images’.
    • much like the flashlights of the camera, which release visible light to illuminate an object and then use the reflected light to create an image,
    • the synthetic aperture radar send out hundreds of radio signals every second towards the subject (in this case, the earth) and capture the reflected signals to create a radio image, which can then be used by computers to build a real image.
  • Application: ISRO said the images taken by RISAT-2B would be used for applications in agriculture, forestry and disaster management support.
    • But services of such satellites are also in great demand from national security agencies as well.

All-season satellite

  • The satellite will enhance India’s capability in crop monitoring during the monsoon season, forestry mapping for forest fires and deforestation, and flood mapping as part of the national disaster management programme.
  • All-weather satellite: When it is cloudy or dark, ‘regular’ remote-sensing or optical imaging satellites — which work like a light-dependent camera — cannot perceive hidden or surreptitious objects on the ground.
    • Satellites that are equipped with an active sensor, the synthetic aperture radar (SAR), can sense or ‘observe’ Earth in a special way from space day and night, rain or cloud.
    • Because the very large wavelength radio waves are not obstructed by clouds, dust or similar other obstacles in the atmosphere, they produce reliable images during day and night and all seasons.
    • This all-weather seeing feature is what makes them special for security forces and disaster relief agencies.
    • Given that overcast skies are a constant during the monsoon season and during times of flood, the ability to penetrate the cloud cover is essential.
    • While optical remote sensing that relies on visible light for imaging gets obstructed by clouds, RISAT-2B will not.
  • Microwave radiation: Much like the RISAT-1 satellite that was launched by ISRO in April 2012, RISAT-2B will also use microwave radiation.
    • Unlike visible light, microwaves have longer wavelength and so will not be susceptible to atmospheric scattering.
    • Microwave radiation can thus easily pass through the cloud cover, haze and dust, and image the ground. Hence, RISAT-2B satellite will be able to image under almost all weather and environmental conditions.
    • Since it does not rely on visible light for imaging, it will be able to image the ground during both day and night.
    • The satellite does not have passive microwave sensors that detect the radiation naturally emitted by the atmosphere or reflected by objects on the ground.
    • Instead, RISAT-2B will be transmitting hundreds of microwave pulses each second towards the ground and receiving the signals reflected by the objects using radar.
    • The moisture and texture of the object will determine the strength of the microwave signal that gets reflected.
    • While the strength of the reflected signal will help determine different targets, the time between the transmitted and reflected signals will help determine the distance to the object.
  • X-band synthetic aperture radar: The RISAT-2B satellite uses X-band synthetic aperture radar for the first time; the synthetic aperture radar was developed indigenously.
    • Unlike the C-band that was used by RISAT-1, the shorter wavelength of the X-band allows for higher resolution imagery for target identification and discrimination.
    • Since it has high resolution, the satellite will be able to detect objects with dimensions of as little as a metre. This capacity to study small objects and also movement could be useful for surveillance.

Way ahead

  • As K. Sivan, ISRO Chairman and Secretary, Department of Space, had said in April, the satellite could be used for civil and strategic purposes.
  • RISAT-2B will have an inclined orbit of 37 degrees, which will allow more frequent observations over the Indian subcontinent.
  • With ISRO planning to launch four more such radar imaging satellites in a year, its ability to monitor crops and floods as well as engage in military surveillance will be greatly enhanced.

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