The RISAT-2B satellite was launched with the PSLV-C46 by the Indian Space Research Organisation (ISRO).
What is the RISAT?
Two satellites in RISAT (radar imaging satellite) series have earlier been launched by ISRO.
RISAT-2 was the first one to be launched, in 2009, while RISAT-1, which had got delayed, was launched only in 2012.
RISAT-1 is no longer operational.
After a very long time, ISRO’s PSLV rocket was used to launch just one satellite into space.
In recent times, ISRO has been launching multiple satellites at one go.
What are the key features?
The RISAT, or radar imaging satellite, is equipped with a sensor known as ‘synthetic aperture radar’, to take "radar images".
It works much like the flashlights of a camera, which release visible light to illuminate an object and then use the reflected light to create an image.
The synthetic aperture radar transmits hundreds of radio signals (microwave pulses) every second towards the ground.
It then captures the signals reflected back by the objects, to create a radio image, which can then be used by computers to build a real image.
The moisture and texture of the object will determine the strength of the microwave signal that gets reflected.
The strength of the reflected signal will help determine different targets.
Likewise, the time between the transmitted and reflected signals will help determine the distance to the object.
Unlike visible light, microwaves have longer wavelength and so will not be susceptible to atmospheric scattering.
In other words, the very large wavelength radio waves are not obstructed by clouds, dust or other such obstacles in the atmosphere.
So they produce reliable images during day and night and all seasons.
The RISAT-2B satellite uses X-band synthetic aperture radar for the first time, which was developed indigenously.
Unlike the C-band that was used by RISAT-1, the X-band allows for higher resolution imagery for target identification and discrimination.
[C-band and X-band are the designations for a band of frequencies in the microwave radio region of the electromagnetic spectrum.]
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.
What is the significance?
RISAT-2B adds to India’s capability to observe the earth in all weathers and all conditions.
It will enhance India’s monitoring capabilities for civil and military purposes, which include -
crop monitoring during the monsoon season
forestry mapping for forest fires and deforestation
flood mapping as part of the national disaster management programme
Given that overcast skies are a constant during monsoon season and 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.
Services of such satellites are in great demand from national security agencies as well.
