The RISAT Radar Satellites Explained

RISAT, short for Radar Imaging Satellite, is the Indian Space Research Organisation’s (ISRO) series of earth-observation satellites that carry synthetic-aperture radar (SAR) to take images of the earth’s surface through clouds, haze and darkness, day and night. Unlike conventional optical satellites that need sunlight and clear skies, the RISAT satellites send out their own microwave signals and record the echoes, which lets them watch India’s land and coasts in all weather.

The RISAT series began with RISAT-2 in 2009 and RISAT-1 in 2012 and has since grown into a family that includes RISAT-2B, RISAT-2BR1, RISAT-2BR2 and RISAT-1A (also known as EOS-04). The satellites support agriculture, forestry, flood and disaster mapping and, as widely reported, military and border surveillance. All have been launched on ISRO’s Polar Satellite Launch Vehicle (PSLV).

Quick Facts

Key Takeaways

• RISAT is ISRO’s series of Radar Imaging Satellites that use synthetic-aperture radar to image the earth through clouds, haze and darkness.
• RISAT-2, launched in April 2009 with an Israeli-origin X-band radar, was brought forward after the 2008 Mumbai attacks to strengthen surveillance.
• RISAT-1, launched in April 2012, was India’s first indigenous C-band radar imaging satellite and was designed mainly for agriculture, forestry and flood mapping.
• The RISAT-2B and RISAT-2BR series, launched on the PSLV from 2019 onward, use X-band radar and are widely reported to serve military and border surveillance as well as civilian needs.
• Synthetic-aperture radar lets RISAT satellites provide data during the monsoon, when cloud cover blocks optical satellites such as the Cartosat and Resourcesat series.
• Every RISAT satellite launched so far has flown on the Polar Satellite Launch Vehicle (PSLV), ISRO’s workhorse rocket.

What is RISAT?

RISAT is a family of Indian radar-imaging earth-observation satellites that use synthetic-aperture radar to map the land and sea surface regardless of light or weather. The name stands for Radar Imaging Satellite, and the series is run by ISRO under the Department of Space.

The aim of the programme was to give India a dependable all-weather imaging capability. Most Indian remote-sensing satellites in the earlier IRS family carry optical or infrared cameras, which cannot see through the thick cloud of the monsoon season, when floods and crop sowing are at their most critical. A radar satellite fills that gap.

The series is not a single design. It includes satellites in two different microwave bands, built by different teams at different times, which is why the names RISAT-1, RISAT-2 and RISAT-2B point to distinct spacecraft rather than successive upgrades of one model.

How does synthetic-aperture radar work?

Synthetic-aperture radar works by sending pulses of microwave energy toward the ground from a moving satellite, recording the returning echoes, and combining many echoes along the flight path to create a sharp image. The word synthetic refers to the fact that the moving satellite acts as though it had a much larger antenna than it physically has.

A real antenna of small size would produce blurry images from space. By processing the signal received at many positions along the orbit, the radar achieves a resolution that would otherwise need an antenna many kilometres long. This is the central idea that makes SAR practical from orbit.

The image formed is different from a photograph. Each pixel represents how strongly the surface reflects the radar signal back. Several things shape this brightness.

• Surface roughness: rough surfaces such as ploughed fields scatter more signal back, while smooth surfaces such as calm water reflect it away and appear dark.
• Moisture: wet soil and vegetation reflect radar differently from dry ground, so soil moisture and crop growth can be inferred.
• Structure: buildings, ships and metal objects often appear as bright points because of corner-like reflections.
• Polarisation: radar can transmit and receive in different orientations of the wave, which reveals extra information about the target.

Because the satellite supplies its own illumination and microwaves pass through clouds, smoke and haze, the images do not depend on sunlight. This is why SAR is described as an all-weather, day-and-night sensor.

Why does India need radar imaging satellites?

India needs radar imaging satellites because large parts of the country are covered in cloud during the monsoon, and many of its most important events, such as floods, cyclones and the main crop season, occur precisely at that time. Optical satellites often fail to see the ground in these conditions.

A second reason is security. India has long land borders, a very long coastline and a large maritime zone to watch. Radar images allow analysts to detect changes on the ground, track ships and observe sensitive areas whatever the weather and at any hour.

A third reason is the national interest in strategic independence. Relying only on foreign or optical data would leave gaps in coverage and in control over sensitive information. Building and operating its own SAR satellites gives India more control over tasking and data.

What are the RISAT satellites launched so far?

The RISAT satellites launched so far are RISAT-2 (2009), RISAT-1 (2012), RISAT-2B (2019), RISAT-2BR1 (2019), RISAT-2BR2 (2020) and RISAT-1A, also called EOS-04 (2022). All were launched by the Polar Satellite Launch Vehicle from the Satish Dhawan Space Centre at Sriharikota.

The dates above are stated to the month and should be treated as approximate, in line with ISRO’s published launch records. The names can cause confusion because some later satellites were also given the generic label EOS, for Earth Observation Satellite, in ISRO’s newer naming scheme.

What is RISAT-2 and why was it launched early?

RISAT-2 is an X-band radar imaging satellite launched in April 2009 on the PSLV, built around a radar payload of Israeli origin supplied by Israel Aerospace Industries. It was launched earlier than planned in India’s schedule following the November 2008 Mumbai attacks, because policymakers wanted a stronger surveillance capability quickly.

The reason for the change in order is straightforward. India’s own C-band satellite, RISAT-1, was still under development and needed more time, so the government decided to acquire a ready X-band radar from abroad and fly it on an Indian-built satellite bus. This allowed an operational radar imaging satellite to reach orbit years sooner.

The satellite was lighter than RISAT-1 and was launched into a low-inclination orbit, which suits observation of South Asia and nearby regions. Its imagery is widely reported to serve security and strategic needs, and details of its use and the resolution of its data are not released publicly in full. Reports speak of high-resolution imaging, but the precise figures should be treated as unconfirmed.

What is RISAT-1 and how is it different?

RISAT-1 is India’s first indigenously developed radar imaging satellite, launched in April 2012 on the PSLV, and it carries a C-band synthetic-aperture radar designed mainly for civilian uses such as agriculture, forestry and disaster management. It was a larger and more complex satellite than RISAT-2.

The C-band radar on RISAT-1 operated in several imaging modes with different resolutions and coverage, trading detail for the width of the area imaged. A notable feature was its use of a special polarisation scheme, known as hybrid polarimetry, which was relatively new for civilian remote sensing and was useful for studying vegetation and crops.

RISAT-1 supplied valuable data on kharif crops such as rice, which are grown in the monsoon when optical satellites struggle to see. It also helped mapping of floods and of forest cover. The satellite completed its mission life and was later retired, and its role was taken up by RISAT-1A (EOS-04), launched in 2022.

What are the RISAT-2B series satellites?

The RISAT-2B series, comprising RISAT-2B, RISAT-2BR1 and RISAT-2BR2, are X-band radar satellites launched between 2019 and 2020 that rely on an Indian-built radar and a large deployable antenna. They continued and expanded the capability first demonstrated by RISAT-2.

These satellites are significant for two reasons. First, they showed that India could build its own X-band SAR payload, reducing reliance on imported radar. Second, the launch of several satellites in quick succession improved how often a given area could be revisited.

Public statements from ISRO describe them in general terms as supporting agriculture, forestry and disaster management, while media and defence analysts widely report that they also strengthen military and border surveillance. The exact imaging resolution has not been fully published, and reported figures fall in the range of high-resolution X-band imaging. For that reason this article does not quote specific numbers.

What are the main uses of RISAT data?

The main uses of RISAT data are in agriculture, forestry, flood and disaster mapping, soil and water studies and, according to widely reported accounts, military and border surveillance. The ability to see through cloud makes the data especially valuable in the monsoon.

Agriculture

Radar images help identify crop type, track the growth of paddy and estimate the area sown, even in the wet season. Soil moisture can also be inferred from the radar signal, which is useful for drought assessment.

Forestry

Because radar signals interact with the structure of trees, RISAT data helps estimate forest cover and biomass and detect changes in forest areas.

Floods and disasters

Flood mapping is one of the best-known uses. Smooth floodwater appears dark in radar images, so the extent of inundation in states such as Assam and Bihar can be mapped quickly even while the sky is overcast. The data also supports landslide, cyclone and other disaster response.

Surveillance and security

The RISAT-2 series is widely reported to support military and border surveillance, including observation of terrain, infrastructure and maritime traffic. Official details are limited, as is normal for strategic assets.

How are RISAT satellites launched and operated?

RISAT satellites are launched by the Polar Satellite Launch Vehicle (PSLV) from the Satish Dhawan Space Centre in Sriharikota and are placed in low earth orbits a few hundred kilometres above the surface. The PSLV has been ISRO’s reliable launcher for earth-observation missions for several decades.

After launch, satellites are controlled from ISRO’s Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru. The raw radar signals are downlinked to ground stations, and the National Remote Sensing Centre (NRSC) in Hyderabad receives, processes and distributes the data. The satellites themselves are built by ISRO’s U R Rao Satellite Centre in Bengaluru and the Space Applications Centre in Ahmedabad, which develops the radar payloads.

Raw radar data is not directly interpretable, and so ground processing is a major step. Specialised software converts the recorded echoes into images, corrects for geometry and removes noise, after which analysts extract information about crops, floods or other targets.

How do RISAT satellites compare with optical satellites?

RISAT satellites differ from optical earth-observation satellites such as Cartosat and Resourcesat mainly in that they see through cloud and darkness, while optical satellites produce pictures closer to what the human eye sees but need daylight and clear skies. The two types are complementary and are often used together.

Radar images are generally harder to read for a non-specialist, because they show reflection of microwaves rather than colour. Analysts therefore often combine radar and optical data to get the best of both. This combined approach is common in disaster response and agricultural monitoring.

What is the future of radar imaging from India?

The future of radar imaging from India includes follow-on RISAT-class satellites, larger constellations, and international cooperation such as the NASA-ISRO Synthetic Aperture Radar (NISAR) mission, which was launched in 2025 to carry L-band and S-band radars. NISAR is a joint mission rather than a RISAT satellite, but it extends India’s radar capability to new bands and applications.

India has also encouraged private space companies to build small SAR satellites, and there is growing commercial interest in radar data for insurance, agriculture and infrastructure monitoring. Such developments are reported to be in progress, though details and timelines change quickly and should be verified from current sources.

Bottom Line

The RISAT satellites give India a dependable all-weather, day-and-night view of its territory through synthetic-aperture radar. RISAT-2 and the RISAT-2B series, in X-band, lean toward surveillance and strategic use, while RISAT-1 and RISAT-1A, in C-band, serve agriculture, forests and disaster management. Together they fill the gaps left by optical satellites, especially during the monsoon.

Frequently Asked Questions

What does RISAT stand for?

RISAT stands for Radar Imaging Satellite, the name of ISRO’s series of earth-observation satellites that carry synthetic-aperture radar. The radar lets the satellites image the ground through clouds, haze and darkness. The series includes RISAT-1, RISAT-2, RISAT-2B, RISAT-2BR1, RISAT-2BR2 and RISAT-1A.

Why was RISAT-2 launched before RISAT-1?

RISAT-2 was launched in 2009 before RISAT-1 because India wanted a radar surveillance satellite quickly after the 2008 Mumbai attacks, and RISAT-1 was still under development. RISAT-2 used an X-band radar of Israeli origin on an Indian-built satellite. RISAT-1, India’s first indigenous C-band radar satellite, followed in 2012.

How is RISAT different from Cartosat?

RISAT is a radar satellite that images through clouds and at night, while Cartosat is an optical satellite that takes high-resolution pictures in daylight and clear skies. RISAT data suits floods, monsoon crops and surveillance, whereas Cartosat data suits mapping and urban planning. The two are often used together.

What is RISAT used for?

RISAT is used for crop monitoring, forestry, flood and disaster mapping, soil moisture studies and, as widely reported, military and border surveillance. Its radar works in all weather, which makes it especially useful during the monsoon. Civilian users receive data through ISRO’s National Remote Sensing Centre.

Which rocket launches the RISAT satellites?

The RISAT satellites are launched by the Polar Satellite Launch Vehicle (PSLV) from Sriharikota in Andhra Pradesh. The PSLV places them in low earth orbit. It is ISRO’s long-serving workhorse for earth-observation and small satellite launches.

Is NISAR the same as RISAT?

NISAR is not a RISAT satellite but a separate joint radar mission between NASA and ISRO, launched in 2025, that carries L-band and S-band radars. RISAT is ISRO’s own series of radar imaging satellites. Both use synthetic-aperture radar and add to India’s radar-based earth observation capability.

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