Indian Remote Sensing Satellites: What IRS Can and Cannot Do

IRS stands for Indian Remote Sensing. These satellites look at the Earth and send back pictures and measurements. ISRO says their data serves agriculture, water, cities, minerals, forests, oceans and disasters.

When did the series begin?

IRS-1A was launched on 17 March 1988 from Baikonur in the Soviet Union. It was the first of the series. ISRO says it went into a polar sun-synchronous orbit. It carried two cameras, LISS-I and LISS-II.

How big is India’s fleet?

ISRO says India has one of the largest constellations of remote sensing satellites in operation. Do not write “the largest”. The word “one of” matters.

What is remote sensing in plain words?

Remote sensing means learning about a place without touching it. A satellite records the light or radio waves that bounce off the ground. Experts then read the records to study crops, water, forests and cities.

Think of IRS as a survey tool. It watches land, water and disasters. Telecom is not an IRS job, and traffic studies are not on ISRO’s list of IRS uses.

How is it used in farming?

NRSC uses satellite data for seasonal cropping patterns and yield-estimation experiments. It also estimates the net-sown area and studies agricultural drought. PIB says space technology gives fast and unbiased information about the crop situation.

How is it used for water and minerals?

NRSC has a geosciences group. It works on three areas. These are groundwater studies, mineral exploration and geohazards. Its mineral projects include diamond, iron, phosphate, manganese and bauxite. The Bhuvan Bhujal portal shows groundwater prospects and quality.

How is it used in disasters?

A 2025 reply in Parliament lists floods, cyclones, landslides, earthquakes and forest fires. It mentions about 300 flood inundation maps provided during 2024. RISAT data was used to assess the Wayanad landslide in July 2024.

Where else is it used?

• Cartosat 2S and 3 data supports the PMKSY watershed programme.
• Rural roads under PMGSY are mapped on Bhuvan.
• NRSC water studies help plan and monitor irrigation projects.

ISRO says IRS-1A went into a polar sun-synchronous orbit. Most IRS satellites follow the same plan. Resourcesat-1 flies at 817 km. Its local crossing time is 10.30 a.m.

What is a sun-synchronous orbit?

ESA calls it a polar orbit in which the satellite stays in sync with the Sun. The satellite passes over the same spot at the same local time every day. ESA says it usually flies between 600 and 800 km.

Why does this suit a mapping satellite?

The sun angle stays similar on every pass. So pictures taken on different dates are easy to compare. ESA says polar orbits are useful for global coverage.

How is that different from a communication satellite?

A telecom satellite must stay fixed above one place. ESA says the geostationary orbit suits this. It lies at 35,786 km above the equator. The INSAT system uses it.

Is it always polar?

No. EOS-05 is India’s first imaging satellite in geosynchronous orbit. ISRO’s home page says it was launched on 4 September 2026. So “typically polar” is the right wording, not “always polar”.

Resolution is the size of the smallest patch on the ground that one pixel can show. A small number means a sharper picture. A big number means a coarse one.

What is the resolution ladder?

• AWiFS on Resourcesat-1 has a 56 m resolution and a swath of 737 km.
• LISS-III has a 23.5 m resolution in the visible and near-infrared bands.
• LISS-IV has a 5.8 m resolution at nadir.
• Cartosat-1 has a 2.5 m resolution. ISRO calls it the first Indian remote sensing satellite able to give in-orbit stereo images.
• Cartosat-2A and 2B are better than 1 m.
• Cartosat-3 gives 0.28 m in the panchromatic band and 1.12 m in four multispectral bands.

What is the trade-off?

A sharper camera usually sees a narrower strip. AWiFS covers 737 km. Cartosat-3 has a nominal swath of about 17 km. Coarse sensors suit wide jobs like crop patterns. Sharp sensors suit city maps and planning.

Where is Cartosat-3 used?

ISRO lists large-scale urban planning, rural resource and infrastructure development and coastal land use. PIB says it was launched on 27 November 2019 into a 509 km sun-synchronous orbit.

A camera satellite is called optical. It records sunlight that bounces off the ground. NASA says optical instruments collect visible, near-infrared and short-wave infrared light.

What does a radar satellite do?

A radar satellite sends its own radio waves and records the echo. NASA says SAR makes images night or day, regardless of weather. Its long wavelengths can see through clouds and dense tree canopy.

Which Indian satellites carry radar?

• RISAT-1 carries a C-band SAR. ISRO says it images the surface by day and night in all weather.
• RISAT-2 is a radar imaging satellite with all-weather capability.
• EOS-04 is a radar imaging satellite for farming, forestry, soil moisture and flood mapping.
• NISAR carries both NASA’s L-band and ISRO’s S-band SAR. ISRO says it gives all-weather, day and night data.

What is the lesson for an exam?

Radar works night or day, whatever the weather. RISAT-1 is used for paddy monitoring in the kharif season and for floods and cyclones.

Indian earth observation satellites can be sorted into families. The names often hint at the job.

What are the main families?

• IRS-1A, 1B, 1C and 1D are the early operational satellites, from 1988 to 1997.
• Oceansat (IRS-P4) was launched on 26 May 1999. ISRO says it was the first satellite built mainly for ocean applications.
• Resourcesat-1 followed in 2003. Resourcesat-2 followed in 2011.
• Cartosat is the mapping family. Cartosat-1 flew in 2005. Cartosat-3 flew in 2019.
• RISAT is the radar family. RISAT-1 flew in 2012.
• ISRO now uses the EOS name for new satellites. EOS-04 and EOS-06 are examples.

What went wrong in the early years?

IRS-1E was launched on 20 September 1993 on the first PSLV flight. Its payloads could not be placed in orbit. ISRO’s table marks the launch as unsuccessful.

What is new?

EOS-06 is the third-generation Oceansat. EOS-05 is India’s first imaging satellite from geosynchronous orbit. The ISRO home page lists its launch as 4 September 2026.

NRSC is the National Remote Sensing Centre in Hyderabad. It receives, processes and shares IRS data. The data reception station is at Shadnagar. The administration and applications work is at Balanagar.

Where can people get the data?

Bhoonidhi is NRSC’s data portal. It hosts products from IRS and foreign satellites. Its coverage is mainly India and the area around it. Bhuvan is ISRO’s geoportal for maps and layers.

What does the Indian Space Policy 2023 say?

• Data with a ground sampling distance of 5 metres or coarser is to be free and open to all.
• Data finer than 5 metres is free for government entities. Non-government entities pay fair and transparent prices.
• Very high resolution data, at 30 cm or finer, needs IN-SPACe authorisation for dissemination. It is a national security rule.

An older rule was named in Bhoonidhi’s 2022 pricing guide. It is the Remote Sensing Data Policy of 2011. It asks that orders for data of 1 m and finer be vetted.

IRS is for observing the Earth. Telecom is done by communication satellites such as INSAT. ISRO’s list of IRS applications names agriculture, water, planning, minerals, forests, oceans and disasters. Telecommunications and traffic studies are not on it.

What did UPSC ask in 2015?

UPSC Prelims 2015, Q71 (Series A), asked about five activities. They were crop productivity, groundwater, mineral exploration, telecommunications and traffic studies. The task was to pick where IRS satellites are used.

Options 1, 2 and 3 are real IRS uses. Options 4 and 5 are not on ISRO’s list of IRS uses. So the answer is (a), 1, 2 and 3 only. UPSC’s official key for Series A also gives (a).

What did UPSC ask in 2019?

UPSC Prelims 2019, Q32 (Series A), asked what satellite images or remote sensing data can measure. The items were chlorophyll in vegetation, greenhouse gas emissions from rice paddies and land surface temperature. UPSC’s official key for Series A gives (d), 1, 2 and 3.

How can you avoid the trap?

Ask what the satellite does. If it looks at the ground, think IRS. If it carries signals, think INSAT.