Indian Remote Sensing satellites

Also called: Indian Remote Sensing Satellite System, IRS · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 11, Ch 6 "Introduction to Remote Sensing"; Class 12, Ch 7 "Transport and Communication"

Meaning

Indian Remote Sensing (IRS) satellites are India's main series of Earth observation satellites. They carry multispectral sensors, which record the same scene in several wavebands, to collect data for managing natural resources, farming, forests, water and disasters. The series began with IRS-1A, launched on 17 March 1988 from Baikonur. IRS took India from small experimental satellites to a full fleet of its own, and it has built a land record that goes back to 1988.

Explanation

How an IRS satellite "sees" the earth

• Sensor: an instrument that records the energy that the earth reflects or gives off.
• Optical (passive) sensing: IRS cameras record sunlight reflected from the ground.
• Crops, water, soil and forest each reflect the blue, green, red and near-infrared bands in a different way.
• Comparing the bands tells these features apart.

• Because these sensors depend on sunlight, they need daylight and clear skies.

• LISS (Linear Imaging Self-Scanning sensor): the multispectral pushbroom camera used on IRS satellites.

• Pushbroom means a long row of detectors lies across the satellite's path. It records a whole line of ground at once, and the line moves forward as the satellite moves, like a broom sweeping a floor.

• It has no moving mirror. So its images are steadier and sharper than those of the older whiskbroom (scanning-mirror) sensors, such as Landsat's MSS.

• PAN (panchromatic) sensor: records one broad band, which gives a black-and-white image. It is usually sharper than the multispectral bands on the same satellite.

• Orbit: like most Earth observation satellites, IRS-type satellites fly in a sun-synchronous polar orbit (SSPO).
• This is a near-polar orbit about 500–900 km high.
• The satellite crosses each place at the same local time on every pass, so the sunlight is the same in every image.
• Result: fine ground detail, but the satellite comes back over the same place only every few days.

Stages of growth

Stage 1: Bhaskara (the experiments)

• Bhaskara-I (1979) and Bhaskara-II (1981) were India's first experimental Earth observation satellites. Both flew on Soviet rockets.
• They carried TV cameras for images of land, water and forest. They also carried microwave radiometers (passive sensors that measure the natural microwave energy given off by the surface) for the ocean and the atmosphere.
• Result: India learned how to build sensors, receive the data and use it. This prepared the way for IRS.

Stage 2: the IRS series

Satellite	Year	Sensors and resolution
IRS-1A	1988	LISS-I (72.5 m), LISS-II (36.25 m)
IRS-1C	1995	LISS-III (23 m), PAN (5.8 m)
Resourcesat-1 (IRS-P6)	2003	LISS-III, LISS-IV, AWiFS

• Spatial resolution is the size of the smallest patch of ground that one pixel shows. A smaller number means a sharper image.
• The trend: each new generation gave sharper images, going from 72.5 m to 36.25 m, then 23 m, then 5.8 m PAN.

Stage 3: satellites for special jobs

• Resourcesat (land and crops): Resourcesat-1 (IRS-P6, 2003) carried three cameras on one satellite:
• AWiFS (Advanced Wide Field Sensor): a wide but coarse view, good for state-level crop estimates.
• LISS-III: a medium view.
• LISS-IV: a sharp, narrow view, good for single fields and villages.

• Resourcesat-2 and Resourcesat-2A continue the same work.

• Cartosat (maps):

• Cartosat-1 (2005) took stereo pairs: two images of the same place taken from two angles, like our two eyes. These give a sense of height.
• From stereo pairs we make DEMs (Digital Elevation Models: 3D maps of land height). DEMs are used for contour maps, road and dam planning, and watershed mapping.

• Cartosat-3 (2019) reaches about 25 cm resolution. That is enough to see single vehicles and the outlines of buildings.

• Oceansat (the ocean):

• It maps chlorophyll (the green pigment in phytoplankton, the tiny plants in the ocean), which shows where fish food is plentiful.
• It maps potential fishing zones (PFZ), which are advisories telling fishers where fish are likely to gather.
• It maps sea-surface winds, which help cyclone and monsoon forecasts.

• Oceansat-3 (EOS-06) was launched in 2022.

• RISAT (radar): India's C-band SAR satellites.

• SAR (Synthetic Aperture Radar) is a side-looking radar. It sends out its own microwave pulses and records the echo. It joins the echoes from many points along the orbit, so they act like one very long antenna.
• C-band has a wavelength of about 5.6 cm. It is good for crops, floods and sea ice.
• RISAT-1 was launched in 2012 and EOS-04 (RISAT-1A) in 2022.

Why India needs both optical and radar satellites

• The monsoon problem:
• Most floods and kharif crops come during the south-west monsoon (June–September).

• Thick cloud then covers the country, so optical cameras like LISS see little.

• The radar answer:

• Microwaves pass through cloud and do not need sunlight.

• So RISAT can map floodwater and paddy fields even at night and under monsoon cloud.

• Result: using optical and radar satellites together gives coverage in every season.

Where it occurs

• Launch sites: IRS-1A was launched from Baikonur (in Kazakhstan, then part of the USSR). The earlier Bhaskara satellites also flew on Soviet rockets. Later, India moved to a full fleet that it builds and launches itself.
• Who runs it: ISRO (Indian Space Research Organisation) runs the IRS series, from IRS-1A in 1988 onwards.
• Farming across India: AWiFS gives crop estimates for whole states. LISS-IV shows single fields and villages. NCERT Fig. 6.11 shows a Resourcesat image.
• Coasts and seas: Oceansat sends PFZ advisories to fishers and gives sea-wind data for cyclone and monsoon forecasts.
• Flood-prone plains: radar satellites (RISAT/EOS-04) can map monsoon floods, for example in Assam and Bihar, and estimate kharif paddy area.
• Cities and land records: Cartosat-3's 25 cm images help with city planning, cadastral (land-record) maps and defence. Cartosat-1's DEMs help plan roads, dams and watersheds.
• Borders: RISAT is also used for border surveillance (watching the borders).
• Tracking change: the IRS record since 1988 helps track deforestation, glacier retreat, city growth and wetland loss. These records support forest cover reports, watershed planning and climate adaptation.

Don't confuse with

• Landsat: a USA programme run by NASA and USGS. It began in 1972 as ERTS-1 and holds the longest continuous land record. IRS is India's programme and began in 1988.
• Bhaskara-I and II (1979, 1981): these were experimental satellites with TV cameras and microwave radiometers. IRS-1A (1988) was the first satellite of India's working series.
• INSAT-3DS: a geostationary weather satellite. It sits about 35,786 km above the equator and watches the same area all the time. It was funded by MoES [5]. IRS satellites fly in low sun-synchronous polar orbits: they show fine ground detail but revisit only every few days.
• NISAR: a joint NASA–ISRO satellite and the first to carry both L-band and S-band radar. NASA gave the L-band radar and the 12 m antenna. ISRO gave the S-band radar, the bus and the GSLV-F16 rocket [2]. RISAT, by contrast, is India's own C-band radar.

Prelims Hooks

• IRS-1A was launched on 17 March 1988 from Baikonur, not Sriharikota. Its sensors were LISS-I (72.5 m) and LISS-II (36.25 m).
• LISS resolution order: LISS-I 72.5 m → LISS-II 36.25 m → LISS-III 23 m. IRS-1C (1995) also carried PAN 5.8 m.
• Resourcesat-1 = IRS-P6 (2003). It carried AWiFS + LISS-III + LISS-IV and is used for crops.
• Match each satellite to its job: Cartosat → mapping and DEM (Cartosat-1 stereo, 2005; Cartosat-3 ≈ 25 cm, 2019). Oceansat → PFZ and chlorophyll (Oceansat-3 = EOS-06, 2022). RISAT → C-band SAR (RISAT-1 in 2012; EOS-04 = RISAT-1A in 2022).
• LISS is a pushbroom sensor with no moving mirror. Landsat's MSS is a whiskbroom (scanning-mirror) sensor. This is a common trap.
• Bhaskara-I (1979) and Bhaskara-II (1981) were experimental and flew on Soviet rockets. They came before the IRS series.

Mains Points

• From experiment to self-reliance (GS-III, science and technology):
• India moved from Bhaskara on Soviet rockets and IRS-1A from Baikonur to its own fleet: Resourcesat, Cartosat, Oceansat and RISAT.
• These satellites now serve crop forecasts, fishing advisories and cadastral mapping.

• NISAR shows India is now an equal partner in the world's top Earth observation missions [2].

• Radar fills the monsoon gap (GS-III, disasters and agriculture):

• Optical IRS images fail under monsoon cloud, which is exactly when floods and kharif sowing happen.
• C-band RISAT/EOS-04 gives flood maps and paddy estimates in all weather.

• The loss of the radar satellite EOS-09 on PSLV-C61 (18 May 2025, a 3rd-stage problem) [3] shows why India needs backup satellites to keep radar coverage running.

• Long archives for planning (GS-I and III):

• The IRS record since 1988 can be read alongside Landsat's record since 1972 [4].
• Together they let India measure deforestation, glacier retreat, city growth and wetland loss, which supports forest reports, watershed planning and climate adaptation.

Related concepts

• Landsat
• SPOT
• Sentinel satellites
• Bhaskara satellites
• LISS
• Resourcesat
• Cartosat series
• Oceansat
• RISAT
• INSAT-3DS

Read more

• Earth observation satellites: the world and India