Indian Remote Sensing Satellites Explained

Indian remote sensing satellites form one of the largest civilian Earth-observation constellations in the world, a fleet of spacecraft that watches farms, forests, rivers, cities, coastlines and glaciers from orbit and sends the data back to ground stations in India. Built and launched by the Indian Space Research Organisation (ISRO), the Indian Remote Sensing (IRS) programme began in 1988 and has since grown into a family of satellites with different eyes: optical cameras, radar imagers and ocean sensors.

The purpose of the programme is practical rather than prestigious. A farmer’s crop estimate, a flood map, a groundwater survey, a city’s land-use plan or a fisherman’s advisory may all depend on images taken from a satellite hundreds of kilometres above the ground. This article explains what remote sensing is, how the IRS programme developed, the main satellite series such as Resourcesat, Cartosat, RISAT and Oceansat, their applications, and how the data reaches users through the National Remote Sensing Centre.

What Is Remote Sensing?

Remote sensing is the science of gathering information about an object or area without touching it. A satellite does this by recording electromagnetic radiation, such as visible light, infrared, microwave or thermal radiation, that is reflected or emitted from the Earth’s surface. Different materials reflect radiation differently, so healthy vegetation, bare soil, water, snow and concrete each leave a distinct signature.

Passive and Active Sensors

Optical satellites are passive sensors, which record sunlight reflected from the surface. They produce pictures that are easy to interpret but they cannot see through clouds or work at night. Radar satellites are active sensors, which send their own microwave pulses and record the echo. Because microwaves pass through cloud, rain and darkness, radar imaging is valuable during the monsoon and for disaster response.

Resolution

Three types of resolution matter. Spatial resolution is the size of the smallest ground feature a pixel represents. Spectral resolution is the number and width of the wavelength bands recorded. Temporal resolution is how often the satellite revisits the same place. Different missions are optimised differently: a crop-monitoring satellite favours wide coverage and frequent revisits, while a city-mapping satellite favours fine detail.

Origins of the IRS Programme

India’s interest in remote sensing began even before it had its own operational satellites. In the 1970s, experiments were conducted using aircraft and balloons, and the country established a National Remote Sensing Agency in Hyderabad in the 1970s, which later became the National Remote Sensing Centre. ISRO then launched two experimental satellites, Bhaskara-1 in 1979 and Bhaskara-2 in 1981, which carried cameras to study land and ocean, and they provided early experience.

The vision, driven by the early leaders of the space programme such as Vikram Sarabhai and Satish Dhawan, was that space technology should be used for national development. A dedicated remote sensing satellite system was the natural next step. The result was the IRS series, designed to be an operational system with a regular supply of data to many users.

The First Generation: IRS-1A to IRS-1D

IRS-1A was launched on 17 March 1988 on a Soviet Vostok rocket from Baikonur, and it was followed by IRS-1B in 1991. Both carried the Linear Imaging Self-Scanning cameras, known as LISS, which provided moderate-resolution multispectral images. These satellites proved that India could build and operate a civilian Earth-observation system and they established the practice of free, regular data supply for national purposes.

Further Milestones

• IRS-1C, launched in 1995, introduced a panchromatic camera with higher resolution and a wide-field sensor, which made the Indian system among the best of its time for civilian use
• IRS-P2, launched in 1994 on the second developmental flight of the Polar Satellite Launch Vehicle, was an early satellite of the programme launched from Indian soil
• IRS-1D followed in 1997 and was launched by the PSLV, strengthening the constellation
• IRS-P3, launched in 1996, carried instruments for studying the atmosphere and ocean, as well as X-ray astronomy

The shift from foreign launchers to the home-grown PSLV was a turning point, because it gave India control over the launch schedule and made the PSLV the workhorse of the programme.

Resourcesat: The Multispectral Workhorse

The Resourcesat series is designed for natural-resource monitoring, particularly agriculture and forestry. Resourcesat-1, also known as IRS-P6, was launched in 2003. It was followed by Resourcesat-2 in 2011 and Resourcesat-2A in 2016, which maintained and improved the continuity of data.

Sensors on Board

• LISS-IV, a high-resolution multispectral camera, which offers a spatial resolution of a few metres
• LISS-III, a medium-resolution multispectral camera, which covers a wider swath
• AWiFS, the Advanced Wide Field Sensor, which covers a very wide swath and revisits the same area frequently, making it ideal for tracking crop cycles over large regions

Together these cameras let analysts map crop types, estimate acreage, assess vegetation health, monitor forest cover and track changes in land use. Resourcesat data has been used for national crop forecasting programmes, wasteland mapping and many state-level projects.

Cartosat: Eyes for High-Resolution Mapping

The Cartosat series is intended for cartography, urban and rural planning, infrastructure development and land information systems. Cartosat satellites carry panchromatic cameras that can see fine detail, and some of them can be steered to look at different angles to collect stereo images used for making three-dimensional terrain models.

Key Missions

• Cartosat-1, launched in 2005, carried two cameras that provided stereo pairs and was used for terrain mapping and elevation models
• Cartosat-2, launched in 2007, offered sub-metre resolution and the ability to point the camera, and it was followed by several satellites in the same series
• The Cartosat-2 series expanded through the following years to provide frequent, detailed imagery
• Cartosat-3, launched in November 2019, is the most advanced of the series, with a resolution of the order of a quarter of a metre, among the sharpest of any civilian satellite at the time

These satellites support town planning, road alignment, utility mapping, border and coastal surveys, and the creation of precise maps for infrastructure planning and property records. They also have uses in defence and security under controlled arrangements.

RISAT: Radar Imaging Through Clouds

The Radar Imaging Satellite, or RISAT, series gives India an all-weather, day-and-night imaging capability. Optical satellites are limited by cloud cover, which is a particular problem during the Indian monsoon, when much of the country is cloudy for weeks. Synthetic aperture radar solves this by producing an image from microwave echoes.

Milestones

• RISAT-2, launched in 2009, was an X-band radar satellite developed with Israeli collaboration and used for surveillance and disaster monitoring
• RISAT-1, launched in 2012, was India’s first indigenously developed C-band synthetic aperture radar satellite, useful especially for agriculture and flood monitoring in the monsoon
• RISAT-2B and RISAT-2BR1, launched in 2019, extended the X-band radar capability
• RISAT-1A, launched in 2022 under the EOS naming scheme as EOS-04, continued the series

Radar data is especially valuable for flood mapping, soil moisture estimation, crop monitoring of rice grown in cloudy seasons, ship and ocean-surface observation, and the detection of land subsidence.

Oceansat and Other Specialised Satellites

The ocean is the focus of the Oceansat series. Oceansat-1, also called IRS-P4, was launched in 1999. Oceansat-2 followed in 2009 and Oceansat-3, also named EOS-06, was launched in November 2022. These satellites carry an ocean colour monitor that measures the colour of the sea surface, from which scientists estimate chlorophyll concentration, which indicates the presence of phytoplankton and hence of fish. They also include scatterometers to measure the speed and direction of winds near the surface.

Uses of Ocean Data

• Potential fishing zone advisories for fishermen, issued by the Indian National Centre for Ocean Information Services
• Monitoring of algal blooms and the health of coastal waters
• Cyclone tracking, supported by wind-vector data
• Study of sea-surface temperature and ocean currents

Other Earth-Observation Missions

Beyond the main series, ISRO has flown other satellites for observation. Megha-Tropiques, a joint mission with France, studies the tropical water cycle. SARAL, also with France, measures sea-surface height. The INSAT-3D weather satellites serve meteorology from geostationary orbit. In recent years, ISRO has started grouping its observation satellites under the EOS designation, and a joint NASA-ISRO radar mission called NISAR was launched in 2025 to study the Earth’s changing surface.

Applications of Indian Remote Sensing Satellites

Remote sensing data has become an essential input for governance. The principal application areas are summarised below.

Agriculture and Food Security

Satellite monitoring helps estimate area under major crops before harvest and flags stress from drought or pests, giving policy-makers early signals. Programmes for forecasting agricultural output using space, agro-meteorology and land-based observations draw heavily on IRS data.

Disaster Management

During floods, cyclones and landslides, satellites provide a quick, broad view of the affected area. Radar images are particularly useful because they can be acquired through cloud. Agencies use these maps to plan relief, locate stranded communities and assess damage.

Water, Urban Planning and Infrastructure

Water management is a major use of remote sensing. Satellites map surface water bodies, monitor the filling and drying of reservoirs, measure snow and glacier cover in the Himalaya and support groundwater prospecting maps used by government programmes for drinking water. Multi-year comparisons reveal how lakes and wetlands are shrinking or growing.

In urban planning, high-resolution images from Cartosat help prepare base maps for master plans, track unplanned growth and map utilities. They are used in programmes for property mapping in villages with the help of drones and satellite images, and in the planning of roads, railways, ports and industrial corridors. Large national platforms for infrastructure planning also integrate satellite layers to avoid duplication and to speed up the alignment of projects.

Data Distribution: NRSC and Bhuvan

The National Remote Sensing Centre, based at Balanagar in Hyderabad, is the ISRO centre responsible for acquiring, processing and distributing remote sensing data. It operates the ground station at Shadnagar, near Hyderabad, where data from the satellites is received, and it runs data processing, analysis and training facilities. Data from the Indian satellites is also received at overseas stations under agreements, and global users can obtain Indian data through licensed distributors.

Access Channels

• Bhuvan, ISRO’s geoportal, which offers satellite images, maps and thematic layers for public viewing and use
• Bhoonidhi, a portal for searching and downloading satellite data products
• Decision support services for disasters, delivered through the National Database for Emergency Management
• Training programmes through institutes associated with ISRO, such as the Indian Institute of Remote Sensing in Dehradun

Data policy has become more open over time. Many datasets are available free of charge for public use, particularly lower-resolution data, while sensitive high-resolution products may be regulated.

Challenges and the Future

India’s remote sensing system faces the normal challenges of an ageing constellation that needs continuous replacement, the demand for ever-higher resolution and shorter revisit times, and the need to convert large volumes of data into easy-to-use information. Artificial intelligence and cloud computing are increasingly used to process images quickly.

Another change is the arrival of private companies in Earth observation. With the opening of the space sector and the creation of IN-SPACe, Indian start-ups have begun building small satellite constellations, including hyperspectral imaging satellites, which may complement ISRO’s missions. ISRO continues to plan new observation satellites with better sensors, and the joint NISAR mission demonstrates a growing role in international cooperation.

Conclusion

From IRS-1A in 1988 to the sharp-eyed Cartosat-3 and the radar and ocean satellites of today, Indian remote sensing satellites have given the country the ability to observe itself regularly and in detail. They support farmers, planners, scientists and disaster managers, and they are a clear example of space technology serving everyday development. With new satellites and private participation, the programme is expected to remain a core part of India’s space and governance infrastructure.

Frequently Asked Questions

What are Indian remote sensing satellites?

They are Earth-observation satellites built and launched by ISRO under the Indian Remote Sensing programme. They carry optical, radar and ocean-monitoring instruments that capture images and data for agriculture, water, mapping, disaster management and other uses.

When was the first IRS satellite launched?

IRS-1A, the first operational satellite of the series, was launched on 17 March 1988 from Baikonur, then in the Soviet Union. Later satellites were launched mostly by India’s own PSLV from Sriharikota.

What is the difference between Cartosat and RISAT?

Cartosat satellites are optical satellites that take very sharp pictures for mapping and planning, but need daylight and clear skies. RISAT satellites use synthetic aperture radar, which can image the ground through clouds, rain and darkness.

What is Resourcesat used for?

Resourcesat satellites carry multispectral cameras called LISS-III, LISS-IV and AWiFS. They are used mainly to monitor crops, forests, land use and water resources over large areas, with frequent revisits.

What does the National Remote Sensing Centre do?

The National Remote Sensing Centre in Hyderabad is the ISRO centre that receives, processes and distributes data from Indian remote sensing satellites. It also develops applications, runs the Bhuvan portal in association with ISRO and provides disaster-support services.

How does satellite data help in disasters?

Satellite images show flooded areas, cyclone damage, landslides and fires quickly and across wide regions. Radar images are particularly useful during the monsoon because they can see through cloud, and the maps help agencies plan relief and rescue work.