The Cartosat Satellites Explained

Cartosat is India’s series of high-resolution optical earth-observation satellites, built by the Indian Space Research Organisation (ISRO) as part of the Indian Remote Sensing (IRS) family to capture detailed imagery for cartography, urban and infrastructure planning, and terrain analysis. The Cartosat satellites carry panchromatic cameras that photograph the ground in fine detail, and they have moved from a few metres of resolution in the first satellite to well below one metre in later generations.

The Cartosat series was launched on the Polar Satellite Launch Vehicle (PSLV) into sun-synchronous polar orbits, which allows each satellite to image the same place at a consistent local time. This explainer covers the satellites in the series, their cameras, how their imagery is used and the strategic role widely reported for the higher-resolution members.

Key Takeaways

• Cartosat is an ISRO series of optical earth-observation satellites designed for high-resolution cartographic mapping.
• Cartosat-1, launched in 2005, carried two panchromatic cameras that gave stereo images for generating three-dimensional terrain data.
• The Cartosat-2 series, beginning in 2007, brought sub-metre resolution and agile, steerable imaging to the Indian programme.
• Cartosat-3, launched in 2019, is the third-generation satellite with resolution of a few tens of centimetres and additional spectral capability.
• Every Cartosat satellite has been launched by the Polar Satellite Launch Vehicle (PSLV), ISRO’s reliable workhorse for polar orbits.
• Cartosat imagery supports urban planning, infrastructure design, cadastral mapping and terrain modelling, and the higher-resolution satellites are also widely reported to serve strategic surveillance needs.

What are the Cartosat satellites?

The Cartosat satellites are a series of Indian remote-sensing spacecraft optimised for cartography, which means the making of accurate maps. They are distinguished from other IRS satellites, such as the Resourcesat series, by their high spatial resolution rather than a wide coverage of land and vegetation.

In a typical remote-sensing system there is a trade-off between detail and coverage. Wide-swath satellites such as Resourcesat see large regions at moderate detail, which suits crop and forest monitoring. Cartosat satellites look at smaller strips of land in much finer detail, which suits the mapping of roads, buildings, plots and terrain.

The cartographic satellites form part of the national remote sensing programme coordinated by ISRO and used by agencies across the central and state governments. Data distribution has been handled by the National Remote Sensing Centre (NRSC) in Hyderabad.

How did the Cartosat programme begin with Cartosat-1?

The Cartosat programme began with Cartosat-1, also known as IRS-P5, which was launched in May 2005 on a PSLV and carried two panchromatic cameras pointed forward and aft to take stereo pairs of images. Each camera gave a resolution of about two and a half metres, and together they covered a swath of roughly 30 km.

The idea of the stereo pair is the same as human binocular vision. Two images of the same ground taken from different angles allow software to calculate the height of terrain and buildings. From these pairs, ISRO produced digital elevation models and orthoimages, which are maps corrected for terrain distortion. A national terrain product known as CartoDEM came out of this work.

Cartosat-1 was important because it gave India a domestic source of stereo imagery for large-scale mapping, reducing the need to rely on foreign satellites. It remained useful well beyond its originally planned lifetime.

What is the Cartosat-2 series?

The Cartosat-2 series is a group of Indian remote-sensing satellites launched from 2007 onwards that carry a single panchromatic camera with a resolution finer than one metre. The satellites in the group are designated Cartosat-2, 2A, 2B, 2C, 2D, 2E and 2F, and they were launched over roughly a decade.

A key feature of the series is agility. The satellite body can be steered, or the camera tilted, so that the camera can look sideways or forward of the track and revisit a target of interest more often than a satellite that can image only straight down. This allows imaging on demand and the collection of stereo pairs from a single satellite.

Some of these launches carried many smaller satellites from other countries as co-passengers. The 2017 launch of Cartosat-2D, for example, became famous because the PSLV placed a record number of satellites in orbit in one mission, and the PSLV’s ability to deploy multiple payloads in different orbits is a notable part of its reputation.

What is Cartosat-3?

Cartosat-3 is the third-generation Cartosat satellite, launched in November 2019 by the PSLV, and it provides imagery with a panchromatic resolution of a few tens of centimetres, which is the finest civil optical resolution achieved by an Indian satellite. The satellite also has a multispectral capability and flies at a lower altitude than the earlier ones, which helps in finer imaging.

The improvements include a larger telescope, a more advanced detector system, high-agility pointing and a high-rate data link. Cartosat-3 is much heavier than earlier Cartosats because of its bigger optical system and higher power needs. Its swath is narrower than that of Cartosat-1, which is the usual cost of increased detail.

The satellite was launched along with a set of small commercial satellites from another country, in keeping with the PSLV’s practice of carrying co-passengers. Further follow-on satellites in the Cartosat-3 class have been discussed in ISRO plans, although launch dates are subject to change.

How do the Cartosat cameras work?

The Cartosat cameras work as push-broom optical scanners, which form an image line by line as the satellite moves along its orbit. A telescope focuses light from the ground onto a long row of detectors, and the forward motion of the satellite sweeps this row across the surface to build up a continuous strip of imagery.

Panchromatic and multispectral imaging

A panchromatic camera records the total brightness across a wide band of visible and near-infrared light, producing a black-and-white image of high detail. A multispectral camera splits the light into a few colour bands, such as red, green, blue and near-infrared, at a coarser resolution. In practice, analysts often combine the two in a process called pan-sharpening, which gives a colour image with fine detail.

Stereo imaging and agility

Cartosat-1 used two separate cameras with different viewing angles to take stereo pairs within the same orbit pass. The Cartosat-2 and Cartosat-3 satellites rely on agile pointing, so that the satellite can image the same place from different angles during one or two passes.

Ground processing

Imagery is transmitted to ground stations, corrected for geometry and radiometry, and supplied as standard products. Because the high-resolution images are large, data handling and storage form a significant part of the system.

What is the orbit of the Cartosat satellites?

The Cartosat satellites move in sun-synchronous polar orbits, which pass near the poles and cross the equator at nearly the same local solar time on each pass. This means shadows and lighting remain similar from one image to the next, which makes comparison of scenes over time easier.

The altitude varies by satellite. Cartosat-1 and the Cartosat-2 series fly at roughly 600 to 650 km, while Cartosat-3 flies lower, near 500 km, to improve resolution. Because the Earth rotates beneath the orbit, each satellite sweeps over different strips of ground on successive days, and its revisit time for a given place depends on orbit repeat cycle and sideways pointing. Agile satellites can revisit specific targets in a few days.

What are the main uses of Cartosat imagery?

Cartosat imagery is used mainly for large-scale mapping, urban and infrastructure planning, cadastral work and terrain analysis. The high detail allows individual buildings, roads, canals and plots to be identified, which is not possible at coarser resolutions.

Principal civilian applications include:

• Cartography and base maps: Updating topographic maps at large scales and creating base layers for geographic information systems.
• Urban planning: Monitoring growth, mapping slums and road networks, and supporting master plans for towns and cities.
• Infrastructure planning: Selecting alignments for roads, railways, canals and power lines, and monitoring construction progress.
• Cadastral mapping: Supporting land record maps and property surveys, where fine detail helps in marking plot boundaries.
• Terrain and hydrology: Producing digital elevation models for flood modelling, watershed analysis and slope studies.
• Disaster response: Assessing damage after floods, earthquakes, landslides or cyclones with before-and-after images.
• Rural development: Mapping village assets, water bodies and land use for planning schemes.

What is the strategic role of the Cartosat satellites?

The higher-resolution Cartosat satellites are widely reported to serve strategic and surveillance needs, because detailed optical imagery has obvious value for monitoring borders, coastlines and military infrastructure. Official ISRO statements usually emphasise civilian applications, while media and defence analysts note the dual-use character of high-resolution imaging.

Imaging satellites are generally considered dual-use assets. The same picture that helps plan a road may also help identify a facility. Reports have linked the Cartosat-2 series with the needs of the armed forces, and a series of Indian launches of such satellites has often been discussed alongside border security and strategic awareness. Dedicated military imaging satellites also exist in India’s inventory, so Cartosat should be viewed as part of a wider system.

It is important to rely on official sources for details, because specifics of tasking and use are not generally published.

How does Cartosat compare with other Indian earth-observation satellites?

Cartosat differs from other Indian earth-observation satellites by focusing on very high spatial resolution over narrow swaths, while other series focus on wide coverage, radar imaging or ocean and weather observation. The comparison below summarises the main families.

Together these families form the Indian Remote Sensing system, one of the largest civilian remote-sensing constellations in the world. Optical, radar and meteorological data complement each other, since clouds block optical sensors but not radar.

Who builds and operates the Cartosat satellites?

The Cartosat satellites are designed and operated by ISRO, with different centres sharing the work. The U R Rao Satellite Centre in Bengaluru builds the satellite platform, the Space Applications Centre in Ahmedabad develops key payload elements and imaging applications, and the Vikram Sarabhai Space Centre develops the launch vehicle.

Launches take place from the Satish Dhawan Space Centre (SDSC SHAR) at Sriharikota, and the satellites are tracked and controlled by the ISRO Telemetry, Tracking and Command Network (ISTRAC). Imagery is received at ground stations such as those of the National Remote Sensing Centre, which processes and distributes data to users through standard channels and geoportals such as Bhuvan.

What is the future of the Cartosat series?

The future of Cartosat points towards even finer resolution, more frequent revisit and a larger role for the private sector in earth observation. ISRO has discussed follow-on satellites in the Cartosat-3 class, and the opening up of the Indian space sector has encouraged private companies to build small imaging satellites and constellations.

The aim of greater revisit is to monitor change more continuously, which can be achieved with constellations of multiple satellites. Newer sensing technologies, including hyperspectral imaging and onboard processing, may also complement the traditional optical cameras. Whatever the specific future launches, Cartosat’s core contribution remains the same: it has given India a domestic supply of detailed imagery for national planning.

Bottom Line

The Cartosat satellites are the high-resolution optical backbone of India’s remote-sensing programme. From the stereo cameras of Cartosat-1 to the sub-metre Cartosat-2 series and the finer Cartosat-3, they support mapping, urban and infrastructure planning, and are widely reported to serve strategic needs. All were launched on the reliable PSLV, and they continue to anchor national mapping capacity.

Frequently Asked Questions

What is Cartosat?

Cartosat is a series of Indian high-resolution optical earth-observation satellites made by ISRO for cartographic mapping and planning. The series belongs to the Indian Remote Sensing family and was launched on the PSLV.

When was the first Cartosat satellite launched?

The first satellite, Cartosat-1, was launched in May 2005 on a PSLV. It carried two panchromatic cameras that took stereo images for terrain and elevation mapping.

What is the resolution of the Cartosat satellites?

Cartosat-1 had a resolution of roughly two and a half metres, the Cartosat-2 series is finer than one metre, and Cartosat-3 reaches a few tens of centimetres. These values are approximate and depend on the specific satellite and imaging mode.

Which rocket launches the Cartosat satellites?

The Polar Satellite Launch Vehicle (PSLV) launched the Cartosat satellites. The PSLV is ISRO’s workhorse rocket for placing satellites in sun-synchronous polar orbits from Sriharikota.

What are Cartosat images used for?

Cartosat images are used for large-scale mapping, urban and infrastructure planning, cadastral and land record work, terrain modelling and disaster damage assessment. Their fine detail allows buildings, roads and plots to be identified.

Are the Cartosat satellites used for surveillance?

Yes, the higher-resolution Cartosat satellites are widely reported to support strategic and surveillance needs in addition to civilian mapping. Imaging satellites are dual-use, though official sources focus mainly on civilian applications and do not publish details of tasking.

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