Cartosat series

Geography glossary

Topic: Remote Sensing, GIS and GNSS · NCERT: Beyond NCERT

Meaning

The Cartosat series is ISRO's group of Earth observation satellites built mainly for mapping. They take very sharp pictures of the ground from a sun-synchronous polar orbit. Cartosat-1 (2005) took stereo images (two views of one place) to measure the height of the land. Cartosat-3 (2019) can see objects about 25 cm across.

India uses these images for cadastral maps (land-record maps), city planning, height maps of the land and defence. The series is a key step in India's move from early experimental satellites to its own fleet of satellites, each built for one job.

Explanation

Key ideas you need first

  • Earth observation (EO) satellite: a satellite whose sensors (instruments that record energy coming from the earth) collect images of land, water, ice and air.
  • Spatial resolution: the size of the smallest patch of ground that one pixel of the image shows.
  • "25 cm" means one pixel covers a patch only 25 cm × 25 cm.

  • A smaller number means a sharper image.

  • Optical sensing: Cartosat cameras record sunlight that bounces off the earth. So they need daylight and clear skies. They cannot see through cloud.

  • Sun-synchronous polar orbit (SSPO): a near-polar orbit about 500–900 km high.
  • The satellite passes over each place at the same local time on every pass.
  • So the sunlight is the same in every image, and images from different dates are easy to compare.
  • Cartosat, like the rest of India's IRS family, uses this orbit.

Cartosat-1 (2005): stereo pairs for height

  • The problem: a normal satellite image is flat. It shows where things are but not how high the land is.
  • How it works: Cartosat-1 photographed the same place from two different angles. This pair of images is called a stereo pair.
  • It works like our two eyes. Each eye sees from a slightly different angle, and the brain uses the difference to judge depth.

  • Comparing the two images gives the height of each point on the ground.

  • Result: we get a DEM (Digital Elevation Model), a 3D map of land height made on a computer.

  • What DEMs are used for:
  • drawing contour maps (lines joining places of equal height);
  • planning roads and dams, which need the slope and height of the land;
  • mapping watersheds (the area of land that drains into one stream or river).

Cartosat-3 (2019): very fine detail

  • It reaches about 25 cm resolution.
  • At this level you can see single vehicles and the outline of buildings.
  • Why this matters:
  • City planning: planners can map each building, road and open space.
  • Cadastral mapping: land-record maps that show the boundary of each plot of land.
  • Defence: watching sensitive sites in detail.

Where Cartosat fits in India's EO fleet

  • India's path went from experiments to a fleet where each satellite has its own job:
  • Bhaskara-I (1979) and Bhaskara-II (1981): experimental satellites launched on Soviet rockets.
  • IRS-1A (1988): the first satellite of the Indian Remote Sensing (IRS) series.

  • Special-purpose satellites came after that: Resourcesat (crops), Cartosat (maps), Oceansat (ocean) and RISAT (radar).

  • Cartosat is the mapping specialist. Its main strength is sharp detail and land height, not colour or crop health.

  • How sharpness has improved in Indian satellites:
  • IRS-1A's LISS-I: 72.5 m
  • IRS-1C's PAN camera (1995): 5.8 m
  • Cartosat-3 (2019): about 0.25 m (25 cm)

Where it occurs

  • Who runs it: ISRO, as part of India's own fleet of Earth observation satellites. The series began with Cartosat-1 in 2005. Cartosat-3 followed in 2019.
  • Orbit: a sun-synchronous polar orbit, the same type used by Landsat, Sentinel, IRS, RISAT and NISAR. It gives fine detail, but the satellite comes back over the same place only every few days.
  • How it is used in India:
  • Hilly and mountain areas: DEMs from stereo pairs help plan roads and dams and map watersheds where slope matters most.
  • Towns and cities: 25 cm images help map buildings and roads for city planning.
  • Villages and farmland: cadastral (land-record) maps show the boundary of each plot.

  • Borders and defence: detailed images of sensitive areas.

  • Its limit in India: thick cloud covers the country during the south-west monsoon (June–September). An optical satellite like Cartosat sees little then. Radar satellites such as RISAT and NISAR fill this gap.

Don't confuse with

  • Resourcesat: made for crops, land and water. Its AWiFS, LISS-III and LISS-IV cameras record several colour bands to show crop type and health. Cartosat is made for maps and land height.
  • RISAT / EOS-04: a C-band SAR (radar) satellite. It sends out its own microwaves and sees through cloud and at night. Cartosat is optical, so it needs sunlight and clear skies.
  • Oceansat: maps chlorophyll, potential fishing zones and sea-surface winds over the ocean. It is not used for land maps.
  • INSAT-3DS: a geostationary weather satellite about 35,786 km up. It watches clouds all the time but in coarse detail. Cartosat is in a low polar orbit and gives very sharp detail.

Prelims Hooks

  • Cartosat-1 (2005) took stereo pairs (two images from two angles), which are used to make DEMs (3D height maps of the land).
  • Cartosat-3 (2019) has a resolution of about 25 cm. It can show single vehicles and the outline of buildings.
  • Match each satellite to its job: Cartosat → mapping/DEM; Resourcesat → crops; Oceansat → potential fishing zones (PFZ)/chlorophyll; RISAT → C-band SAR. A common trap swaps Cartosat with Resourcesat.
  • Orbit trap: Cartosat is in a sun-synchronous polar orbit, not a geostationary orbit. INSAT-3DS is the geostationary one.
  • Indian sensors from coarse to sharp: LISS-I 72.5 m → LISS-II 36.25 m → LISS-III 23 m → PAN 5.8 m (IRS-1C) → Cartosat-3 ≈ 25 cm.
  • Cartosat is optical, so it is blocked by monsoon cloud. Radar satellites (RISAT, NISAR) are the ones that see through cloud.

Mains Points

  • Better land records and planning (GS-I and GS-III):
  • Cartosat-3's 25 cm images can show the boundary of each plot and building.
  • This supports cadastral mapping (land-record maps), which can cut down land disputes.

  • It also supports city planning for fast-growing towns.

  • Height maps for infrastructure and water (GS-III):

  • Stereo images from Cartosat-1 give DEMs.

  • DEMs guide the route of roads, where dams are built and how watersheds are managed, which matters most in hilly land.

  • The optical limit and the need for radar (GS-III, disasters):

  • Floods and kharif sowing come during the south-west monsoon, when cloud blocks optical satellites like Cartosat.
  • Radar fills this gap. RISAT/EOS-04 uses C-band, and NISAR carries L-band and S-band radar [1].
  • Using Cartosat (sharp detail) together with radar (all-weather view) gives India useful satellite images in every season.

Related concepts

Read more

Sources

  1. 1ISRO — GSLV-F16/NISAR mission page and launch brochureisro.gov.in · tier 1