The Oceansat Satellites Explained

Oceansat is India’s series of ocean-observation satellites, built by the Indian Space Research Organisation (ISRO) within the Indian Remote Sensing (IRS) programme to measure ocean colour, sea-surface winds and related marine conditions from sun-synchronous orbit. The series has so far comprised three missions: Oceansat-1 (also called IRS-P4, launched in 1999), Oceansat-2 (launched in 2009) and Oceansat-3 (also called EOS-06, launched in 2022), all carried into orbit by the Polar Satellite Launch Vehicle (PSLV).

The data from these satellites feeds fisheries advisories, cyclone and monsoon forecasting, coastal studies and the wider blue economy. This explainer describes what each Oceansat mission carried, how the instruments work, and why ocean-colour and wind measurements matter for a country with a coastline of roughly 7,500 kilometres. Last updated: 16 October 2026.

Key Takeaways

• Oceansat is a series of three Indian ocean-observation satellites: Oceansat-1 (IRS-P4) launched in 1999, Oceansat-2 launched in 2009, and Oceansat-3 (EOS-06) launched in 2022.
• The Ocean Colour Monitor (OCM) on the Oceansat satellites measures the colour of seawater to estimate chlorophyll and phytoplankton concentration, which indicates where fish are likely to gather.
• A Ku-band scatterometer on Oceansat-2 and Oceansat-3 measures ocean-surface wind speed and direction, which supports cyclone tracking and weather forecasting.
• Oceansat data underpins the Potential Fishing Zone (PFZ) advisories issued by the Indian National Centre for Ocean Information Services (INCOIS) to fishers along the Indian coast.
• All three Oceansat satellites were launched by ISRO’s Polar Satellite Launch Vehicle (PSLV) into sun-synchronous orbit from the Satish Dhawan Space Centre at Sriharikota.
• Oceansat-3 improved on earlier missions by adding more ocean-colour bands, a sea-surface temperature monitor and a scatterometer in a single satellite.

What is Oceansat?

Oceansat is the name of ISRO’s dedicated ocean-observation satellite series, designed to study the colour, temperature and wind patterns of the seas around India and the wider global ocean. The satellites belong to the Indian Remote Sensing (IRS) family, which also includes the Cartosat, Resourcesat and RISAT series that look at land, cities, crops and water from space.

Unlike general-purpose Earth-observation satellites, the Oceansat spacecraft carry instruments tuned to the sea. Seawater absorbs and scatters sunlight in ways that depend on what is dissolved or suspended in it, and the ocean surface roughens predictably as wind blows across it. Oceansat instruments exploit both effects to turn light and radar signals into maps of biological activity and wind.

The series is operated for practical purposes. Its main output is not images for display but measurements that other agencies convert into forecasts, advisories and long-term climate records.

Why did India build dedicated ocean satellites?

India built dedicated ocean satellites because its long coastline, large exclusive economic zone, monsoon-driven economy and vulnerability to tropical cyclones all depend on knowing what the surrounding seas are doing. A coastline of roughly 7,500 kilometres, together with millions of people who depend on marine fishing, makes timely ocean information a public-service need rather than a scientific luxury.

Earlier Indian satellites had carried some ocean-related payloads, but ISRO’s Oceansat programme was the first to place a focused ocean-colour sensor in orbit for operational use. The aim was to reduce the time fishers spend searching for productive waters, to improve the warning of storms formed over the Arabian Sea and the Bay of Bengal, and to support scientific work on marine productivity and climate.

Oceans also act as the main source of moisture and heat for the Indian monsoon. Wind and temperature observations over the sea are therefore inputs to forecasts that affect agriculture, water management and disaster preparedness well beyond the coast.

What are the Oceansat missions and when were they launched?

There are three Oceansat missions so far: Oceansat-1 (IRS-P4) in 1999, Oceansat-2 in 2009 and Oceansat-3 (EOS-06) in 2022, each launched by a PSLV from Sriharikota. The table below compares them.

Figures such as resolution, swath and altitude are approximate and vary slightly between published ISRO sources.

What did Oceansat-1 (IRS-P4) do?

Oceansat-1, also known as IRS-P4, was India’s first dedicated ocean-observation satellite and was launched by a PSLV on 26 May 1999. It carried two main instruments: the Ocean Colour Monitor (OCM) and the Multi-frequency Scanning Microwave Radiometer (MSMR).

The OCM was an eight-band camera working in visible and near-infrared wavelengths, with a resolution of around 360 metres and a swath of well over a thousand kilometres. It allowed scientists to estimate chlorophyll concentration, suspended sediment and certain aerosols over the sea. The MSMR measured microwave emission from the ocean surface to derive quantities such as sea-surface temperature, wind speed and water vapour, although at coarser resolution.

Oceansat-1 operated for a number of years, demonstrating that India could produce its own ocean-colour data. It laid the technical foundation, and the user community, for the follow-on missions.

What did Oceansat-2 add?

Oceansat-2 added a Ku-band pencil-beam scatterometer to the Ocean Colour Monitor, giving India an operational source of ocean-surface wind vectors for the first time. The satellite was launched by a PSLV on 23 September 2009, together with several small foreign nanosatellites.

Oceansat-2 carried three instruments:

• Ocean Colour Monitor (OCM): an eight-band visible and near-infrared sensor, continuing the work of Oceansat-1 with a resolution of around 360 metres.
• Ku-band scatterometer: a radar instrument that measures how the sea surface scatters microwave pulses, from which wind speed and direction are derived.
• Radio Occultation Sounder for Atmosphere (ROSA): a payload developed with the Italian Space Agency that studies the temperature and humidity structure of the atmosphere by analysing navigation-satellite signals.

The satellite served well past its planned design life and became a regular data source for weather agencies and fisheries advisories. Its scatterometer data were also assimilated into numerical weather prediction systems in India and abroad.

What is Oceansat-3 (EOS-06) and what does it carry?

Oceansat-3, also designated EOS-06, is the third and most advanced Oceansat satellite, launched by PSLV-C54 on 26 November 2022 into a sun-synchronous orbit of around 740 kilometres. It is part of ISRO’s Earth Observation Satellite (EOS) naming scheme, which replaced older IRS labels for newer missions.

The satellite carries four principal payloads:

• OCM-3: a third-generation Ocean Colour Monitor with around 13 spectral bands, a resolution of roughly 240 metres and a wider swath than before, giving finer information on phytoplankton and water quality.
• Sea Surface Temperature Monitor (SSTM): a thermal-infrared sensor that measures sea-surface temperature, a key variable for fish distribution, cyclone intensification and climate studies.
• Ku-band scatterometer (SCAT-3): a wind-vector instrument continuing the Oceansat-2 capability.
• ARGOS payload: a data-collection and location system developed with French partners, used for tracking ocean buoys and animals and collecting environmental data.

On the same PSLV flight, ISRO also placed several small satellites in orbit for domestic and international customers, which is a common practice for PSLV missions.

What is next for the Oceansat series?

ISRO has indicated plans for follow-on ocean-observation missions that continue and extend the Oceansat measurements, though schedules and exact configurations should be checked against current ISRO announcements. The aim of such missions is to keep long, unbroken data records of chlorophyll, sea-surface temperature and winds, which are valuable precisely because they run for decades.

Continuity matters in ocean science. A gap between satellites makes it harder to compare one decade with the next and to detect real climate trends. Newer sensors with more spectral bands and better resolution also open possibilities in areas such as harmful-algal-bloom detection and finer coastal monitoring.

How does the Ocean Colour Monitor work?

The Ocean Colour Monitor works by measuring sunlight reflected from the upper layer of the sea in several narrow wavelength bands and converting those measurements into estimates of chlorophyll, sediment and dissolved material. Clear, nutrient-poor water appears deep blue, while water rich in phytoplankton absorbs blue light and reflects more green, shifting the observed colour.

Phytoplankton are microscopic, plant-like organisms that form the base of the marine food chain. Because they contain chlorophyll, their abundance can be estimated from space. Where phytoplankton is abundant, zooplankton and small fish tend to follow, and larger commercial fish gather to feed on them.

Why are several bands needed?

Several bands are needed because the signal that reaches the satellite is mostly atmospheric haze, with only a small fraction coming from the water itself. Using bands in the near-infrared allows the atmospheric contribution to be estimated and removed, leaving the ocean signal. More bands, as on Oceansat-3, help separate chlorophyll from suspended sediment and coloured dissolved matter, especially in coastal waters.

What are the limits of ocean-colour sensing?

Ocean-colour sensing cannot see through cloud, and it works only in daylight. During the southwest monsoon, thick cloud over the Arabian Sea and Bay of Bengal limits optical observations, which is why combining several days of data and other sensors is important.

How does the Ku-band scatterometer measure ocean winds?

The Ku-band scatterometer measures ocean winds by sending microwave pulses to the sea surface and recording how strongly they are scattered back by small wind-generated waves. Rougher seas return stronger signals, and viewing the same patch of ocean from different angles allows both wind speed and direction to be inferred.

Radar can operate day and night and can see through most clouds, so the scatterometer complements the optical Ocean Colour Monitor. Its output, called a wind vector, is a map of how fast and in what direction surface winds are blowing across swaths hundreds of kilometres wide.

Where are the wind data used?

Wind-vector data are used to locate and track the centres of tropical cyclones, to estimate their intensity, to initialise weather models, and to study the onset and progress of the monsoon. Forecasters at the India Meteorological Department (IMD) and the National Centre for Medium Range Weather Forecasting (NCMRWF) use scatterometer winds among many inputs. ISRO has also flown a separate scatterometer satellite, SCATSAT-1, launched by PSLV in 2016, to continue this class of observations after Oceansat-2.

How does Oceansat help fishers through Potential Fishing Zone advisories?

Oceansat helps fishers by supplying chlorophyll and sea-surface temperature information that is converted into Potential Fishing Zone (PFZ) advisories, which tell them where fish are most likely to be concentrated. The advisories are prepared and issued by the Indian National Centre for Ocean Information Services (INCOIS) in Hyderabad, an institution of the Ministry of Earth Sciences.

The method combines chlorophyll maps with sea-surface temperature data to find fronts and eddies, where cold, nutrient-rich water meets warmer water and marine life concentrates. These locations are then translated into advisories giving the position of likely fishing areas and their distance and direction from the coast.

Advisories are distributed in regional languages through SMS, radio, television, display boards at fishing harbours, mobile applications and community networks. Fishers who use the advisories can spend less time and fuel on searching, which matters because fuel is among the largest costs of a fishing trip. The reliability of any advisory depends on cloud-free data and on the fishing conditions that day, so the service is a decision aid and not a guarantee of catch.

What are the other applications of Oceansat data?

Beyond fisheries, Oceansat data are applied in cyclone and monsoon prediction, coastal and marine studies, climate research and the blue economy. The following areas are the most prominent.

• Cyclone and storm forecasting: wind vectors from the scatterometer help forecasters locate cyclone centres and wind fields over the Bay of Bengal and the Arabian Sea.
• Monsoon studies: ocean winds and sea-surface temperature influence the strength and timing of the monsoon, so these measurements improve seasonal and short-term forecasts.
• Coastal water quality: ocean-colour data help detect algal blooms, river plumes, sediment and certain kinds of pollution along the coast.
• Marine ecosystems and carbon cycle: long records of chlorophyll show seasonal and year-to-year changes in marine productivity, and help estimate how much carbon the oceans absorb.
• Coral reefs, mangroves and coastal zones: sensors contribute to mapping and monitoring sensitive coastal habitats, usually combined with higher-resolution land imagery.
• Shipping and offshore activity: wind and wave-related information supports route planning and offshore operations.

These uses fit within India’s broader blue-economy goals, which cover sustainable fisheries, shipping, coastal tourism, offshore energy and marine biotechnology.

Who processes and distributes Oceansat data?

Oceansat data are received, processed and distributed by the National Remote Sensing Centre (NRSC) of ISRO in Hyderabad, while INCOIS and other agencies convert the data into services. NRSC operates the ground stations that downlink the satellite data and produces standard products, which are made available to registered users through ISRO’s data portals.

INCOIS handles ocean-state and fishing advisories, while the India Meteorological Department uses the wind products for forecasting. Universities and research institutions, including the National Institute of Oceanography and the Space Applications Centre (SAC) in Ahmedabad, use the data for scientific studies. SAC also contributed to the design and development of the Oceansat sensors.

How does PSLV launch the Oceansat satellites?

The PSLV launches the Oceansat satellites from the Satish Dhawan Space Centre at Sriharikota in Andhra Pradesh, placing them into near-polar, sun-synchronous orbits. A sun-synchronous orbit passes over any given latitude at nearly the same local solar time on each pass, which gives consistent lighting for optical sensors such as the Ocean Colour Monitor.

The PSLV is a four-stage rocket that alternates solid and liquid propulsion stages, and it has been the standard vehicle for India’s remote-sensing satellites. Its reliability and its ability to carry additional small satellites as secondary payloads have made it a regular choice for Earth-observation launches. Each Oceansat mission has flown on the PSLV, and the satellites have orbited the Earth many times a day, repeating coverage of the same ocean areas every few days.

Bottom Line

Oceansat is India’s long-running family of ocean satellites, spanning Oceansat-1 in 1999, Oceansat-2 in 2009 and Oceansat-3 (EOS-06) in 2022. By measuring ocean colour, sea-surface temperature and wind, the series supports fishing advisories, cyclone and monsoon forecasts, coastal studies and the blue economy.

Frequently Asked Questions

What is Oceansat?

Oceansat is a series of Indian ocean-observation satellites built by ISRO under the Indian Remote Sensing programme. The series includes Oceansat-1 (IRS-P4), Oceansat-2 and Oceansat-3 (EOS-06), which carry instruments to measure ocean colour, sea-surface winds and temperature. Their data support fisheries, weather forecasting and marine research.

When were the Oceansat satellites launched?

Oceansat-1 was launched in May 1999, Oceansat-2 in September 2009 and Oceansat-3 (EOS-06) in November 2022. All three were launched by ISRO’s PSLV from Sriharikota. Each was placed in a sun-synchronous polar orbit at an altitude of roughly 720 to 740 kilometres.

What does the Ocean Colour Monitor do?

The Ocean Colour Monitor measures the colour of seawater to estimate chlorophyll and phytoplankton concentration. Because phytoplankton forms the base of the marine food chain, these maps help identify productive waters where fish are likely to gather. The data also help track sediment, algal blooms and coastal water quality.

How does Oceansat help predict cyclones?

Oceansat helps predict cyclones mainly through its Ku-band scatterometer, which measures ocean-surface wind speed and direction. Forecasters use these wind vectors to locate a cyclone’s centre and understand its wind field. The data, along with sea-surface temperature observations, feed into weather forecasting models.

What are Potential Fishing Zone advisories?

Potential Fishing Zone (PFZ) advisories are guidance messages that tell fishers where fish are likely to be concentrated. INCOIS prepares them using Oceansat-derived chlorophyll data along with sea-surface temperature information. They are shared in regional languages through SMS, radio, television, mobile apps and harbour display boards.

Which agencies use Oceansat data?

Oceansat data are used by ISRO’s National Remote Sensing Centre, the Indian National Centre for Ocean Information Services (INCOIS), the India Meteorological Department and several research institutions. They are applied in fisheries advisories, weather and cyclone forecasting, and marine and coastal studies. Fisheries departments and coastal communities benefit through the advisories built from the data.

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