TRISHNA (Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment)
Albedo and reflectance
Cloud type, amount and cloud top temperature
Planned for launch in 2025, Thermal InfraRed Imaging Satellite for High-resolution Natural resource Assessment (TRISHNA) is a joint development by the French Space Agency (CNES) and Indian Space Research Organization (ISRO). The satellite will join the Franco-Indian fleet for use in climate monitoring and operational applications.
|Launch date||Dec 2024|
|End of life date||Dec 2029|
|Measurement domain||Atmosphere, Land, Snow & Ice|
|Measurement category||Albedo and reflectance, Cloud type, amount and cloud top temperature, Sea ice cover, edge and thickness, Snow cover, edge and depth, Surface temperature (land), Vegetation|
|Instruments||SWIR, TIR, VNIR|
|Instrument type||Imaging multi-spectral radiometers (vis/IR)|
|CEOS EO Handbook||See TRISHNA (Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment) summary|
TRISHNA features two sensors, a Thermal InfraRed (TIR) instrument and a Visible and Near Infrared (VNIR)/Short Wave InfraRed (SWIR) sensor (VSWIR). TIR features four thermal bands to measure top-of atmosphere radiances, brightness temperatures, surface radiance, temperature, and emissivity. Variables associated with the energy budget at the soil-plant-atmosphere interface are also measured including net radiation, evapotranspiration, and water stress index. TIR will have a significant impact on studies involving climate change where sea and land surface temperatures are key variables.
VSWIR will complement TIR to provide observations in six VNIR/SWIR bands. This will deliver crucial information on water use, soil pollution, coastal and inland water monitoring, urban microclimate monitoring, volcanic monitoring, geothermal exploration, vegetation and land coverage, cryosphere monitoring, and information on the atmosphere and clouds.
Improving upon current TIR missions, TRISHNA will image the Earth every three days, at 57 m resolution, observing a wide temperature range, from about -20°C to +30°C, with a precision of 0.3°C.
TRISHNA will operate in a sun-synchronous orbit at an altitude of 761 km, with a Local Time of Descending Node (LTDN) of 1300 hours.
Space and Hardware Components
Built by ISRO, the satellite bus will be developed from an existing IRS-1k model, adapted to the requirements of the TRISHNA mission. The bus will accommodate the instrument payload and supply propulsion, power (via 2kW solar panels), and orientation to control the satellite’s trajectory. It features a mass of 770 kg, with a design life of five years.
Telemetry data is relayed to the ground via an X-band link at 640 Mbps.
TRISHNA (Thermal InfraRed Imaging Satellite for High resolution Natural resource Assessment)
The French Space Agency CNES (Centre National d'Etudes Spatiales) has recently signed a contract with Airbus Defence and Space for the development and manufacture of the thermal infrared instrument for the TRISHNA satellite mission. The spacecraft will be the latest satellite in the joint Franco-Indian satellite fleet dedicated to climate monitoring and operational applications. CNES and ISRO (Indian Space Research Organization) are partnering on the development of an infrared observation system with high thermal resolution and high revisit capability including a satellite and associated ground segment. 1)2)
TRISHNA observations will enhance our understanding of the water cycle and improve management of the planet’s precious water resources, to better define the impacts of climate change, especially at local levels.
The mission is an international partnership, where ISRO will provide the platform, the visible and short wave infrared instrument, and will be the prime contractor for the satellite. CNES will be co-responsible for the mission and will provide the thermal infrared instrument, to be developed by Airbus. The ground segment is shared between both countries.
For this mission, Airbus is leveraging the latest innovations and synergies from other programs (IASI-NG, CO3D) to offer an affordable high performance instrument, with the aim of encouraging development of a commercial market.
Measuring surface temperatures provides information on hydric stress, a lack of water, and its impact on the vegetative cycle. This monitoring of water and energy cycles is one of the main objectives of the mission, to be applied particularly in agriculture and hydrology. This mission will also serve numerous other applications: surveillance of continental and coastal waters, follow up of urban heat traps, risk monitoring (fire detection and volcanic activity), study of the cryosphere (glaciers, frozen lakes) and radiation budget assessment.
TRISHNA represents a significant step forward, both in terms of resolution and refresh rate, compared with existing missions, improving research opportunities and enabling further development of applications. TRISHNA will image the Earth every three days, at 50 m resolution, observing a wide temperature range, from about -20°C to +30°C, with high precision (0.3°C). This is a significant improvement on existing missions whose spatial resolution is on the order of 1 km.
Jean-Marc Nasr, Head of Space Systems at Airbus said: “Thanks to ambitious science missions like TRISHNA, our industry has reached a technological maturity that opens up a new era of commercial observation of the Earth and all related applications. France’s world-leading expertise in the Earth observation export market, combined with the unmatched efficiency and ambition of the Indian Space industry is going to bring thermal infrared imagery to a new level. This will enable breakthrough applications in agriculture, urban and coastal zone management, meteorology, climate science and many commercial applications.”
TRISHNA mission of ISRO and CNES 3)
Introduction: The monitoring of the water cycle at the Earth’s surface supports the assessment of climate change processes, as well as a number of management applications (e.g. agriculture, soil and water quality assessment, irrigation and water resource management). This monitoring requires surface temperature measurements at local scale, and supporting this is the goal of the TRISHNA mission. TRISHNA is planned for launch in 2025, and carries both a thermal infrared instrument and a visible and short-wave infrared, with a five-year mission planned.
Scientific objectives include:
- ecosystem stress and water use (better management of water resources);
- coastal and inland waters (water quality, fish resource, sea ice);
- urban microclimates monitoring (characterization of urban heat island);
- solid earth (detection of thermal anomalies); and,
- cryosphere (monitoring of snow and ice), atmosphere (water content, cloud characterization).
The scientific community involved in climate change studies, for whom sea and land surface temperatures are key variables, are expecting to make significant progress thanks to TRISHNA. In addition, the mission will deliver innovative products for water resource management that can inform decision-making at all levels, from farmer (water stress status, irrigation) to institutional (land-use management and policy, climate change impact mitigation).
TRISHNA will also contribute to the preparation of future Copernicus services, by pushing the development of new instrumental techniques, and through the preparation and validation of the data processing chains, the products and the applications.
Ecosystem stress and water use (design driver): Land Surface Temperature (LST) is a key information to estimate evapotranspiration (ET), a crucial component of the water cycle. For agriculture, which represents about 70% of the water consumption at global scale, applications to stress detection and irrigation optimization techniques are expected for a better management of water resources, improved crop production forecast and food security assessment. As CO2 and water transfers in plants are tightly coupled, and as water is the vector of many dissolved materials within the soil, LST can help to monitor biogeochemical cycles with applications to water quality and soil pollution monitoring. Dealing with hydrology, improved estimation of ET at watershed scale should also facilitate the closure of water budgets and estimation of infiltration, runoff, river flow, etc. Other applications will be found in the field of ecology (e.g. mapping of microclimates, permafrost melting).
Coastal and inland waters (design driver): A better assessment of the sub-mesoscale activity in relation with coastal ecosystems productivity and of gas fluxes (CO2, CH4) at the air-sea interfaces is expected from high spatiotemporal resolution Sea Surface Temperature (SST). The availability of such SST data opens the way to a large number of applications: water quality, algae blooms, fish resource, fresh water resurgences, water discharges and storm surges (e.g. pollutants, thermal plumes) among others. Moreover, the surface temperature of lakes has been defined as an essential climate variable (ECV) by GCOS (Global Climate Observing System). The study of sea ice (extent, growth/decay of ice, feedback with climate) will also benefit from TRISHNA data.
Urban microclimate monitoring: More and more efforts are devoted to the characterization of urban heat islands (UHI) and to their possible mitigation or heat action plans for comfort of inhabitants (by ’greening’ of the city, urban planning or control of air conditioning energy consumption for instance). Improved evaporation estimations should also provide better inputs for urban and peri-urban hydrology studies.
Solid Earth: TRISHNA should improve the detection of thermal anomalies with various applications: peat or coal fires mapping, geothermal exploration, possibly earthquake precursors, among others. It could also contribute to the monitoring of volcanic activity through the early detection of lava hot spots.
Cryosphere: The feedbacks between climate and melting processes make the monitoring of snow and ice critical in polar regions. It is also particularly important for glaciers and glacial high altitude lakes in mountainous regions as the snow and glacier melt runoff represents a perennial source of water for river basins. This is crucial for India which is partly dependent on Himalayan cryosphere.
Atmosphere: Different information on atmosphere (precipitable water content) and clouds (type, height) can be derived from thermal infrared data for improving Earth radiative budgets.
The TRISHNA project is managed by a joint Indian-French project team, with roles outlined in Figure 3.
Airbus Defence and Space has entered an agreement with the French Space Agency (CNES) to develop an instrument for the thermal infrared imaging satellite for high-resolution natural resource assessment (TRISHNA) system. Under this contract, Airbus will be responsible for the production of the thermal infrared instrument for the TRISHNA satellite.
Built by ISRO, the satellite bus will be developed from an existing IRS-1k model, adapted to the requirements of the TRISHNA mission. The bus will accommodate the instrument payload and supply propulsion, power (via 2kW solar panels) and orientation to control the satellite’s trajectory. It features a mass of 770 kg, with onboard storage of 1.4 Terra bits of data. Telemetry data is related to ground via an X-band link at 640 Mbps.
Launch: The satellite will be launched from Sriharikota by an Indian Polar Satellite Launch Vehicle (PSLV). It will be controlled from the mission control centre in Bangalore. It is currently set for launch in 2025.
Orbit: Trishna’s orbit has a cycle of 8 days: in other words, every 8 days, Trishna is exactly at the same place, above the same pixel. But thanks to the very large field of view of its instruments, Trishna can observe each point on the earth at least three times per 8 day cycle. As a result, the revisit period is always better than three days everywhere on Earth, but the observations are made with different viewing angles. But the chosen orbit allows Trishna to make observations with constant viewing angles every 8 days.
5 years (+2)
VSWIR instrument + TIR instrument
Global, day (VSWIR+TIR) and night (TIR only)
Polar phased sun-synchronous
8 days (same view angle)
3 passes every 8 days (different view angles)
Overpass time at equator
13 hours (on descending node)
Pixel size (land and coastal)
57 m (nadir) to 90 m
Pixel size (deep ocean)
12 hours on selected products (L2)
Free and open (specific agreements may be required)
- Mid-2025: transition to operational phase.
- Beginning of 2025: planned launch.
- The satellite will be launched from Sriharikota by an Indian Polar Satellite Launch Vehicle (PSLV). It will be controlled from the mission control centre in Bangalore. It is currently set for launch in 2025.
- June 2024: delivery of instrument to India.
- July 2022: detailed design review.
- June 2021: Instrument Preliminary Definition Review:.
- 4 June 2020: Start of TIR instrument development by Airbus.
- For this mission, Airbus is leveraging the latest innovations from other programs (IASI-NG, CO3) to offer an affordable high performance instrument, with the aim of encouraging development of a commercial market.
Trishna’s Thermal InfraRed (TIR) telescope, developed by CNES, will be supplemented by an optical Visible and Near Infrared (VNIR)/Short Wave InfraRed (SWIR) sensor (VSWIR) supplied by ISRO. Observing simultaneously in the visible and thermal portions of the spectrum will make it easier to juxtapose data for analysis in several fields of investigation including ecosystem water stress and water resource management, hydrology of coastal strips and land surfaces, urban , heat islands, the cryosphere and atmosphere.
TIR Instrument: A rotating scan mirror allows the telescope to view a 68 degrees-wide nadir cross-track swath as well as – for calibration – an internal blackbody and cold-space view every 5 seconds. The optical signal is focused by a telescope onto the 60 K focal plane containing a mercury-cadmium-telluride infrared detector array. Spectral filters on the focal plane define 4 spectral bands in the 8-12 µm range.
Three-mirror anastigmat telescope
Number of spectral bands
TIR1 – TIR2 – TIR3 – TIR4
Specified central wavelengths
8.65 µm – 9.0 µm – 10.6 µm – 11.6 µm
Specified FWHM per band
0.35 µm – 0.35 µm – 0.7 µm – 1.0 µm
0.7 K at 300 K
Radiometric typical precision (NedT)
0.15 K at 300 K
250 K – 400 K
Focal plane temperature
1 blackbody + 1 cold space view
The VSWIR instrument is made of 6 small cameras, 3 for the VNIR bands, and 3 for the SWIR bands. The 3 cameras per wavelength range are necessary to cover the whole field of view. Each camera contains all the bands of the selected range.
Number of spectral bands
Blue – Green – Red – NIR – Cirrus - SWIR
Specified central wavelengths (nm)
485 – 555 – 670 – 860 – 1380 - 1610
Specified FWHM (Full Width Half Maximum) per band (nm)
70 – 70 – 60 – 40 – 30 - 100
Number of optical heads
3 (VNIR) + 3 (SWIR)
FOV per EOM
f/5 (VNIR) – f/4.5 (SWIR)
Wavelength Centre (nm)
Required SNR @ Ltyp
Detection of low clouds
Coastal, sediments, snow
Vegetation (LAI, fCOVER, NDVI, ...)
Vegetation (LAI, fCOVER, NDVI, ...)
Detection of thin cirrus clouds
AOD, snow/cloud discrimination, vgt stress, burnt areas
TRISHNA products: A free and open data policy intends to maximise the use of the data, in order to enhance scientific knowledge and maximise scientific benefit, but also with the objective of promoting the development of applications for societal benefit. Product levels 1, 2 and 3 will be available to the users.
Level 1 products (top-of-atmosphere values, together with a coarse cloud mask, resampled onto a cartographic grid) are top-of-atmosphere reflectances (visible and SWIR) and top-of-atmosphere radiances (thermal infrared wavelengths) and brightness temperatures.
Level 2a products are single-date radiative variables that may be processed differently according to their nature: the products include scene classification and atmospheric variables. Data delivered are surface reflectance (in reflective domain) after atmospheric correction, albedo, surface radiance in thermal infrared after atmospheric correction, temperature and emissivity.
Level 2b are biophysical variables computed using level 2a variables together with exogenous sources of information (models). Typical level 2b variables for ecosystem stress are LAI (leaf area index), FVC (fractional vegetation cover), FAPAR (Fraction of Absorbed Photosynthetically Active Radiation). Variables associated with the energy budget at soil-plant-atmosphere interface are also delivered: net radiation, evapotranspiration, water stress index.
Level 3 are temporal syntheses (decadal, monthly) of level 2 variables.
A third instrument is to be flown onboard TRISHA, a Millimetre Wave Atmospheric Temperature & Humidity Sounder (MATHS). MATHS, built by ISRO, is not part of the Trishna mission but will be taking advantage of a ride share on the satellite.
Science data will be downlinked to the two mission centres, one in India, one in France. Technical evaluation of thermal infrared data will be performed by the French team and evaluation of SWIR data by the Indian team. All of the mission’s science data will be accessible for analysis and distribution by the two partners.
Each of the Indian and French payload ground segments can process and distribute all types of TRISHNA products: indeed, the data processing uses the mutual enrichment resulting from the gathering of reflective and thermal data acquired at the same time by both instruments. Hence, the Indian and French payload data processing chains are functionally identical.
1) ”Airbus will support France and India to monitor climate change with TRISHNA,” Airbus, 20 April 2020, URL: https://web.archive.org/web/20210509133556/https://www.airbus.com/newsroom/press-releases/en/2020/04/airbus-will-support-france-and-india-to-monitor-climate-change-with-trishna.html
2) J.-P. Lagouarde,B. K. Bhattacharya, P. Crébassol, P. Gamet, S. S. Babu, G. Boulet, X. Briottet, K. M. Buddhiraju, S. Cherchali, I. Dadou, G. Dedieu, M. Gouhier, O. Hagolle, M. Irvine, F. Jacob, A. Kumar, K. K. Kumar , B. Laignel, K. Mallick, C. S. Murthy, A. Olioso, C. Ottlé, M. R. Pandya, P. V. Raju, J.-L. Roujean, M. Sekhar, M. V. Shukla, S. K. Singh, J. Sobrino, R. Ramakrishnan, ”The Indian-French TRISHNA Mission: Earth Observation in the thermal infrared with high spatio-temporal resolution,” IGARSS 2018 (IEEE International Geoscience and Remote Sensing Symposium), Valencia, Spain, 22-27 July 2018, https://doi.org/10.1109/IGARSS.2018.8518720
3) Philippe Gamet, Jean-Pierre Lagouarde, Jean-Louis Roujean, Olivier Hagolle, ”TRISHNA : Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment,” CESBIO, URL: https://labo.obs-mip.fr/multitemp/trishna/
4) “TRISHNA”, CNES, 12 June 2020, URL: https://trishna.cnes.fr/en/trishna-0
5) “TRISHNA Days”, March 2022, URL: https://www.trishnadays.com/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).