Thermal infrared remote sensing can transform India's approach to water and food security. Discuss with reference to the ISRO-CNES TRISHNA mission.

Thermal infrared (TIR) remote sensing measures the heat given off by land and water. From this it maps land surface temperature and evapotranspiration, which is the water crops actually use. The ISRO-CNES TRISHNA mission is expected to launch within the next 12–16 months [4]. It can help India move from managing water supply to measuring water use, field by field.

TRISHNA: what it brings

• CNES provides a 4-channel TIR imager and ISRO a 7-band VNIR-SWIR instrument. The satellite will fly in a 761 km sun-synchronous orbit [1].
• It will have 57 m resolution over land, which is detailed enough to see individual fields [1].
• It is the third Indo-French satellite, after Megha-Tropiques (2011) and SARAL (2013) [2].

Transforming water security

• Water budgeting: Evapotranspiration maps measure water use and water stress, so water can be accounted for at the basin level [1].
• Drought monitoring: Satellite tracking of evapotranspiration and surface heat shows water stress early. This strengthens drought warning [1].
• Water quality: It can detect pollution and groundwater seeping into the sea in coastal and inland waters [1].
• Cryosphere: Tracking snowmelt improves models of river flow from the Himalayas [1].

Transforming food security

• Precision irrigation: Estimates of irrigation water use and water-saving advice support the aim of "more crop per drop" [1].
• Crop water productivity: Data on crop water use and micro-watersheds helps plan rain-fed farming [1].
• Global linkages: It feeds GEOGLAM crop monitoring and reporting on the SDGs [1].

Challenges

• Schedule slippage: CNES's mission page still lists a 2026 launch [3]. The target has now moved to 2027–28 [4].
• Cloud cover: Thermal sensors cannot see through clouds. This limits what they can observe during the kharif (monsoon) season.
• Last-mile use: The benefits depend on open access to data and on state agriculture and irrigation departments being able to use it.

By pairing thermal and optical sensing, TRISHNA makes the water used by crops visible, from single fields to whole basins. Its benefits can be secured by adding its data to Per Drop More Crop under PMKSY, drought manuals and state water plans, and by training field agencies to use it. Done well, it can move India towards data-driven water management that advances SDG 2 (Zero Hunger) and SDG 6 (Clean Water).