TRISHNA: The satellite that measures Earth’s thirst

Picture a farmer standing between two fields that look equally green. One holds enough water to carry the crop through the season; the other is quietly beginning to parch. No human eye can tell them apart. Within about a year and a half, a satellite built by Indian and French hands will be able to. That satellite is TRISHNA, short for Thermal Infra-Red Imaging Satellite for High-resolution Natural Resource Assessment.

The satellite will be ready for launch in the next 12 to 16 months. It will ride into orbit aboard India's own Polar Satellite Launch Vehicle, the PSLV.

This was recently announced by Jasvinder Singh Khoral, Director (Projects) at the U.R. Rao Satellite Centre (URSC), at a workshop.

The road to this moment has been long. Khoral noted that the project has been under discussion and planning for nearly ten years, and only now are those plans turning into hardware. Behind that decade lie countless reviews, recalculations and late nights, along with a shared conviction between two nations that water is the resource most worth watching from above.

“The science rests on a simple truth: every object gives off invisible heat radiation according to its temperature. TRISHNA's thermal infrared instrument, developed by CNES, the French space agency, will sense this heat from orbit. Dry, stressed farmland warms faster than land holding enough moisture, so a temperature map quietly becomes a map of thirst, and a guide for farmers deciding where irrigation is needed most. Alongside it sits a second instrument built by ISRO that observes in visible light, near infrared and shortwave infrared. Visible light is the ordinary sunlight our eyes use; it shows green forests, blue water, brown soil and the patchwork of fields. Shortwave infrared lies beyond human sight but reveals how much moisture plants and soil actually hold, which is precisely how those two identical-looking fields will be told apart,” explained space analyst Girish Linganna.

Explaining further, this expert says that together, these readings let scientists measure not only surface temperature but also emissivity, the efficiency with which land, water and vegetation release heat. In simpler words, the satellite will show how the land holds or loses warmth. The mission will track how plants grow and fare, and how sunlight and heat act upon the ground. Because TRISHNA photographs small patches of land in fine detail and returns to the same spots frequently, it will reveal how much of the Sun's energy the ground soaks up, how much it gives back, and how that balance shifts from one region to another and across the world.

According to Nagalakshmi A.M., Project Director of TRISHNA, the mission will help in managing water more wisely. Knowing water availability, soil moisture, crop condition and water use will make planning and managing this precious resource far easier. She also confirmed that TRISHNA will follow an open data policy. Its findings will be freely available to researchers and users anywhere on the planet, without needless restrictions or delays.

“The work is shared with care. URSC is building the satellite's body, the frame that carries the instruments and keeps them powered, connected and steered. The centre is also preparing the instruments India is responsible for, while CNES supplies the rest. Once data begins flowing down, scientists from both countries will process and study it together,” added Linganna.

TRISHNA is the third chapter in an Indo-French partnership that has repeatedly outlived its own promises. Megha-Tropiques, launched on October 12, 2011, studied rainfall, clouds, atmospheric moisture and weather changes across the tropics.

Designed for three years, it kept delivering for more than ten, until 2021, before being brought back into the atmosphere and safely disposed of over the Pacific Ocean on March 7, 2023. SARAL, the Satellite with ARGOS and ALTIKA, followed on February 25, 2013, to study sea levels, ocean conditions and changes in the Earth's climate, while also helping scientists understand ocean currents and monitor rivers, lakes and ice-covered regions. Built to last five years, it has now worked for more than 13 and, according to the French space agency, remains operational.

For a country where the monsoon decides harvests, incomes and the mood of entire villages, a satellite that can read the land's thirst before anyone on the ground notices is a major breakthrough.