Megha-Tropiques: follow water and energy in the tropics

Megha-Tropiques was a joint mission of India’s ISRO and France’s CNES, launched on October 12, 2011. Its scientific focus was the movement of water and energy through tropical weather systems. Clouds, water vapor, precipitation and radiation interact in ways that matter beyond a single storm or country. The mission connected repeated measurements with questions about tropical convection — open definition and climate.

Its orbit was inclined about 20 degrees to the equator, concentrating observations on the tropical region. This was a deliberate sampling choice rather than a failure to cover the poles. An orbit can be valuable because it repeatedly samples the region relevant to a scientific problem. Coverage should be evaluated against the question instead of assuming that every mission needs the same global observing pattern.

The mission carried the jointly developed MADRAS microwave imaging radiometer, CNES’s SAPHIR humidity sounder and ScaRaB radiation-budget instrument, and the Italian-procured ROSA radio-occultation payload. These instruments supplied complementary information. Humidity structure, rainfall-related signals and outgoing radiation are connected quantities, but one instrument does not directly measure all of them in the same way.

The collaboration included spacecraft development, instruments, commissioning, ground reception and scientific processing. CNES’s mission account describes its expertise center and reception of some data at Kourou. Such responsibilities are part of the mission, not details that disappear once a satellite launches. An international label becomes meaningful when the actual contributions and interfaces remain visible.

Megha-Tropiques: match sampling to the question

The mission continued beyond its original three-year lifetime, with later extensions supported by useful spacecraft and instrument performance. That does not imply every instrument remained equally capable throughout the mission. Studies using the archive should identify the instrument, acquisition period and product quality appropriate to their question, rather than treating the entire mission duration as one uniform dataset.

ISRO carried out a controlled atmospheric reentry on March 7, 2023, after lowering the orbit through a planned sequence of maneuvers. The spacecraft’s disposal and the survival of its scientific record are different outcomes: preserved observations can still be analyzed after the vehicle is gone. For a fictional comparison of tropical storms, document the sampling and processing of the archived observations before attributing differences to climate or weather.