Megha Tropiques

Megha-Tropiques is an Indo-French collaborative satellite mission designed to study the water and energy dynamics of the tropical atmosphere, particularly focusing on weather systems, monsoon processes, and climate variability. Launched in October 2011, the satellite represents a significant milestone in international cooperation for earth observation and meteorology. Its name combines “Megha” (Sanskrit for “cloud”) and “Tropiques” (French for “tropics”), aptly reflecting its scientific mission to investigate tropical weather phenomena.

Background and Objectives

The Megha-Tropiques mission was jointly developed by the Indian Space Research Organisation (ISRO) and the Centre National d’Études Spatiales (CNES), the French national space agency. The collaboration was initiated under a bilateral agreement signed in 2004, building upon the long-standing partnership between India and France in space research.
The tropics play a critical role in the global climate system, as they are the primary regions for evaporation, convection, and precipitation—processes that influence global circulation patterns. Prior to Megha-Tropiques, meteorological data on tropical weather systems were limited, especially concerning the diurnal cycle of rainfall and humidity.
The mission’s main objectives include:

• Understanding the hydrological cycle in the tropics, especially the relationship between humidity, radiation, and precipitation.
• Studying cloud formation and energy exchange between the ocean and atmosphere.
• Improving climate models by providing continuous and precise measurements of tropical weather systems.
• Contributing to global weather forecasting systems by offering near-real-time data on rainfall and energy fluxes.

Design and Technical Features

Megha-Tropiques was launched aboard PSLV-C18 from the Satish Dhawan Space Centre, Sriharikota, on 12 October 2011. The satellite was placed in a low Earth orbit of approximately 867 km altitude with an inclination of 20°, allowing it to make multiple passes over tropical regions each day.
Weighing about 1000 kilograms, the satellite was designed to operate for three years, though its mission extended well beyond its intended lifespan, continuing to provide valuable data for over a decade.
Key technical features included:

• Orbit Type: Near-equatorial orbit (low inclination), enabling frequent observation of tropical regions.
• Mission Duration: Initially 3 years, later extended multiple times due to excellent instrument performance.
• Data Downlink: Real-time transmission of data to ISRO and CNES ground stations for global dissemination.

Scientific Payloads

The Megha-Tropiques satellite carried four major scientific instruments, jointly developed by ISRO and CNES, to measure humidity, temperature, radiation, and rainfall:

1. MADRAS (Microwave Analysis and Detection of Rain and Atmospheric Structures):
   • A microwave imaging radiometer designed to measure rainfall intensity, cloud liquid water, and ice content.
   • It provided valuable data on convective systems and tropical cyclones.
   • Operated in multiple frequency bands (from 18 to 157 GHz).
2. SAPHIR (Sounder for Atmospheric Profiling of Humidity in the Intertropics by Radiometry):
   • A humidity sounder operating in the 183 GHz water vapour absorption band.
   • It measured humidity profiles at six different altitudes between the surface and the tropopause, improving understanding of moisture transport.
3. SCARAB (Scanner for Radiation Budget):
   • Measured the Earth’s radiation budget, including both shortwave solar radiation reflected by clouds and longwave infrared radiation emitted by the Earth.
   • Helped quantify the energy balance that drives tropical climate dynamics.
4. ROSA (Radio Occultation Sounder for the Atmosphere):
   • An Italian-built instrument used to study the temperature and pressure profiles of the atmosphere by analysing GPS signal refraction through atmospheric layers.

Together, these payloads enabled simultaneous observation of key meteorological parameters—humidity, rainfall, and radiation—providing a comprehensive picture of tropical weather behaviour.

Mission Achievements and Contributions

The Megha-Tropiques mission made several important contributions to meteorology, hydrology, and climate science:

• Enhanced Understanding of Monsoon Dynamics: Provided crucial data on the variability and spatial distribution of monsoon rainfall across the Indian Ocean and South Asian region.
• Study of Tropical Cyclones: Helped improve prediction models for cyclones by offering continuous observations of moisture and cloud formation.
• Global Climate Models: Contributed datasets for refining climate models used by international research institutions such as NASA, NOAA, and EUMETSAT.
• Collaboration with Global Weather Systems: Data from Megha-Tropiques was integrated into the Global Precipitation Measurement (GPM) programme, enhancing global precipitation monitoring.
• Radiation Budget Studies: Improved understanding of how tropical regions regulate global energy balance through the absorption and emission of radiation.

The satellite’s unique near-equatorial orbit allowed repeated coverage of the same region up to six times a day, far surpassing the temporal resolution of other polar-orbiting meteorological satellites. This feature was particularly valuable for studying the diurnal variation of tropical convection and rainfall, which changes rapidly within a 24-hour period.

Operational History and Data Sharing

After its launch, Megha-Tropiques was operated jointly by ISRO’s Satellite Centre (now URSC) and CNES’s Centre Spatial de Toulouse. The mission was part of the Global Earth Observation System of Systems (GEOSS) and contributed freely to the World Meteorological Organisation (WMO) network.
Its data were made available through the Meteorological and Oceanographic Satellite Data Archival Centre (MOSDAC) and used widely by researchers and forecasters worldwide. Despite the failure of the MADRAS instrument in 2013 due to technical issues, the other sensors—especially SAPHIR and SCARAB—continued to perform effectively for several years thereafter.

Decommissioning and Controlled Re-entry

After serving more than 11 years in orbit, far exceeding its design life, Megha-Tropiques was decommissioned in March 2023. In a landmark operation, ISRO conducted a controlled re-entry of the satellite to ensure it burned up safely upon re-entry into Earth’s atmosphere, minimising the risk of space debris.
This re-entry operation showcased India’s growing commitment to space sustainability and debris mitigation, marking one of ISRO’s first planned re-entries of a large satellite.

Significance and Legacy

The Megha-Tropiques mission holds enduring significance in the fields of atmospheric science, Earth observation, and international cooperation:

• Scientific Legacy: It provided one of the most detailed datasets on tropical humidity, rainfall, and radiation, aiding research on monsoon prediction, cyclone dynamics, and global energy balance.
• Technological Milestone: Demonstrated India’s capability in designing advanced meteorological satellites and precision orbit management.
• International Cooperation: Strengthened Indo-French collaboration in space research, setting a precedent for future joint missions like SARAL-AltiKa and TRISHNA.
• Environmental Responsibility: Its controlled re-entry established a model for sustainable space operations.