Megha-Tropiques

Megha-Tropiques is a space mission jointly managed by the space agencies CNES and ISRO. This mission is designed to study the convective systems of the atmosphere and more particularly the analysis of the water cycle through the transport and distribution of water vapor, the life cycle of convective systems and energy exchanges in the equatorial belt. The tropical zones are those where the most important energy exchanges occur: radiative exchanges, latent heat exchanges, transport of constituents and energy through dynamic processes. The challenge is therefore to increase knowledge of hydrological and energy processes in the tropics and their influence on the global circulation of the atmosphere, that the oceans, and climatic variations.

Note: Megha means “cloud” in Sanskrit; Tropiques is the French word for “tropics”.

Thanks to its circular orbit inclined 20° to the equator, which provides frequent sampling of the tropical regions, Megha-Tropiques is a unique satellite for climate research that also aids scientists seeking to refine prediction models.

Main Megha-Tropiques orbit parameters:

• Circular orbite
• Orbital period: 102 min. (~14 rev./day)
• Altitude: 867 km
• Inclination: 20°
• Cycle : 7 days

The equatorial region up to about ±23º can be visited at least three times daily (important to follow the life cycle of the mesoscale convective systems). Even more, repeated observations 6 times a day over the 10º–20º latitude band are accessible.

Observations can be divided into three categories:

• Collection of long-term measurements with good temporal distribution and a good coverage of tropical latitudes to better understand the processes related to large tropical convective systems and their life cycle.
• Improved determination of water masses and energy quantities at different spatial and temporal scales.
• Significant statistics on the conditions under which convective systems are formed and evolve, by analyzing their interaction with the atmospheric circulation, studying annual and seasonal variations and the diurnal cycle of these systems. This will allow the refinement of weather and climate models and the integration of convective data into weather forecasting models.

The ambition of the Megha-Tropiques mission is therefore to obtain significant advances in the understanding of the effects of these convective systems on the tropical climate and to increase the community’s capacity to predict them at different spatio-temporal scales.

Satellite

The spacecraft consists of two major modules: the platform, provided by ISRO and heritage of IRS satellite series, and the Payload Instrument Module (PIM) which support the four scientific instruments.

The main characteristics of the satellite are:

Lift-off mass: 997 kg – Power 1160 W – 3-axis stabilised with 4 reaction wheels, gyros and star sensors.

It was launched on October 12, 2011 on indian PSLV launch vehicle.

Since 2018, the mission has been impacted by a problem affecting the data recording in the mass memory (BDH). In order to avoid corrupted data, the BDH equipment must be regularly turned off and operates on a 90min. ON/300min. OFF cycle. The consequence is a duty cycle of scientific data lower than 25%, and which, combined with other unavailability items, actually oscillates between 10 and 25% depending on the period.

Playload

A dedicated carbon fiber module, the PIM, facilitates the integration of the instruments onto the main platform. It also ensures thermal decoupling and the electrical and mechanical interface between the payload and the platform.

Megha-Tropiques carries the following four instruments:

• MADRAS (Microwave Analysis and Detection of Rain and Atmospheric Structures), a microwave imager aimed mainly at studying precipitation and clouds properties – developed jointly by CNES and ISRO
• SAPHIR (Sounder for Probing Vertical Profiles of Humidity), a 6 channels microwave radiometer for the retrieval of water vapour vertical profiles and horizontal distribution – CNES instrument
• SCARAB (Scanner for Radiation Budget), a radiometer devoted to the measurement of the radiative budget at the top of the atmosphere – CNES instrument
• ROSA (Radio Occultation Sensor for Atmosphere), a GPS radio-occultation receptor for vertical profiling of temperature and humidity of the atmosphere – ISRO instrument

Only MADRAS, SAPHIR et SCARAB data are managed by AERIS

Products

The AERIS ICARE Data and Service Center archives and distributes Megha-Tropiques Level 1 and Level 2 products.

Level 1 processing is performed by ISRO and the data are transmitted to ICARE via a dedicated line. They are available by acquisition segment or by complete orbit and in scan mode (sensor geometry) or resampled in a common grid for all instruments.

The scientific processing of Level 2 products is performed by ICARE. The products are archived and distributed by ICARE.

In addition, ICARE produces the TAPEER (Tropical Amount of Rainfall with Estimation of ERors) product which is a level 4 product combining SAPHIR data with those of other microwave instruments of the GPM constellation and with data from the corona of meteorological geostationary satellites.

See also the SAPHIR, MADRAS, SCARAB products.

Data access

Http download links:

http://www.icare.univ-lille1.fr/mt/access

Information links

http://www.icare.univ-lille1.fr/mthttp://meghatropiques.ipsl.polytechnique.fr/

Contacts

Point of contact

Rémy Roca (Laboratoire d’Etudes en Géophysique et Océanographie Spatiales)

remy.roca@legos.obs-mip.fr Scientific coordinator

Michel Dejus (CNES project manager)

michel.dejus@cnes.fr