Chennai, Oct 10 (IANS): The countdown has begun for the launch Wednesday of an Indian weather satellite designed to help study climatic and atmospheric changes in the tropics.

"The countdown started at 9 a.m. and is proceeding smoothly. The filling of propellant in the fourth stage is on," an official of the Indian Space Research Organisation (ISRO) told IANS, speaking on condition of anonymity.

"All sub-systems will be checked during the countdown," the official added.

A Polar Satellite Launch Vehicle (PSLV) will blast off from Sriharikota, 80 km from here, at 11 a.m. on Wednesday to ferry the 1,000-kg Megha Tropique and three smaller satellites together weighing 45 kg.

Megha Tropiques is an Indo-French collaboration to study climatic and atmospheric changes in tropical regions and will make India the second nation in the world to launch such a space mission.

The Tropical Rainfall Measuring Mission (TRMM) -- a joint mission of NASA and the Japan Aerospace Exploration Agency (JAXA) designed to monitor and study tropical rainfall -- was launched Nov 27, 1997.

According to Indian space officials, ISRO will bear the launch cost of around Rs.90 crore while French space agency Centre National d'Études Spatiales (CNES) has spent around Rs.300 crore.

The CNES has built three instruments of Megha Tropiques: SAPHIR, SCARAB & GPS-ROS. The fourth, MADRAS, is a joint effort of ISRO and CNES.

The three nano satellites that will be ferried by the PSLV are the 10-kg SRMSAT built by students of SRM University near Chennai; the 3-kg remote sensing satellite Jugnu from the Indian Institute of Technology-Kanpur; and the 30-kg VesselSat from Luxumbourg to locate ships on high seas.

For ISRO, this will be the third rocket launch this year from India. In April, the agency successfully launched remote sensing satellite Resourcesat-2 and two others. In July, communication satellite GSAT-12 was put in orbit.