83rd Annual

Sunday, 9 February 2003
Megha-Tropiques for meteorological observations in the tropics
Bharat Khushalani, University of Southern California, Los Angeles, CA; and J. Srinivasan and G. Raju
Most of the satellites that have been launched to observe the variations in temperature, cloudiness, rainfall, water vapor and other parameters that influence our weather and climate are in geostationary or sun-synchronous polar orbits. The spatial resolution of geosync satellites cannot be as good as satellites at low altitudes. The signal-to-noise ratio of visible, infrared or microwave radiation is quite low in geosync satellites which precludes the use of microwave sensors.

Sun-sync polar orbit satellites, on the other hand, cannot observe a given region more than twice in 24 hours. Since tropical convective systems evolve very rapidly, it is important to observe these systems as frequently as possible. A microwave sensor is essential if parameters such as sea surface temperature must be observed during cloudy periods. The high temporal and spatial resolution that is neccessary to observe tropical convective system can be achieved if the satellite is launched in Low Inclination Low Earth Orbit (LILEO). A LILEO satellite cannot observe polar regions and hence is suitable for the study of tropical regions only.

In the last two decades there has been an increasing realization of the role played by tropical convective systems in modulating the weather and climate in tropics and extra-tropics. During this period, the impact of El-Nino all around the world was studied using satellite and in-situ observations as well as computer models. While Earth Radiation Budget Satellite (ERBS) was a high 57-degree inclination satellite, Tropical Rainfall Measuring Mission (TRMM) was launched in LILEO (35-degree inclination) to give higher temporal resolution in the tropics. Indian Space Research Organization (ISRO), in joint collaboration with French Space Agency, Center National d'Etudes Spatiales (CNES), will be launching a satellite specifically designed to obtain energy and moisture budget of tropical convective systems. This LILEO satellite, Megha-Tropiques, will have sensors to measure sea surface temperature, radiative fluxes, cloudiness, surface winds, water vapor and liquid water content. In this paper, we will examine the effect of orbital parameters of Megha-Tropiques on the temporal sampling rate.

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