Rain Radar for Monsoon Precipitation Mission
- Paper number
IAC-07-B1.3.04
- Author
Mr. Eric Caubet, Thales Alenia Space, France
- Year
2007
- Abstract
Precipitation measurement and monitoring from space is crucial for many applications, specially in the context of climate change. The evolution of the monsoons is not predictable from the present models. Two conditions are required for precipitation measurement from satellites : a high time sampling rate, and accurate reference instruments allowing to calibrate the high rate observation systems. The TRMM radar is such a reference instrument, used to train the TRMM passive microwave instrument (TMI). One aim of Megha Tropiques is to increase the sampling capability of the passive microwave instrument (MADRAS). Simulations show that it will still be necessary to use Geostationary IR data, which reach a 15 minutes repetition time, as “interpolators”. Recently, rainfall algorithms were tested in the frame of the African monsoon experiment AMMA. The use of TRMM radar to train MSG precipitation detection led to an improvement of the rainfall accumulation estimations, but also allowed to derive a “precipitation efficiency” of different cloud systems. This comes in addition to the capacity of radars to derive the vertical profile of rainfall (which should be different over African squall lines and Indian monsoon systems). As TRMM will not last indefinitely, and GPM is not dedicated to the tropical areas, these considerations motivate the proposal of a new mission carrying a rain radar and a passive microwave imager for studying rainfall, specifically in Monsoon systems. The orbital inclination should be about 25° and the altitude 400 km to optimize rain radar performances. Studies using previous experience on different projects of satellite rain radars have been carried out and lead to a preliminary choice of solutions. The payload definition of what could be the Monsoon Precipitation Mission (MPM) following Megha Tropiques mission consists in associating a Ku-band rain radar scanning cross-track and a conventional conical scan microwave radiometer. Payload instruments should re-use as much as possible existing hardware and demonstrated techniques. The rain radar central electronics could be based on Alcatel Alenia Space altimeter product line and experience in pulse compression technique for meteorological radar acquired in previous ESA/CNES studies and breadboard. The high power amplification should re-use existing 140 W pulsed Ku-band Travelling Wave Tubes (TWTs). The rain radar antenna should preferably be of reflector type (short development plan) fed by a linear feed array to scan across-track. The radiometer could be based on Megha Tropiques radiometer. The swath of the radar would be 250 km and its horizontal resolution better than 5 km. Thanks to the on-board real time pulse compression, a vertical resolution of 60 m could be reached with on-board possibility of averaging to obtain 250 m resolution, and a rain rate greater than 60 mm/hr could be measured. The swath of the radiometer would be around 1000 km with a scan angle of 52.8°, and its resolution, depending on the channel, compatible with the radar footprint size. This paper explains the need of a rain radar satellite in a tropical orbit following TRMM and Megha-Tropiques missions and presents the preliminary payload definition with emphasis on the rain radar architecture, performances and existing/heritage space hardware.
- Abstract document
- Manuscript document
IAC-07-B1.3.04.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.