A key component of the Megha-Tropiques project is the Validation of the products and algorithms to ensure the highest quality. The validation plan has been designed in close link with the product developers in order to account for their specific need. The feedback loop from validation results to developers will be maintained throughout MT validation phase. The basis of validation is to compare MT measurements with reference data acquired through dedicated campaigns or from operational networks, round the tropics thanks to international collaborations.
MT Ground validation Super site and gages networks in West Africa
The French led effort for the Ground Validation of rainfall products and water vapor products is focused on West-Africa ; Africa is indeed the greatest continental surface in the Tropics. A super site is set up in Ouagadougou, with a polarimetric radar to acquire the high-resolution rainfields and vertical profiles that are needed to validate the Instant rainfall products, and intense radio-sounding campaigns for the validation of water vapor products. Several densified raingages network provide a high quality ground reference for the accumulated rainfall products. Operational weather services or regional organization provide larger scale data from gages network or radio-sounding. The data is quality-controlled, and then validation products (including the necessary error bars) are produced for comparison with MT satellite measurements.
MT Aircraft/radar based Microphysics Validation Campaigns
An important source of uncertainty in the rain retrieval from microwave radiometric measurements arises from a lack of information on the characteristics of the icy hydrometeors. Over land in particular, the radiometric signal sensed by MADRAS will come essentially from the ice phase (85GHz and 157GHz channels) and the rainfall profile below will be deduced from it. The radiometric signature of ice is related to both i) the density number of particles ii) the ice density of the particles. Both need to be well parameterized in the radiative transfer model included in the BRAIN retrieval scheme.
To address this important issue two specific campaigns combining aircraft based in situ information on the microphysics and radar observations have been organized. Both times the instrumented Falcone 20 from the French Airborne Environment Research Services (SAFIRE http://www.safire.fr/) was mobilized for 4 weeks, allowing more than 10 scientific flights. The campaigns combine i) direct but punctual information from dedicated aircraft sensors and ii) longer time series and extended 3D coverage provided by polarimetric radar retrieval to extend the statistics.
Other validation data sets and international collaborations
Important collaborative actions complement the French led MT GV dedicated sites and provide information from different eco-climatic zones. This is important to assess regional or rainfall regimes related bias in the products.
Collaborations are also being set up with several weather services and atmospheric research centers throughout the Tropical band ; this site will be updated when they will be formalized.
The Precipitation Measuring Missions Ground Validation meetings (PMM GV http://pmm.nasa.gov/science/ground-validation ) and validation activities in the framework of the International Precipitation Working Group IPWG (http://ipwg.isac.cnr.it/) offer great opportunities and resources for discussing validation issues, methodologies and to access reference data sets.
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