MT validation | MT validation |
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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://www.isac.cnr.it/~ipwg/validation.html)
offer great opportunities and resources for
discussing validation issues,
methodologies and to access reference data sets.
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| Last Updated ( Monday, 25 June 2012 ) |
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