Definition and impact of a quality index for radar-based reference measurements in the H-SAF precipitation product validationNatural Hazards and Earth System Science, 13, 2695-2705, 2013Author(s): A. Rinollo, G. Vulpiani, S. Puca, P. Pagliara, J. Kaňák, E. Lábó, L'. Okon, E. Roulin, P. Baguis, E. Cattani, S. Laviola, and V. LevizzaniThe EUMETSAT Satellite Application Facility on Support to Operational
Hydrology and Water Management (H-SAF) provides rainfall estimations based
on infrared and microwave satellite sensors on board polar and geostationary
satellites. The validation of these satellite estimations is performed
by the H-SAF Precipitation Product Validation Group (PPVG). A common validation
methodology has been defined inside the PPVG in order to make validation
results from several institutes comparable and understandable.
The validation of the PR-OBS-3 (blended infrared–microwave (IR–MW) instantaneous rainfall
estimation) product using radar-based rainfall estimations as ground
reference is described herein. A network of C-band and Ka-band radars
throughout Europe ensures a wide area coverage with different orographic
configurations and climatological regimes, but the definition of a quality
control protocol for obtaining consistent ground precipitation fields across
several countries is required.
Among the hydro-meteorological community, the evaluation of the data quality
is a quite consolidated practice, even though a unique definition of a
common evaluation methodology between different countries and institutions
has not been set up yet.
Inside H-SAF, the first definition of the quality index of the radar
rainfall observations has been introduced at the Italian Civil Protection Department (DPC). In the evaluation of the DPC quality index, several
parameters are considered, some measured by the radar itself (static clutter
map, range distance, radial velocity, texture of differential reflectivity,
texture of co-polar correlation coefficient and texture of differential
phase shift) and some obtained by external sources (digital elevation model,
freezing layer height). In some cases, corrections were applied for clutter
and beam blocking.
The DPC quality index was calculated and applied to some relevant
meteorological events reported by a radar test site in Italy. The
precipitation field derived by radar data was compared with the PR-OBS-3
precipitation product, with varying thresholds of quality index: the impact
of the introduction of the quality index defined on the statistical results
of the satellite product validation as well as their sensitivity to the threshold
choice were thus evaluated. Results show that PR-RMSE (a relative RMSE here
introduced) is reduced from values between 2.5 and 3 to values around 1 when
the quality threshold is increased from 0 (no threshold) to 0.8. Fractional
standard error also decreases, from values around 2 to values around 1.5 in
the same span of the quality threshold.