H-SAF Product Validation Report (PVR) PR-OBS-3

Products Validation Report, 30 May 2010 - PVR-03 (Product PR-OBS-3) Page 32
Methods
Satellite data are usually the raster data with defined projection and pixel size/resolution. Radar data are
also raster data, but usually in a different projection and resolution from satellite data. Therefore the first
step is to transform both data to the common projection and pixel resolution map optimal for data
comparison. SHMÚ has good experiences how to perform necessary re-projections operationally.
Raingauge data are point data, which can be mapped by means of 2D or 3D interpolation which use the
method of regularised splain with tension. When 3D interpolation is used, orography is reflected in the
outputs. This method is generally called kriging. In this way, the original point data are transformed to
the raster file comparable with satellite and radar data (see Fig. 20).
Fig. 20 - Example of 5-days cumulative precipitation constructed from raingauge measurements by means of 3D
extrapolation method.
Radar data should be validated and adjusted before being used for the validation of other products.
SHMÚ has made calibration study on radar site Maly Javornik based on regression between set of
raingauges and radar 24-hour precipitation products in 150 km radar range few years ago. The
corrections on distance from radar and partial beam blockage by terrain were subject of this study. We
plan to make similar study for the whole territory of Slovakia. Output should be used for the operational
calibration and quality control of radar precipitation measurements. We are also planning to test method
for precipitation estimation based on polarisation techniques for new radar in eastern part of Slovakia.
Quality control of radar data will be based on NWC SAF products like cloud types classification and
products containing information about water content in vertical column.
SHMÚ is planning to use three methods to perform final validation of satellite precipitation products:
Direct comparison of satellite data with point raingauge measurements, calculation of standard
statistical parameters RMSE, ME and other.
Comparison of satellite raster data with precipitation raster based data (interpolated raingauges,
corrected radar precipitation fields,…) and with calculation of standard statistical parameters.