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

Products Validation Report, 30 May 2010 - PVR-03 (Product PR-OBS-3) Page 26
meteorological environment, the Cloud Type product is the most useful as it distinguishes high-level
and optically thick clouds from medium- and low-level clouds; and optically thin clouds. It is also
useful for analyzing the cloud systems that have occurred at the time of satellite measurements.
SAFIR lightning system works operationally at Hungarian Meteorological Service. We have five
stations. The accuracy of the lightning network has been significantly increased the last two due to
the large amount of case studies investigated during summer periods. Therefore we intend to use the
lightning data, first of all in visual comparison as descriptor of the synoptic situation.
The main steps of the precipitation products validation procedure are:
Time and space alignment of the data from different sources, represented on different scales – pixel
size of radar and satellite data is not the same. Especially in the case of microwave measurements,
we have large footprints that need to be treated carefully. The time alignment can be solved by
simply matching the closest data available in time to the H-SAF products. There are advanced
methods to solve the up-scaling of ground and/or the down-scaling of satellite precipitation data.
The OMSZ-Hungarian Meteorological Service uses the techniques discussed and proposed by the
members of the validation group. We will contribute to the selection of the appropriate method and
to the investigation of the accuracy of the matching method.
The common task of the Precipitation Validation Group is the statistical validation. The up-scaling
method has a key role in this process. We can only compare the radar, satellite, raingauge, and
lightning if we have previously determined the coherent values from different sources. The data will
be collected into one file containing the following information to calculate statistic values either for
15 minutes samples, and for accumulated total precipitation information (over 3, 6, 12, 24 hours):
- radar-derived precipitation intensity,
- the satellite product values derived by H-SAF.
Statistical characteristics (RMS, BIAS, etc) will be then calculated between the satellite-based
precipitation and radar data for the different cases. These statistics will be performed for different
periods (months, summer-winter, day-night) as well as for some satellite pass in extreme cases .
We will also calculate multi-categorical statistics according to the classes determined by common
agreement by the validation group and the hydrologists. We will prepare contingency tables, scatter
plots and bias distribution functions to illustrate the performance of the precipitation products. These
statistics will be performed for different periods (months, summer-winter, day-night) and maybe for
some specific satellite passes. H-SAF data is going to be verified against radar data which preferably
will be adjusted to rain gauge data. Our radar data is already gauge-adjusted in the case of 12, and 24h
total precipitation.
The first task to the preparation of case studies is the selection of the periods with significant rain
amounts. This is done by the plotting of the radar and satellite rainfall estimate sums on a daily basis
of each month.
The second task to the preparation of case studies is the collection of all relevant data to the period
in question. This means the collect of radar, lightning data, and of MSG images and SAFNWC
products which correspond to the time period investigated.
The visual comparison including both rain gauge and radar data is an inevitable tool for the
understanding of the validation results of H-SAF products, because it:
- provides an overall picture of the H-SAF database (resolution, territories seen, general values)
- highlights similarities and differences in the structures and in the values
- helps to monitor the meteorological situation as well
To visualize the different products and to make subjective comparison we use the Hungarian Advanced
Weather Workstation (HAWK) developed by OMSZ-Hungarian Meteorological Service which can
interpret all kind of meteorological products together.