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

Products Validation Report, 30 May 2010 - PVR-03 (Product PR-OBS-3) Page 28
be calculated to quantify the similarity of two images. In case of two classes of precipitation the
suggested parameters are: FAR, POD, BIAS, ETS and HSS. In case of more than two classes the
useful parameters are: HSS and correlation coefficient.
For a reliable validation plan an ensemble of cases (each of them consisting in estimated and “truth‟
maps) have to be considered. The larger the ensemble is the more reliable the validation is. The visual
comparison for several pairs of images become not easy and therefore only the 2 and 3 procedures are
suggested. However it does worth to mention that there are two ways to carry out those procedures: a)
all the pixels from the ensemble of cases are considered together. We obtain an ensemble of pixels of
satellite precipitation estimation and an ensemble of pixels of precipitation “truth”. The two ensemble
are compared by calculating the previously indicated parameters. b) for each case the comparison is
carried out by calculating the above statistics parameters. The average values of those statistics
parameters are calculated over the ensemble of cases.
It is also suggested to carry out the validation for two different areas: sea and land. This because the
precipitation “truth” over the land is mainly based on raingauges whereas for the sea only radar
estimation are available. A further distinction will be made considering orography, by using a digital
elevation model (e.g. GTOPO30 by the U.S. Geological Survey).
Validation: complete plan
The precipitation “truth” data set is built for a complete year at 15 minutes of time resolution.
Instantaneous rain validation (MW algorithm): all the polar satellite overpasses over Italy during the
considered year can be collected and used to generate the corresponding MW-based precipitation
estimation. All of them can be validated. MW+IR algorithm: for each time of the day and for each
day of the year it is possible to validate the MW+IR-based precipitation estimation. In this case the
variability of performance along the day and along the year can be assessed. Moreover the
degradation of MW+IR performance far from the MW overpass can be evaluated.
Cumulated rain validation (MW+IR algorithm): cumulated estimated rain at 3, 6, 12 and 24 hours
intervals can be validated by using the corresponding cumulated “truth” rain. The variability of
performance along the year can be assessed as well.
Validation: minimal plan
The precipitation “truth” data set is built for summer and winter at around 12 and 24 UTC.
Instantaneous rain validation (MW algorithm): all the polar satellite overpasses over Italy in that
period can be collected and used to generate the corresponding MW-based precipitation estimation.
All of them can be validated.
Instantaneous rain validation (MW+IR algorithm): for 12 and 24 UTC times and for each day of
summer and winter it is possible to validate the MW+IR-based precipitation estimation. In this case
it is expected to get information about the maximum variability of performance.
Cumulated rain validation (MW+IR algorithm): cumulated estimated rain at 3,6,12 and 24 hours
intervals for summer and winter can be validated by using the corresponding cumulated “truth” rain.
Validation: specific plan
The precipitation “truth” data set is built for particular region of Italy and/or for particular month and/or
particular time of the day.
Instantaneous rain validation (MW algorithm): all the polar satellite overpasses over that region and
in that period can be collected and used to generate the corresponding MW-based precipitation
estimation. All of them can be validated. MW+IR algorithm: for that region and that period it is
possible to validate the MW+IR-based precipitation estimation.
Cumulated rain validation (MW+IR algorithm): cumulated estimated rain at 3, 6, 12 and 24 hours
intervals for that region and that period can be validated by using the corresponding cumulated
“truth” rain.