Evaluation of Germany's network radar composite rain producs with GPM
near surface precipitation estimations
Abstract
The Global Precipitation Measurement core satellite (GPM) has been
collecting high quality precipitation data since 2014 over the globe
with its Dual-frequency Precipitation Radar (DPR; Ku-band and Ka-band).
Specificly over Germany, GPM provides data with typically two daily
overpasses. Thus providing a unique opportunity to have a satellite
based standard for estimation of precipitation in order to compare and
evaluate ground-based radar network counterpart products. The German
national weather service (DWD, Deutscher Wetterdienst) provides
precipitation observations from its operational radar network RADOLAN as
a composite products derived from 17 dual-pol C-band radars. The RADOLAN
(RY) regular products are Germany-wide composites of precipitation
estimates based on a set of precipitation type dependent Z-R
relationships derived for liquid hydrometeors applied to radar
reflectivity after clutter- and beam blockage-corrections. In this
contribution we focus to compare three years of GPM DPR and RADOLAN
precipitation products. This allows us to evaluate at which extend these
two Near Surface products are consistent when observed from different
geometries and obtained by independent instruements and retrieval
methods. We quantify the uncertainties when directly comparing the DPR
near surface product with RY. It is shown that a direct comparisons
might not take into account a set of uncertainties originated from the
scans geometry from DPR and RADOLAN, precipitation types, and sampling
volumes. Therefore we suggest an adjusted DPR product, which is
extracted from the DPR vertical profiles and adapted to fit the specific
RY measurement configuration e.g. scans height and beam width. This
allows a much more detailed classification of the hydrometoer phases per
measuring volume, which we define as non-uniform phase beam filling
(NPBF). The NPBF gives information about the ratio of liquid, solid or
mixed hydrometeors in a given volume. Orographic, synoptic,
microphysical influences as well as NPBF effects are examined and their
uncertainties introduced on a direct comparison of satellite with
ground-based producs are put into consideration. The adaptation of the
DPR precipitation products to the specific scan geometry of the
individual ground radars improves the correlation and reduce the RMSE.