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| Titel |
Joint statistical correction of clutters, spokes and beam height for a radar derived precipitation climatology in southern Germany |
| VerfasserIn |
A. Wagner, J. Seltmann, H. Kunstmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 16, no. 11 ; Nr. 16, no. 11 (2012-11-07), S.4101-4117 |
| Datensatznummer |
250013561
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| Publikation (Nr.) |
 copernicus.org/hess-16-4101-2012.pdf |
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| Zusammenfassung |
First results of radar derived climatology have emerged over the last years,
as datasets of appropriate extent are becoming available. Usually, these
statistics are based on time series lasting up to ten years as continuous
storage of radar data was often not achieved before. This kind of
climatology demands a high level of data quality. Small deviations or minor
systematic under- or overestimations in single radar images become a major
cause of error in statistical analysis. Extensive corrections of radar data
are a crucial prerequisite for radar derived climatology.
We present a new statistical post-correction scheme based on a
climatological analysis of seven years of radar data of the Munich weather
radar (2000–2006) operated by DWD (German Weather Service). Original radar
products are used subject only to corrections within the signal processor
without any further corrections on single radar images. The aim of this
statistical correction is to make up for the average systematic errors
caused by clutter, propagation, or measuring effects but to conserve
small-scale natural variations in space.
The statistical correction is based on a thorough analysis of the different
causes of possible errors for the Munich weather radar. This analysis
revealed the following basic effects: the decrease of rain amount as a
function of height and distance from the radar, clutter effects such as
clutter remnants after filtering, holes by eliminated clutter or shading
effects from obstacles near the radar, visible as spokes, as well as the
influence of the bright band. The correction algorithm is correspondingly
based on these results. It consists of three modules. The first one is an
altitude correction which minimises measuring effects. The second module
corrects clutter effects and disturbances and the third one realises a mean
adjustment to selected rain gauges. Two different sets of radar products are
used. The statistical analysis as well as module 1 and module 2 of the
correction algorithm are based on frequencies of the six reflectivity levels
within the so-called PX product. For correction module 3 and for the validation of the
correction algorithm, rain amounts are calculated from the 8-bit so-called
DX product. The correction algorithm is created to post-correct climatological or
statistical analysis of radar data with a temporal resolution larger than
one year. The correction algorithm is used for frequencies of occurrence of
radar reflectivities which enables its application even for radar products
such as DWD's cell-tracking-product CONRAD.
Application (2004–2006) and validation (2007–2009) periods of this
correction algorithm with rain gauges show an increased conformity for radar
climatology after the statistical correction. In the years 2004 to 2006 the
Root-Mean-Square-Error (RMSE) between mean annual rain amounts of rain
gauges and corresponding radar pixels decreases from 262 mm to 118 mm
excluding those pairs of values where the rain gauges are situated in areas
of obviously corrupted radar data. The results for the validation period
2007 to 2009 are based on all pairs of values and show a decline of the RMSE
from 322 mm to 174 mm. |
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