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| Titel |
A novel approach for absolute radar calibration: formulation and theoretical validation |
| VerfasserIn |
C. Merker, G. Peters, M. Clemens, K. Lengfeld, F. Ament |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 6 ; Nr. 8, no. 6 (2015-06-22), S.2521-2530 |
| Datensatznummer |
250116437
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| Publikation (Nr.) |
 copernicus.org/amt-8-2521-2015.pdf |
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| Zusammenfassung |
The theoretical framework of a novel approach for absolute radar calibration
is presented and its potential analysed by means of synthetic data to lay out
a solid basis for future practical application. The method presents the
advantage of an absolute calibration with respect to the directly measured
reflectivity, without needing a previously calibrated reference device. It
requires a setup comprising three radars: two devices oriented towards each
other, measuring reflectivity along the same horizontal beam and operating
within a strongly attenuated frequency range (e.g. K or X band), and one
vertical reflectivity and drop size distribution (DSD) profiler below this
connecting line, which is to be calibrated. The absolute determination of
the calibration factor is based on attenuation estimates.
Using synthetic, smooth and geometrically idealised data, calibration is found
to perform best using homogeneous precipitation events with rain rates high
enough to ensure a distinct attenuation signal
(reflectivity above ca. 30 dBZ). Furthermore, the choice of the interval width (in
measuring range gates) around the vertically pointing radar, needed for
attenuation estimation, is found to have an impact on the calibration results.
Further analysis is done by means of synthetic data with realistic,
inhomogeneous precipitation fields taken from
measurements. A calibration factor is calculated for each considered
case using the presented method. Based on the distribution of the
calculated calibration factors, the most probable value is
determined by estimating the mode of a fitted shifted logarithmic
normal distribution function. After filtering the data set with
respect to rain rate and inhomogeneity and choosing an appropriate
length of the considered attenuation path, the estimated uncertainty
of the calibration factor is of the order of 1 to 11 %,
depending on the chosen interval width. Considering stability and
accuracy of the method, an interval of eight range gates on both sides
of the vertically pointing radar is most appropriate for
calibration in the presented setup. |
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