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| Titel |
Improved rainfall estimates in convective storms using polarisation diversity radar |
| VerfasserIn |
A. J. Illingworth, T. M. Blackman, J. W. F. Goddard |
| 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 ; 4, no. 4 ; Nr. 4, no. 4, S.555-563 |
| Datensatznummer |
250001879
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| Publikation (Nr.) |
 copernicus.org/hess-4-555-2000.pdf |
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| Zusammenfassung |
| Errors arise when using conventional radar
reflectivity, Z, to estimate rainfall rate, R, and these can be particularly
severe during severe convective storms; the very events when accurate estimates
are needed so that action can be taken to mitigate the effects of flooding.
Concentration is on three problems associated with heavy rainfall: hail,
attenuation and absolute calibration of the radar, and consider how polarisation
radar parameters, differential reflectivity, ZDR, and specific
differential phase shift KDP, might lead to their alleviation. It is
essential to consider the fundamental limits to the accuracy with which these
parameters can be estimated. If ZDR
can be measured to an accuracy of 0.2 dB, then it provides a measure of mean
raindrop shape which is sufficiently precise to improve rainrate estimates. This
can be achieved at S-band (10 cm), but seems very difficult for operational
C-band (5 cm) radars; differential attenuation by the heavy rain introduces a
negative bias into ZDR
which increases with range. However, the magnitude of this bias at C-band can
then be used to correct for the total attenuation of Z. Differential phase, KDP
has the advantage that it is a phase measurement and so is unaffected by
attenuation. It only responds to the rainfall and is unaffected by the hail, but
KDP is a noisy parameter and is only useful for heavy rainfall above
30 – 60 mm hr-1. Fortuitously, KDP and ZDR
are not independent and one use of KDP and ZDR
may well be to exploit this redundancy to identify rain areas as opposed to
hail, and in rainfall to use the redundancy to provide an automatic calibration
of the absolute reflectivity, Z, to 0.5 dB (12%). Finally, the noisy character
of both ZDR and KDP together
with the low level of the co-polar correlation coefficient provide the first
reliable means of detecting and removing anomalous propagation which is a major
operational problem for all weather radars.
Keywords: polarisation radar, rainfall calibration, attenuation, hail,
anomalous propagation |
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