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Degree of Polarization: Theory and Applications for weather radar at hybrid mode

Galletti, Michele and Bebbington, David and Chandra, Madhukar and Börner, Thomas (2008) Degree of Polarization: Theory and Applications for weather radar at hybrid mode. In: Proceedings of the European Conference on Radar in Meteorology and Hydrology (ERAD). Proceedings of the European Conference on Radar in Meteorology and Hydrology (ERAD), 2008-06-30 - 2008-07-04, Helsinki, Finland.

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Official URL: http://www.fmi.fi/weather/rain_13.html

Abstract

In this work, fully polarimetric data from POLDIRAD (DLR C-band research weather radar) are used to evaluate the degree of polarization of weather radar targets. The degree of polarization can be derived from Wolf’s coherency matrix and, for a given incoherent target, is dependent on the transmit polarization state. However, thanks to unitary transformations, fully polarimetric data allow the retrieval of the degree of polarization corresponding to any desired transmit state. The concept of depolarization response, indicated with p(χ , ψ), is introduced to illustrate this dependency, and computed depolarization response graphs are shown for canonical incoherent scatterers. Canonical incoherent scatterers are constructed as discrete sums of clouds of canonical (coherent) scatterers and are used to illustrate the behaviour of the degree of polarization at different transmit states for both anisotropic and isotropic weather targets. The degree of polarization is then compared with the copolar correlation coefficient, a variable already in use in radar meteorology, in order to assess whether it brings complementary information or not. When rain is illuminated, if the transmit state lies on the circular/slant circle of the Poincare sphere, (the great circle passing through the poles and +/- 45 linear polarization) we experimentally and theoretically show that the degree of polarization performance is very similar to the copolar correlation coefficient and, indeed, the capability of carrying complementary information to the set of variables normally available to dual-pol radars at hybrid is limited. However, exploration of fully polarimetric weather radar data reveal that these variables can differ. Experimental data are shown and possible physical mechanisms explaining these unexpected differences are discussed. Besides cloud microphysics research, the results might be relevant also for operational purposes because planned weather radars are supposed to operate at hybrid mode. Together with the copolar correlation coefficient, the degree of polarization at circular/slant send is naturally available to these radars and the use of the latter might bring additional information essentially at zero cost. For a sound evaluation of the utility of the degree of polarization at circular/slant send, it must not be forgotten that the copolar correlation coefficient measured by hybrid radars differs from the copolar correlation coefficient measured at alternate H/V mode. Since the copolar correlation coefficient used in the present work is collected at alternate H/V transmit mode, further research is needed for a more precise assessment of the potential to bring complementary information.

Document Type:Conference or Workshop Item (Speech)
Title:Degree of Polarization: Theory and Applications for weather radar at hybrid mode
Authors:
AuthorsInstitution or Email of Authors
Galletti, MicheleUNSPECIFIED
Bebbington, DavidUniversity of Essex, UK
Chandra, MadhukarTU-Chemnitz
Börner, ThomasUNSPECIFIED
Date:July 2008
Journal or Publication Title:Proceedings of the European Conference on Radar in Meteorology and Hydrology (ERAD)
Refereed publication:No
In ISI Web of Science:No
Status:Published
Keywords:depolarization response, degree of polarization, fully polarimetric weather radar
Event Title:Proceedings of the European Conference on Radar in Meteorology and Hydrology (ERAD)
Event Location:Helsinki, Finland
Event Type:international Conference
Event Dates:2008-06-30 - 2008-07-04
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben SAR-Expert-Support-Lab (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Microwaves and Radar Institute > Radar Concepts
Microwaves and Radar Institute
Deposited By: Michele Galletti
Deposited On:31 Jul 2008
Last Modified:12 Dec 2013 20:32

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