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A first approach to unsupervised
Entropy-Alpha-classification of full-polarimetric
weather-radar data
Thomas Börner(1), Martin Hagen(2), David
Bebbington(3) Deutsches Zentrum für Luft- und
Raumfahrt e.V. (DLR) (1)Institut für
Hochfrequenztechnik und Radarsysteme, (2)Institut
für Physik der Atmosphäre P.O.-Box 1116, D-82230
Weßling, Germany, Phone/Fax [phone] /
-1449, Email Thomas.Boerner_at_dlr.de (3)University
of Essex, Electronic Systems Engineering
Department, UK

• Abstract In this contribution we will show a
  first approach of unsupervised classification of
  weather-radar data using the polarimetric
  Entropy-Alpha target decomposition (Cloude,
  Pottier, 1997). The classification algorithm
  consists of the following steps
• Prepare the polarimetric time series data (DLRs
  POLDIRAD) correct phase changes due to
  propagation and Doppler effects on a pulse to
  pulse basis.
• Calculate the Covariance (or Coherence) matrix
  from the S matrix. Ensemble averaging preserves
  statistical fluctuations of targets over time.
• Diagonalisation of the hermitian Covariance
  matrix yields dominant physical scattering
  mechanisms, represented and interpreted by
  Entropy H and Alpha-angle a.
• Choose areas in the H-a plane for classification.
  Refinement is done by adding copolar reflectivity
  Z to the classification scheme.

Entropy Alpha Target Decomposition
Simplified interpretation of a ellipticity of
scattering objects.
Physical scattering mechanisms
Degree of disorder in the scattering process.
Contribution of each scattering mechanism
RHI classification result
PPI classification result
Classification Scheme c1 0 ? H ? 0.4 0 ?
a ? 20 10 dbZ ? Zyy ? 22 dbZ c2 0 ? H ?
0.4 20 ? a ? 50 10 dbZ ? Zyy ? 22 dbZ c3 0.4
? H ? 1 10 ? a ? 20 10 dbZ ? Zyy ? 22 dbZ c4
0 ? H ? 0.45 0 ? a ? 20 22 dbZ ? Zyy ?
35 dbZ c5 0 ? H ? 0.45 20 ? a ? 50 22 dbZ
? Zyy ? 35 dbZ c6 0.45 ? H ? 1 0 ? a ?
20 22 dbZ ? Zyy ? 35 dbZ c7 0.45 ? H ? 1 20 ?
a ? 50 22 dbZ ? Zyy ? 35 dbZ c8 0.6 ? H ?
1 15 ? a ? 50 35 dbZ ? Zyy ? 64 dbZ c9 0
? H ? 1 0 ? a ? 50 0 dbZ ? Zyy lt 10 dbZ
H-a plane
H-a plane
Z-H plane
Z-H plane
Z-a plane
Z-a plane