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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 2 | Copyright

Special issue: Observing Atmosphere and Climate with Occultation Techniques...

Atmos. Meas. Tech., 11, 1181-1191, 2018
https://doi.org/10.5194/amt-11-1181-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Mar 2018

Research article | 01 Mar 2018

Reflected ray retrieval from radio occultation data using radio holographic filtering of wave fields in ray space

Michael E. Gorbunov1,2, Estel Cardellach3,4, and Kent B. Lauritsen5 Michael E. Gorbunov et al.
  • 1A. M. Obukhov Institute of Atmospheric Physics RAS, Moscow, Russia
  • 2Hydrometeorological Research Centre of Russian Federation, Moscow, Russia
  • 3Institut d'Estudis Espacials de Catalunya, Barcelona, Spain
  • 4Instituto de Ciencias del Espacio (ICE, CSIC), Barcelona, Spain
  • 5Danish Meteorological Institute, Copenhagen, Denmark

Abstract. Linear and non-linear representations of wave fields constitute the basis of modern algorithms for analysis of radio occultation (RO) data. Linear representations are implemented by Fourier Integral Operators, which allow for high-resolution retrieval of bending angles. Non-linear representations include Wigner Distribution Function (WDF), which equals the pseudo-density of energy in the ray space. Representations allow for filtering wave fields by suppressing some areas of the ray space and mapping the field back from the transformed space to the initial one. We apply this technique to the retrieval of reflected rays from RO observations. The use of reflected rays may increase the accuracy of the retrieval of the atmospheric refractivity. Reflected rays can be identified by the visual inspection of WDF or spectrogram plots. Numerous examples from COSMIC data indicate that reflections are mostly observed over oceans or snow, in particular over Antarctica. We introduce the reflection index that characterizes the relative intensity of the reflected ray with respect to the direct ray. The index allows for the automatic identification of events with reflections. We use the radio holographic estimate of the errors of the retrieved bending angle profiles of reflected rays. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.

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We apply linear and non-linear representations of wave fields, based on Fourier integral operators and Wigner distribution function, to the retrieval of reflected rays from radio occultation observations. We introduce a reflection index that characterizes the relative intensity of the reflected ray. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.
We apply linear and non-linear representations of wave fields, based on Fourier integral...
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