NWC REU 2010
May 25 - July 30



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Radar-Disdrometer Comparison to Reveal Attenuation Effects on CASA Radar Data

Christopher Kerr and Guifu Zhang


What is already known:

  • Dual-polarization X-Band radar allows the study of precipitation microphysics while producing high-resolution images.
  • This high resolution comes at the cost of severe attenuation.
  • Areas lacking multiple radar coverage are at a disadvantage since these radars may inaccurately estimate rainfall rates.

What this study adds:

  • This study compares radar and two-dimensional video disdrometer data to reveal attenuation effects on radar measurements.
  • The causes for large discrepancies between these measurements are investigated.


X-band radar provides a high resolution image at the cost of significant attenuation. This is due to the X-band's short wavelength. In this study, a two dimensional video disdrometer (2DVD) was deployed to the center of a triangle formed by three CASA dual-polarization X-band radars. The CASA radars provide measurements of reflectivity, differential reflectivity, specific differential phase, and copolar cross-correlation coefficient of precipitation. Using drop size distributions obtained from the 2DVD, the radar variables are calculated and treated as the ground truth. The radar and disdrometer measurements are compared to reveal discrepancies. Biases and errors are calculated, and possible causes are investigated. These results can be used to further minimize the attenuation obstacle in X-band radar.

Full Paper [PDF]