Graduate Exam Abstract
October 5, 2015, 2:00 pm - 4:00 pm
Morgan Library Rm 172
Attenuation Correction of X-band Polarimetric Doppler Weather Radar Signals: Application to Systems with High Spatio-Temporal Resolution
Abstract: In the last decade the atmospheric science community has seen widespread and successful
application of X-band dual-polarization weather radars for measuring precipitation in the lowest 2 km
of the troposphere. These X-band radars have the advantage of a smaller footprint, lower cost, and
improved detection of hydrometeors due to increased range resolution. In recent years, the hydrology
community began incorporating these radars in novel applications to study the spatio-temporal
variability of rainfall from precipitation measurements near the ground, over watersheds of interest.
The University of Iowa mobile XPOL radar system is one of the first to be used as an X-band
polarimetric radar network dedicated to hydrology studies. During the spring of 2013, the Iowa XPOL
radars participated in NASA Global Precipitation Measurement’s (GPM) first field campaign focused
solely on hydrology studies, called the Iowa Flood Studies (IFloodS).
Weather radars operating in the 3.2 cm (X-band) regime can suffer from severe attenuation,
particularly in heavy convective storms. This has led to the development of sophisticated algorithms
for X-band radars to correct the meteorological observables for attenuation. This is especially
important for higher range resolution hydrology-specific X-band weather radars, where the attenuation
correction aspect remains relatively unexamined. This research studies the problem of correcting for
precipitation-induced attenuation in X-band polarimetric weather radars with high spatio-temporal
resolution for hydrological applications. We also examine the variability in scattering simulations
obtained from the drop spectra measured by two dimensional video disdrometers (2DVD) located in
different climatic and geographical locations. The 2DVD simulations provide a ground truth for
various relations (e.g., AH-KDP and AH-ADP) applied to our algorithms for estimating attenuation, and
ultimately correcting for it to provide improved rain rates and hydrometeor identification.
We developed a modified ZPHI attenuation correction algorithm, with a differential phase constraint,
and tuned it for the high resolution IFloodS data obtained by the Iowa XPOL radars. Although this
algorithm has good performance in pure rain events, it is difficult to fully correct for attenuation and
differential attenuation near the melting layer where a mixed phase of rain and melting snow or
graupel exists. To identify these regions, we propose an improved iterative FIR range filtering
technique, as first presented by Hubbert and Bringi (1995), to better estimate the differential
backscatter phase, δ, due to Mie scattering at X-band from mixed phase precipitation.
In addition, we investigate dual-wavelength algorithms to directly estimate the α and β coefficients, of
the AH=αKDP and ADP=βKDP relations, to obtain the path integrated attenuation due to rain and wet
ice or snow in the region near the melting layer. We use data from the dual-frequency, dual-
polarization CHILL S-/X-band Doppler weather radar for analyzing the coefficients and compare their
variability as a function of height, where the hydrometeors are expected to go through a microphysical
transformation as they fall, starting as snow or graupel/hail then melting into rain or a rain-hail mixture.
The S-band signal is un-attenuated and so forms a reference for estimating the X-band attenuation
and differential attenuation. We present the ranges of the α and β coefficients in these varying
precipitation regimes to help improve KDP-based attenuation correction algorithms at X-band as well
as rain rate algorithms based on the derived AH.
Adviser: V. N. Bringi
Co-Adviser: Jose G. Colom
Non-ECE Member: Paul W. Mielke
Member 3: Anura Jayasumana
Addional Members: Ali Pezeshki
Mishra, K. V., W. F. Krajewski, R. Goska, D. Ceynar, B. Seo, A. Kruger, J. Niemeier, M. B. Galvez, V. N. Bringi, L. Tolstoy, “Deployment and performance analyses of high-resolution Iowa XPOL radar system during NASA IFloodS campaign,” Journal of Hydrometeorology, 2015; e-View doi: http://dx.doi.org/10.1175/JHM-D-15-0029.1
Thurai, M., V. N. Bringi, M. B. Galvez, K. V. Mishra, W. F. Krajewski, R. Goska, and W. A. Petersen, "Rainrate Algorithms using IFloodS campaign observations of S-band NPOL and Iowa XPOL Radars over a Network of 2DVideo Disdrometers," International Radar Conference on Weather Forecast and Hydrometeorological Applications, Nov. 2015, Jeju Island, South Korea (Accepted).
Thurai, M., V N Bringi, M. Galvez, K. V. Mishra, W. Krajewski, R. Goska, and W. Petersen, "S-band NPOL and Iowa XPOL radar observations over rain gauge and 2D video disdrometer networks during the IFloodS campaign," European Geosciences Union (EGU) General Assembly, April 12-17, 2015, Vienna, Austria.
Krajewski, W. F., K. V. Mishra, M. B. Galvez, R. Goska, M. Thurai, V. N. Bringi, L. Tolstoy, A. Kruger, and W. A. Petersen, "Salient observations and performance evaluation of Iowa XPOL radars during the NASA GPM IFloodS campaign," American Geophysical Union (AGU) Fall Meeting, Dec 15-19 2014, San Francisco, California.
Mishra, K. V., W. F. Krajewski, R. Goska., D. Ceynar, A. Kruger, M. B. Galvez, and V. N. Bringi, "Iowa X-band polarimetric radar data analyses: A selection of cases from IFloodS," Precipitation Measurement Missions (PMM) Science Team Meeting, Aug 4-8 2014, Baltimore, Maryland.
Galvez, M. B., J. G. Colom, V. Chandrasekar, F. Junyent, S. Cruz-Pol, R. A. Rodriguez Solis, L. Leon, J. J. Rosario-Colon, B. De Jesus, J. A. Ortiz, K. M. Mora Navarro, “First observations of the initial radar node in the Puerto Rico TropiNet X-band polarimetric Doppler weather testbed,” IGARSS, 2013.
Galvez, M. B., "The development and validation of an X-band dual polarization Doppler weather radar test node for a tropical network," Master of Science Thesis, Colorado State University Libraries, 2012.
Galvez, M. B., J. G. Colom, V. Chandrasekar, F. Junyent, S. Cruz-Pol, R. A. Rodriguez Solis, Ki-Ryong Kwon, “First Observations of an X-Band dual polarization Doppler weather radar on the western coast of Puerto Rico,” IGARSS, 2011.
Galvez, M. B., J. G. Colom, V. Chandrasekar, F. Junyent, S. Cruz-Pol, R. A. Rodriguez Solis, “Salient Features of the Radar Nodes in the Puerto Rico Tropical Weather Testbed,” IGARSS, 2009.
Program of Study: