Identifying insects, clouds, and precipitation using vertically pointing polarimetric radar Doppler velocity spectra
<p>This study presents a method to identify and distinguish insects, clouds, and precipitation in 35 GHz (Ka-band) vertically pointing polarimetric radar Doppler velocity power spectra and then produce masks indicating the occurrence of hydrometeors (i.e., clouds or precipitation) and insects...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2021-06-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | https://amt.copernicus.org/articles/14/4425/2021/amt-14-4425-2021.pdf |
Summary: | <p>This study presents a method to identify and distinguish
insects, clouds, and precipitation in 35 GHz (Ka-band) vertically pointing
polarimetric radar Doppler velocity power spectra and then produce masks
indicating the occurrence of hydrometeors (i.e., clouds or precipitation)
and insects at each range gate. The polarimetric radar used in this study
transmits a linear polarized wave and receives signals in collinear (CoPol)
and cross-linear (XPol) polarized channels. The measured CoPol and XPol
Doppler velocity spectra are used to calculate linear depolarization ratio
(LDR) spectra. The insect–hydrometeor discrimination method uses CoPol and
XPol spectral information in two separate algorithms with their spectral
results merged and then filtered into single value products at each range
gate. The first algorithm discriminates between insects and clouds in the
CoPol Doppler velocity power spectra based on the spectra texture, or
spectra roughness, which varies due to the scattering characteristics of
insects vs. cloud particles. The second algorithm distinguishes insects
from raindrops and ice particles by exploiting the larger Doppler velocity
spectra LDR produced by asymmetric insects. Since XPol power return is
always less than CoPol power return for the same target (i.e., insect or
hydrometeor), fewer insects and hydrometeors are detected in the LDR
algorithm than the CoPol algorithm, which drives the need for a CoPol based
algorithm. After performing both CoPol and LDR detection algorithms, regions
of insect and hydrometeor scattering from both algorithms are combined in
the Doppler velocity spectra domain and then filtered to produce a binary
hydrometeor mask indicating the occurrence of cloud, raindrops, or ice
particles at each range gate. Forty-seven summertime days were
processed with the insect–hydrometeor discrimination method using US
Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program
Ka-band zenith pointing radar observations in northern Oklahoma, USA. For
these 47 d, over 70 % of the hydrometeor mask column bottoms were
within <span class="inline-formula">±</span>100 m of simultaneous ceilometer cloud base heights. All
datasets and images are available to the public on the DOE ARM repository.</p> |
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ISSN: | 1867-1381 1867-8548 |