 NEXRAD PMC approves polarimetric upgrade
to WSR-88D radar network
by Terry Schuur
For over 20 years, NSSL has been a leader
and major contributor to the scientific and engineering development
of polarimetric weather radar. This long history of accomplishment
was rewarded in the fall of 2003 when the NEXRAD Program Management
Committee (PMC) approved taking the first step towards upgrading the
operational WSR-88D network to include polarimetric capabilities. This
PMC decision, based on results from the year-long Joint Polarization
Experiment (JPOLE), represents a significant milestone in the continuing
evolution of the WSR-88D radar network.
JPOLE data collection and analysis
JPOLE, which was conducted from the Spring of 2002 through the Spring
of 2003, was designed to test the proof-of-concept polarimetric
KOUN WSR-88D radar engineering design, evaluate radar data quality,
demonstrate the utility and feasibility to operational users, and collect
data and information that could be used to perform a cost/ benefit
analysis.
The KOUN data archive from JPOLE contains an unprecedented
collection of exceptional quality polarimetric measurements of 98
events contatining meteorological and non-meteorological data. Using
this data set, analyses were conducted to demonstrate KOUN's ability
to provide improved Quantitative Precipitation Estimates, discriminate
between hydrometeor types, and eliminate non-meteorological artifacts.
Rainfall estimation was found to be dramatically improved in terms
of both bias and RMS (root mean square) error while classification
algorithms demonstrated great skill at pinpointing the location of
hail within storms, discriminating between snow and rain, identifying
the location of strong tornadoes, and improving data quality.
Operational
evaluation
The utility of polarimetric data to
operational forecasters was also examined
during JPOLE. A KOUN scanning
strategy was designed to emulate the
elevation angles, scanning rates, and
volume coverage times used by standard
WSR-88D radars. Real-time polarimetric
data and products were then supplied to
forecasters at the Norman, OK National
Weather Service (NWS) office. NSSL
observers assisted the forecasters in the
analysis and interpretation of the polarimetric
radar data and products during the
intense 3-month data collection period in
the Spring of 2003. In several instances,
KOUN data and products provided valueadded
information to the warning decision
process. For example, results of the
polarimetric rainfall accumulation
algorithm provided flash flood warning
guidance during several heavy rain events.
Hydrometeor classification algorithm
output were used to discriminate precipitation
types in winter storms and identify the
location of hail in severe convective
storms.
Network upgrade
Several NSSL reports documenting
JPOLE data collection and operations,
improvements in data quality, hydrometeor
discrimination, rainfall estimation,
and evaluation of the engineering design
are available on the JPOLE web site at
http://cimms.ou.edu/~schuur/jpole.
The polarimetric upgrade of the WSR-
88D network, supported by the NWS, the
Federal Aviation Administration, and the
Air Force Weather Agency through the
NEXRAD Product Improvement Program,
may ultimately prove as significant as the
nationwide upgrade to Doppler radar in
the 1980's. The first phase of the deployment
will utilize results obtained from
JPOLE to prepare system specifications
and identify procurement procedures
needed to move towards the pre-production
stage of the polarimetric upgrade,
eventually leading to full production. |
