Dual-Pol Radar 

 



The WSR-88D Doppler Radar in San Angelo (KSJT) is getting a facelift.  The current radar was installed in the mid 90s and has undergone several hardware upgrades and numerous software builds throughout the last 15 years but big changes are on the way.  In early April, the KSJT radar will be upgraded with dual-polarimetric, or dual-pol, technology.  This is an significant and exciting upgrade that will enhance the ability of the National Weather Service meteorologists to make warning decisions.  This technology will create 14 new products in addition to the dozens already available to NWS meteorologists. Technicians will take down the radar on April 4th, and the installation will take 2 weeks to complete.

So what is dual-pol radar and how does it differ from what we already have?  Some of this will be explained below.  Additional information can be found here.

KSJT WSR-88D
   KSJT WSR-88D near Mathis Field.



Traditional NWS Radar   Dual-Polarimetric Radar
WSR-88D   Dual Pol Radar
The current WSR-88D transmits radio waves oriented in a horizontal fashion.   The dual-pol radar will transmit radio waves oriented both horizonally and vertically.

 


 

So, now we know that dual-pol radars transmit both horizontally and vertically oriented radio waves.  How does this help?

Traditional NWS radars only transmit radio waves on the horizontal plane.  The returned energy generally provides a good indication of the intensity of the preciptation but does little to differentiate preciptation types or provide any information on the size or shape of the hydrometeors.  Dual-pol technology will help forecasters discriminate between heavy rain and hail or between rain and snow. 

The ability to discern the difference between rain and hail is a tremendous benefit when forecasting the onset of flash flooding.  Traditional radar rainfall estimates significantly over-estimate rainfall amounts when hail is present since water coated hail stones reflect a greater amount of radiation (hail contamination).  The dual-pol technology is able to remove the hail bias to provide much more accurate rainfall estimates, giving meteorologists near real-time access to this data.

 

Improvements we can expect with the dual-pol upgrade include:

Improved detection of rain, hail, snow and sleet
More accurate rainfall estimates
Detection of the melting layer
Identification of non-meteorological returns (birds, insects, chaff, debris, etc.)
Monitoring of aircraft icing conditions

 

While we will see improvements related to precipitation type discrimination and rainfall estimates, we do not anticipate an increase to tornado warning lead time.  The doppler technology will remain the same as with the traditional NWS radars.


 

Dual-Pol Products & Applications

The base radar products that have been available to users are base reflectivity, base velocity, and spectrum width.  Three new base products will be available after the dual-pol upgrade, including differential reflectivity (ZDR), correlation coefficient (CC), and specific differential phase (KDP).  In addition to these three new base products, there will be several dervied products.  These include a melting layer (ML) product, a hydrometeor classification algorithm (HCA) product, and eight new precipitation products.  Hover your mouse over the labels below to see examples of the three new dual-pol base products and a derived product called Hydrometeor Classification Algorithm (HCA).  Images courtesy of the Warning Decision Training Branch.

 

Differential Reflectivity

 

APPLICATIONS
Using differential reflectivity to identify a hail core
Using correlation coefficient to identify the melting layer and thunderstorm updrafts
Using specific differential phase to identify the melting layer and thunderstorm updrafts
Images courtesy of WDTB

 

The National Weather Service in San Angelo will make use of surrounding radars during the absence of the San Angelo WSR-88D.  These radars including Dyess AFB (KDYX), Midland (KMAF), Del Rio (KDFX) and Granger (KGRK).  These radars will sample the over the Concho Valley, Heartland and and Interstate 10 corridor at a greater altitude than the San Angelo radar, but we still get a good indication of the intensity and location of precipitation echoes.  Locations in the Big Country will see no temporary degredation in data since the Dyess WSR-88D is the radar of choice anyway! The only information that we will be missing is that closer to the ground so spotter reports will be important during this time.  Fell free to use the web storm report interface or give us a call at (325) 944-9445 if you have any information to share!  See the image for an idea of the locations of the surrounding radars (notice there is no data from KSJT in this image). 

 


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