The dual-polarization radar upgrades to the Fort Polk (KPOE) and Lake Charles (KLCH) WSR-88D Doppler radars are getting ready to begin. The KPOE radar will be out of service for one to two weeks, returning to service as late as February 15th. KLCH will undergo its upgrade shortly after KPOE is returned to service. KLCH will likely return to service by February 28, 2013. Click here for access to radar data from nearby sites as well as other locations around the United States. During this time, radar data from the KPOE and KLCH radar will be unavailable and other surrounding radars will have to be used. This upgrade will incorporate a new technology called dual-polarization, or dual-pol, that is part of the NWS vision to build a weather-ready nation to better protect lives and livelihoods. The new technology will result in 14 new radar products that will enable us to continue providing our suite of high quality products and services to the citizens of Southwest Louisiana and Southeast Texas. This upgrade will help forecasters identify the type of precipitation that is falling as well as improve rainfall estimates.
We strongly encourage all users of these new products to complete a series of online training modules that were recorded by the Warning Decision Training Branch (WDTB). Modules are available for non-NWS meteorologists and non-meteorologists through this website.
What is Dual-Pol?
The current doppler radars transmit and receive pulses of radio waves in a horizontal orientation. As a result, the radar only measures the horizontal dimensions of targets (e.g. cloud and precipitation droplets). Dual-polarimetric radar transmits and receives pulses in both a horizontal and vertical orientation. Therefore, the radar measures both the horizontal and vertical dimensions of targets. Since the radar receives energy from horizontal and vertical pulses, we can obtain better estimates of the size, shape, and variety of targets. It is expected that this will result in significant improvements in the estimation of precipitation rates, the ability to discriminate between precipitation types (e.g. hail vs. rain), and the identification of non-meteorological returns.
Current NWS doppler radar
Dual Polarization Technology As Explained by "That Weather Show"
Benefits of Dual-Pol
Improved accuracy of precipitation estimates, leading to better flash flood detection
Ability to discern between heavy rain, hail, snow, and sleet
Improved detection of non-meteorological echoes (e.g. ground clutter, chaff, anomalous propagation, birds, and tornado debris)
Detection of aircraft icing conditions
Identification of the melting layer (e.g. bright band)
Dual-Pol will not improve tornado lead times or be able to provide exact precipitation type on the ground.
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.
Specific Differential Phase
Hydrometeor Classification Algorithm
Using correlation coefficient to identify tornadic debris in a thunderstorm.
In the case of the Adairsville, GA tornado, meteorologist were able to detect a debris signature in the correlation coefficient (CC) field. The very low (blue) values of CC indicate that the signal there is not do to water or precipitation.
Using differential reflectivity to identify a hail core
In the case of severe storms, meteorologists are able to detect a hail signature in the differential reflectivity field (zdr). The slightly low (green and blue) values of ZDR indicate that the hydrometeors in that region are more spherical rather than rain drops which tend to appear more oval in shape.
Using correlation coefficient to identify the melting layer and thunderstorm updrafts
In the case of the winter weather, meteorologists can detect when ice melts to snow in the CC field. The yellow (blue) values of CC indicate that the hydrometeors are undergoing a transition as they fall to the ground. Addtionally during updrafts when liquid water is forced upward, dual-pol is able to detect a difference in the field between the ice crystals and the liquid water being forced upward.
Using specific differential phase to identify the melting layer and thunderstorm updrafts
Addtionally, meteorologists can detect when the melting layer and updrafts in the specific differential phase field. The lighter red values of KDP indicate that the hydrometeors are undergoing a phase transition as they fall to the ground or in the case of the updraft, some hyrdometeors are a different phase from the surrounding ice crystals.