Cool Weather Radar

[ScottM]

On Monday Tampa starts using a new weather radar system called Klystron 9. It is operated by the local cable news channel Bay News 9.

I love this about the new radar

The Klystron 9's dual-pol technology even tells meteorologists the sizes and shape of raindrops and makes the distinction between rain and ice.

That is neat and I hope this radar tech spreads around the country fast.

http://www.baynews9.com/content/36/...erful+broadcast+weather+radar+launches+Monday

 

[TMetzinger]

Dual-pol? They have a republican and a democrat?

 

[ScottM]

Dual-pol? They have a republican and a democrat?

Dual-pol short for dual polarmetric

Short overview

Dual Polarimetric
The NWS offers this explanation of Dual Polarimetric radars; "Most weather radars, such as the National Weather Service NEXRAD radar, transmit radio wave pulses that have a horizontal orientation. "Polarimetric radars (also referred to as dual-polarization radars), transmit radio wave pulses that have both horizontal and vertical orientations. The horizontal pulses essentially give a measure of the horizontal dimension of cloud (cloud water and cloud ice) and precipitation (snow, ice pellets, hail, and rain) particles while the vertical pulses essentially give a measure of the vertical dimension."

http://www.cimms.ou.edu/~schuur/dualpol/

Most weather radars, including NEXRAD, transmit and receive radio waves with a single, horizontal polarization. That is, the direction of the electric field wave crest is aligned along the horizontal axis. Polarimetric radars, on the other hand, transmit and receive both horizontal and vertical polarizations. Although there are many different ways to mix the horizontal and vertical pulses together into a transmission scheme, the most common method is to alternate between horizontal and vertical polarizations with each successive pulse. That is, first horizontal, then vertical, then horizontal, then vertical, etc. And, of course, after each transmitted pulse there is a short listening period during which the radar receives and interprets reflected signals from the cloud. Since polarimetric radars transmit and receive two polarizations of radio waves, they are sometimes referred to as dual-polarization radars. The difference between non-polarimetric and polarimetric radars is illustrated below:

Figure 2a: Non-polarimetric radars, such as NEXRAD, transmit and receive only horizontal polarization radio wave pulses. Therefore, they measure only the horizontal dimension of cloud and precipitation particles.

Figure 2b: Polarimetric radars transmit and receive both horizontal and vertical polarization radio wave pulses. Therefore, they measure both the horizontal and vertical dimensions of cloud and precipitation particles. This additional information leads to improved radar estimation of precipitation type and rate

 

[gismo]

Dual-pol short for dual polarmetric

Short overview
http://www.cimms.ou.edu/~schuur/dualpol/

I know a little bit about radar and to me that description of dual polarity is totally bogus or at least very misleading. FWIW C band radar cannot directly "measure" the size of the raindrops, the resolution cannot be significantly better than the wavelength. C band wavelengths are in the 5cm range, have you seen any 5cm raindrops? Finally, the reason that the NWS radars are S band is because that wavelength penetrates rain better than C band and thus minimizes the chances of one cell hiding another behind it. C band or X band is used by most broadcast TV radars because the antenna is much smaller for the same beamwidth.

Polarmetric (dual polarization) radar is a relatively new advancement in radar technology and does provide several benefits:

• Polarimetric radar can significantly improve the accuracy of the estimates of amounts of precipitation
• Polarimetric radar can tell the difference between very heavy rain and hail, which will improve flash flood watches and warnings
• Polarimetric radar can identify types of precipitation in winter weather forecasts, improving forecasts of liquid water equivalent or snow depth
• Polarimetric radar data is more accurate than conventional radar, saving the forecasters the step of having to verify radar data
• Increased confidence in polarimetric radar data can contribute to increased lead time in flash flood and winter weather hazard warnings

AFaIK the direct benefit of polarmetric radar is the ability to compare the vertical dimension to the horizontal dimension of the precipitation generating a return and apparently this allows for an indirect measurment of droplet size.