Saturday, June 12, 2010

The Next Generation of 'Next Generation' Radar...

In my last post I remarked that NEXRAD (NWS abbreviation for Next Generation Radar), was not perfect at estimating rainfall.  The original NEXRAD systems were launched in 1988, some 22 years ago.  Don't get me wrong, the system is far superior to its predecessors (the WSR-57 and WSR-74 radars - which offered no computer-based interpretation of data such as rainfall estimates, hail and wind shear algorithms, etc.) and has had several hardware and software upgrades since the original launch date.  My point was that you can't read a NEXRAD precipitation estimate of 3.0 inches for a given location and be 100% sure that 3.0 inches of rain fell at that location.  There will be some variance based on distance of the radar site from the area being estimated, the overall intensity and coverage of precipitation (particularly near the radar site), etc.  

The next generation of "Next Generation" radars, called a Phased Array, is currently under research and development at none other than the weather capital of the universe:  Norman, OK (home of the University of Oklahoma School of Meteorology, the National Severe Storms Laboratory (NSSL), the National Weather Center, and the Atmospheric Radar Research Center (ARRC), among other weather superstars).  
Phased Array Radar at the National Radar Testbed in Norman, OK

The Phased Array was originally developed and used by the Navy and other military outlets to detect ships, air traffic and missiles, among other things (and is still used for ths purpose today).  The Navy quickly found that the weather sometimes "interferes" with the radar's original mission of missile and aircraft hunting.  As the saying goes, one man's loss is another man's gain!

One of the downsides of NEXRAD is that it takes anywhere from 4 to 6 minutes for the radar to take a sampling of the entire environment (referred to as a volume scan) of a severe storm.  The Phased Array, on the other hand, takes less than 1 minute for a complete "volume scan".  Needless to say, the environment in and around a severe storm (particularly one that is producing or about to produce a tornado) can change quite significantly in a 6 minute period.  As a result, the much faster scanning rate of the Phased Array should result in greater lead time and warning updates on active severe weather.  In fact, it is likely that Phased Array will lead to faster, more accurate prediction of all types of weather phenomena, including severe storms, tornadoes and even rainfall and hail forecasts.  

Image taken from a PAR case study.  Note that the PAR took 29 images during the same time period that NEXRAD was only able to take 4 images of the same storm!

The Phased Array system (called PAR for short) is currently being tested actively at the NSSL's National Radar Testbed in Norman.  You can get more information, including a few case studies, related papers, and a look at the radar in action here.  The next time there is some active weather across central Oklahoma, I'll try to archive and post some images comparing the PAR data to the current NEXRAD data.

Other Links:
OU School of Meteorology
National Weather Center

1 comment:

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