Question: What do meteorologists, police and television baseball announcers have in common? Answer: Doppler radar, for one thing.
Radar, RAdio Detection And Ranging, uses a pulse of microwave energy sent out and echoed back by a distant target. Using radar, we can spot targets at various distances and directions. Tracking airplanes was the first goal of radars. Meteorologists have long used radar to spot the locations, intensities and movements of precipitation that are associated with storm systems. Recently the National Weather Service installed a network of new radar units across the U.S. that can also detect motions of raindrops, snowflakes, and hail using the Doppler principle. When a moving target echoes back part of the radar pulse, the frequency of the electromagnetic energy is shifted slightly from the original signal value. The amount of shift relates to the speed of target movement directly toward or away from the receiver. With a weather radar this means we can infer the wind speeds and directions that move the raindrops and other particles in the storm.
Police agencies have also used Doppler radar units in enforcing speed limits. A traffic radar aimed at a moving car will tell the car's speed directly toward or away from the unit. The sports media have been quick to use this technology to impress viewers with the speed of a baseball pitch or tennis serve. While the speed of a pitch from the mound to home plate can be "measured" because it travels toward the radar, a throw from third to first base would not because it is moving across the radar beam. So Doppler weather radar interpretation is much more complex than baseball and chasing speeders. Storm motions are scanned across the entire atmosphere surrounding the radar site for hundreds of kilometers out and several kilometers up, with no "seventh inning stretch"!
Another additional feature of the new Doppler radar units operated by the National Weather Service is the capability to estimate the accumulated rainfall over a given area near the radar unit and then alert the radar operator to the possibility of flooding if some critical threshold were reached. As a result, flash flood watches and warnings can be issued more promptly.
For more information describing interpretation of DataStreme radar summary products, you may consult Thursday's electronic Supplemental Summary Information .
To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 7 Chapter Progress Response Form, under section B. Daily Summary.