Likewise, as the train moves away from you, the sound waves are stretched, lowering the pitch of the whistle. As the train approaches, the sound waves that make up the whistle are compressed making the pitch higher than if the train was stationary. You have most likely experienced the "Doppler effect" around trains.Īs a train passes your location, you may have noticed the pitch in the train's whistle changing from high to low. This Doppler effect was named after the Austrian physicist, Christian Doppler, who discovered it. The phase of the returning signal typically changes based upon the motion of the raindrops (or bugs, dust, etc.). The ability to detect the "shift in the phase" of the pulse of energy makes NEXRAD a Doppler radar. Learn about the different scanning modes of the Radar here
The remaining 59 minutes and 53 seconds are spent listening for any returned signals. When the time of all the pulses each hour are totaled (the time the radar is actually transmitting), the radar is "on" for about 7 seconds each hour. NEXRAD spends the vast amount of time "listening" for returning signals it sent. This process of emitting a signal, listening for any returned signal, then emitting the next signal, takes place very fast, up to around 1300 times each second! Computers analyze the strength of the returned pulse, time it took to travel to the object and back, and phase, or doppler shift of the pulse. This reflected signal is then received by the radar during its listening period. Note: it's a small fraction of the emitted energy that is scattered directly back toward the radar. If the energy strikes an object (rain drop, snowflake, hail, bug, bird, etc), the energy is scattered in all directions (blue). The radar emits a burst of energy (green in the animated image). Gulwani said the tree hit the roof and front bedroom but they're still trying to assess the damage.NEXRAD (Next Generation Radar) obtains weather information (precipitation and wind) based upon returned energy. "I started calling the village so they can help us out." "We were shocked, we came out and we said what is this because we didn't have a clue," said Murad Gulwani. The homeowners said they were coming home dinner when they saw the fallen tree. Morton Grove police and fire officials responded to a large tree that fell onto a home in the 5500 block of Lake Street. "We've gotten some downpours this summer but nothing like this," said Jeff Mayburn who lives in Morton Grove. Officials are still doing survey work in Kendall and Grundy counties. In Will County, an EF-1 tornado touched down from Minooka to Shorewood and an EF-0 tornado touched down from central Minooka to the Des Plaines River. In Kankakee County, an EF-0 tornado touched down on the west side of Kankakee, and an EF-1 tornado touched down in the town of Momence. The National Weather Service said they have confirmed four tornadoes in the south suburbs from Friday night. Severe weather caused damage across the north and northwest suburbs in the Chicagoland area Friday into Saturday morning.ĬHICAGO (WLS) - Severe weather caused damage across the north and northwest suburbs in the Chicagoland area Friday into Saturday morning.
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