radar_basics - Weather Radar Basics RADAR Radio Detection...

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Calculus: Early Transcendental Functions
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Calculus: Early Transcendental Functions
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Weather Radar Basics
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Calculus: Early Transcendental Functions
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Chapter 3 / Exercise 74
Calculus: Early Transcendental Functions
Edwards/Larson
Expert Verified
RADAR: Radio Detection And Ranging •Developed during World War II as a method to detect the presence of ships and aircraft ( the military considered weather targets as noise ) •Since WW II, there have been many advances in radar technology (e.g., Doppler techniques) and it’s used on land, sea, and in space for both research and operational needs
Anatomy of a Weather Radar Transmitter - generates the microwave signal of the correct phase and amplitude. For a weather radar, the wavelength of the signal is ~ 10cm Antenna - the main purpose of the antenna (also called the “dish”) is to focus the transmitted power into a small beam and also to listen and collect the returned signal Feedhorn - directs the signal from the transmitter onto the antenna (also directs the return signal from the antenna to the receiver) Receiver - detects the signal returned from a target Radome - protects the antenna from high winds Transmitter Antenna Receiver Radome Feedhorn Photo by D. Zrnic
Weather Radar Scanning For a radar to find a target of interest (e.g., a cloud), 3 pieces of information are needed: Azimuth angle (direction relative to north) Elevation angle (angle above the ground) Distance to the target of interest Images on this page made available from the University of Illinois WW2010 Project
Weather Radar Scanning In meteorology, radars usually employ one of two scanning techniques: Plan Position Indicator (PPI) : The radar holds its elevation angle constant but varies its azimuth angle . If the radar rotates through 360 degrees, the scan is called a " surveillance scan ". If the radar rotates through less than 360 degrees, the scan is called a " sector scan ". Range Height Indicator (RHI ): the radar holds its azimuth angle constant but varies its elevation angle . The elevation angle normally is rotated from near the horizon to near the zenith (the point in the sky directly overhead). We are most concerned with the PPI scan. The Weather Service radars operate by collecting a series of surveillance scans at increasing elevation angles. It takes the radar ~ 5 minutes to collect the data, depending on how many elevation angles are used. The radar then repeats the cycle. Images from the University of Illinois WW2010 Project
Applications of Weather Radar: National Weather Service Radar is an important component in the arsenal of forecaster tools to understand both the current state of the atmosphere as well as what might happen in the near future. While satellite data gives a forecaster a sense of the “big picture”, radar provides more detail on at smaller scales of weather. NWS radar coverage NWS NEXRAD (KABX) Radar Reflectivity 29 September 2004 20:08 UTC NOAA GOES Visible image 29 September 2004 20:15 UTC
NWS Next Generation Weather Radar (NEXRAD) Sites •Significant improvements over older weather radar systems: •Ability to see motion of air (precipitation) using Doppler effect •Increased sensitivity and resolution allows observation of cold fronts, dry lines, and thunderstorm gust fronts The NWS currently operates 158 NEXRAD sites across the US D. Zrnic

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