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Specular reflectorquasi-specular reflector quasi-Lambert reflector Lambert reflector Limiting Forms of Reflection and Scatter from a Surface.

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Presentation on theme: "Specular reflectorquasi-specular reflector quasi-Lambert reflector Lambert reflector Limiting Forms of Reflection and Scatter from a Surface."— Presentation transcript:

1 specular reflectorquasi-specular reflector quasi-Lambert reflector Lambert reflector Limiting Forms of Reflection and Scatter from a Surface

2 Bragg Diffraction (Scattering)

3 Pulsed Radar

4 Doppler Radar From Josh Wurman NCAR S-POL DOPPLER RADAR

5 Doppler Shift: A frequency shift that occurs in electromagnetic waves due to the motion of scatterers toward or away from the observer. Doppler radar: A radar that can determine the frequency shift through measurement of the phase change that occurs in electromagnetic waves during a series of pulses. Analogy: The Doppler shift for sound waves is the frequency shift that occurs as race cars approach and then recede from a stationary observer

6 The electric field of a transmitted wave The returned electric field at some later time back at the radar The time it took to travel Substituting: The received frequency can be determined by taking the time derivative if the quantity in parentheses and dividing by 2 

7 Sign conventions The Doppler frequency is negative (lower frequency, red shift) for objects receding from the radar The Doppler frequency is positive (higher frequency, blue shift) for objects approaching the radar These “color” shift conventions are typically also used on radar displays of Doppler velocity Blue: Toward radar Red: Receding from radar

8 Note that Doppler radars are only sensitive to the radial motion of objects Air motion is a three dimensional vector: A Doppler radar can only measure one of these three components – the motion along the beam toward or away from the radar

9 Clear-Air Radar

10 VHF UHF 10 cm

11 Clear-Air Turbulence

12 Clear-Air Wind Profilers

13 Wind Profiler Specifications Frequency (MHz) Wavelength (m) Maximum Altitude (km) Antenna Size (m) TargetBand Designation x 100Clear AirVHF x 15Clear Air and Heavy Precipitation UHF 915~ x 5Clear Air and Precipitation UHF 1036~ x 5Clear Air and Precipitation UHF

14 915 MHz 50 MHz

15

16 Radial Velocity Positive Toward Surface

17 Signal Power

18 NWS-NOAA Profiler Network

19 Beam Geometry

20 Unambiguous Range

21 Coherent Integration


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