Limiting Forms of Reflection and Scatter from a Surface
description
Transcript of Limiting Forms of Reflection and Scatter from a Surface
![Page 1: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/1.jpg)
specular reflector quasi-specular reflector
quasi-Lambert reflector Lambert reflector
Limiting Forms of Reflection and Scatter from a Surface
![Page 2: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/2.jpg)
![Page 3: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/3.jpg)
Doppler Radar
From Josh Wurman
NCAR S-POL DOPPLER RADAR
![Page 4: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/4.jpg)
Doppler Shift: A frequency shift that occurs in electromagneticwaves 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
![Page 5: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/5.jpg)
00 2cos tfEtE ttThe electric field of a transmitted wave
The returned electric field at some later time back at the radar 11 2cos ttfEtE tt
The time it took to travelcrt 2
Substituting:
11
22cos crtfEtE tt
The received frequency can be determined by taking the time derivative if the quantity in parentheses and dividing by 2
dtrt
tt
ttr ffcvff
dtdr
cff
crtf
dtdf
222221
1
![Page 6: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/6.jpg)
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
![Page 7: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/7.jpg)
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 oneof these three components – the motion along the beam toward or away from the radar
![Page 8: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/8.jpg)
Magnitude of the Doppler Shift
Transmitted Frequency
X band C band S band
9.37 GHz 5.62 GHz 3.0 GHzRadial velocity
1 m/s
10 m/s
50 m/s
62.5 Hz 37.5 Hz 20.0 Hz
625 Hz 375 Hz 200 Hz
3125 Hz 1876 Hz 1000 Hz
These frequency shifts are very small: for this reason, Doppler radars must employ very stable transmitters and receivers
![Page 9: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/9.jpg)
Clear-Air Radar
![Page 10: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/10.jpg)
VHFUHF10 cm
1/3
4
![Page 11: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/11.jpg)
VHFUHF10 cm
1/3
4
6 6
1
2N
i ii
n a
2nC
![Page 12: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/12.jpg)
Clear-Air Turbulence
![Page 13: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/13.jpg)
Clear-Air Wind Profilers
![Page 14: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/14.jpg)
Wind Profiler SpecificationsFrequency (MHz)
Wavelength (m)
Maximum Altitude (km)
Antenna Size (m)
Target Band Designation
50 6 20 100 x 100 Clear Air VHF
449 0.75 15 15 x 15 Clear Air and Heavy
Precipitation
UHF
915 ~0.3 5-6 5 x 5 Clear Air and
Precipitation
UHF
1036 ~0.3 5.5-6 5 x 5 Clear Air and
Precipitation
UHF
![Page 15: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/15.jpg)
915 MHz
50 MHz
![Page 16: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/16.jpg)
![Page 17: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/17.jpg)
Radial VelocityPositive TowardSurface
![Page 18: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/18.jpg)
Signal Power
![Page 19: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/19.jpg)
Bragg Diffraction (Scattering)
![Page 20: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/20.jpg)
NWS-NOAA Profiler Network
![Page 21: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/21.jpg)
SODAR
![Page 22: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/22.jpg)
SODARParameter Performance
Horizontal wind speed components Range 0-20 m/s, accuracy 0.2 m/s
Horizontal wind speed vectors Range 0 - 25 m/s
Vertical wind speed components Range 0 - 10 m/sec, accuracy 0.1 m/s
Horizontal wind Direction 0 - 359 degrees
Resolution of reading 0.1 m/s
Sampling Height 50 m - 900 m AGL
Environmental Conditions -10C to + 40C, 0 - 100% humidity
Acoustic Frequency 1525 - 2225 Hz (selectable)
Performances of ARPL SODAR
![Page 23: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/23.jpg)
Radio-Acoustic Sounding (RASS)
![Page 24: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/24.jpg)
Beam Geometry
![Page 25: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/25.jpg)
Pulsed Radar
![Page 26: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/26.jpg)
Unambiguous Range
![Page 27: Limiting Forms of Reflection and Scatter from a Surface](https://reader036.fdocuments.in/reader036/viewer/2022062310/56816703550346895ddb674d/html5/thumbnails/27.jpg)
Coherent Integration