Observation%20of%20MRR

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Observation of MRR
(Micro Rain Radar)

• Tomoki Koshida
• Research fellow of OKI/KANAE lab
• 9/2204

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Todays topic

• The sample of MRR observation- what we can
  observe?
• The basic of radar observation- how we can
  observe?
• The object of MRR observation- my interest

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Schematic graph of radar
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MRR observation
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MRR observation
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MRR observation
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Observation sample

• Time heightcross sectionof radar reflectivity

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Observation sample2

• Time height cross section of Doppler speed

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Vertical profile(2004/4/2)

• Vertical axisheight(m)
• Horizontal axisrain rate(mm/h) orspeed(m/s)
• Black rain ratered Doppler speed

Layer 1
Layer 2
Layer 3
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How to analyze
Radar reflectivity
Doppler speed
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Property of Radar reflectivity

• Radar reflectivity Z is proportional to the
  diameter D of raindrop to the sixth power.
• Radar reflectivity of Water(rain) is the larger
  than that of Ice(snow)

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Summary one

• MRR observe radar reflectivity of rain
  vertically.
• MRR observe Doppler speed of falling rain
  vertically.

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The observing parameters

• What is observed?

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The number concentration
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Rain fall rate

• If you want to know rain rate,

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Summary one-prime

• MRR observes the back scattering cross section
  per unit per Doppler speed
• Doppler speed is converted to the diameter of
  rain drop D
• The back scattering cross section is converted to
  the number concentration N(D)
• Rain fall rate can be calculated above two
  parameters

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MRR physical Basis

• Basis of Radar observation
• History of Radar observation to rain
• Radar equation
• scattering
• Difference of MRR and standard radar system
• Pulse radar vs. CW (continuous wave) radar
• Doppler radar vs. (ordinary) radar

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The history of radar observation

• Radar radio detection and ranging
• To find the enemy airplane or battleship
• rain as noise but if heavy rain cause strong
  echo then you can measure the rain fall rate

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Radar equation(1)

• Transmitting power PtPt/4pR2

R
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Radar equation(2) antenna gain

• If you use antenna, you can concentrate energy
  G transmitting power per unit area is
  PtG/4pR2

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Radar equation(3) effective cross section

• If target area is At and effective cross section
  is Ae, you can receive the power Pr

R
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Radar equation(4) effective cross section2

• From antenna theory G and Ae have following
  relation

R
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Radar equation(5)- back scattering cross section

• if energy is reflected equally(ideally), back
  scattering cross section is At.

area s(m2)
ideal area At(m2)
Unknown material s(m2)
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Radar equation(6) single target
Radar equation multi target
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Scattering cross section per volume

• Now introduce new parameter

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Physical property of ?

• Radar reflectivity for raindrop
• Rain drops are scattering equally in observing
  volume
• gt the back scattering cross section of each drop
  

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Radar equation(7) typical
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Radar observation schematics
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Calculate distance

• Pulse radar calculate distance from time

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Pulse radar and CW radar
2 µs
4ms
Receiving time tells distance

• Pulse radar
• CW radar (continuous wave)

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FMCW radar(1)
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FMCW radar(1)
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FMCW radar(2)
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Stationary target
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Moving target(1)
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Moving target(2)
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Summary two

• FMCW radar basically use the same radar equation
  of other radar
• MRR observes 29 levels of height by using
  frequency modulation
• Observing range are limited Doppler speed

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Example of analysis

• My interestis to know the rain drop size
  distribution in the air
• Radar system calculate rain fall rate using Z-R
  relation

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Z-R relation
Zradar reflectivity index(mm6/m3), almost the
same ? the radar reflectivity Rrain fall rate,
the depth of rain per one hour (mm/h) B,ßconversi
on parameters which differs rain by rain
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Drop size distributionaveraged over rain type
Frontal cyclone typhoon
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The first task

• Comparison between MRR and disdrometer at the
  ground
• And to know MRR character of observation about
  rain drop size distribution

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Comparison between MRR and rain gauge (TE525)
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Comparison between MRR and disdrometer(RD80)
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Comparison between RD80 and TE525
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Summary of accuracy
comparison Total rain ratio correlation
RD80 MRR MRR/RD801.54 0.97
TE525 MRR MRR/TE5251.54 0.96
TE525 RD80 RD80/TE525 0.99 0.97
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Comparison of rain drop size distribution

• MRR and RD80 observe the rain drop size
  distribution
• We can calculate of radar reflectivity of rain
  drop size spectrum

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Reflectivity of rain drops
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Marshall Palmer
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Rayleigh approximation Scattering

• We assume the rain drop size smaller than 1/10 of
  wave length
• MRR use 12.4mm wave length
• Calculate the difference of Rayleigh and Mie

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Difference between Rayleigh and Mie
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Summary three

• MRR tends to overestimate
• Overestimate occurred at large drop size area
• My task is half way..

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Than you for your attention