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Observation of MRR
Tomoki Koshida
Research fellow of OKI/KANAE lab9/22’04
(Micro Rain Radar)
Today’s 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
Schematic graph of radar
小倉義光「一般気象学」より
MRR observation
MRR observation
MRR observation
Observation sample
• Time heightcross sectionof radar reflectivity
Observation sample2
• Time height cross section of Doppler speed
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
How to analyze
Radar reflectivity
Doppler speed
小倉義光「一般気象学」より
Property of Radar reflectivity• Radar reflectivity Z is proportional to the di
ameter D of raindrop to the sixth power.
• Radar reflectivity of Water(rain) is the larger than that of Ice(snow)
6DZ
Summary one
• MRR observe radar reflectivity of rain vertically.
• MRR observe Doppler speed of falling rain vertically.
The observing parameters
• What is observed?F0
0
F05
F10
F15
F20
F25
F30
F35
F40
F45
F50
F55
F60 200
1200
2200
3200
4200
5200
ドップラー速度
(m)高度
2004/ 6/ 21 15:51:00スペクトル単位体積散乱断面積の表示- 100- - 90 - 90- - 80 - 80- - 70 - 70- - 60 - 60- - 50 - 50- - 40
The number concentration
0.25
0.44
0.66
0.92
1.21
1.58
2.04
2.69
3.77
200
1200
2200
3200
4200
5200
数濃度10̂ #/ m3/ mm
( mm)雨滴粒径直径
(m)高度
MRR 2004/ 6/ 21 15:51:00で観測された粒径分布- 3- - 2 - 2- - 1 - 1- 0 0- 1 1- 22- 3 3- 4 4- 5 5- 6 6- 7
Rain fall rate
• If you want to know rain rate,
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
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
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
Radar equation(1)
• Transmitting power : PtPt/4πR2
R
Radar equation(2) – antenna gain
• If you use antenna, you can concentrate energy : G transmitting power per unit area is Pt*G/4πR2
R
Radar equation(3) – effective cross section
• If target area is At and effective cross section is Ae, you can receive the power : Pr
R
424Pr
r
AeAtGPt
Radar equation(4) – effective cross section2
• From antenna theory G and Ae have following relation
R
43
22
4Pr
r
AtGPt
2
4
Ae
G
Radar equation(5)- back scattering cross section
• if energy is reflected equally(ideally), back scattering cross section is At.
The energy of incidence
The energy of reflection
area At(m2)
The energy of reflection
area σ(m2)
ideal area At(m2)
Unknown material σ(m2)
Radar equation(6) – single target
43
22
4Pr
r
GPt i
n
ii
r
GPt
143
22
4Pr
Radar equation – multi target
Scattering cross section per volume
• Now introduce new parameter
n
iiV 1
1
dv
r
rrGPt
oV
4
2
3
2 )()(
4Pr
dvr
rGPt
oV4
2
3
2 )(
64Pr
Physical property of η
• Radar reflectivity for raindrop
• Rain drops are scattering equally in observing volume
• => the back scattering cross section of each drop
Radar equation(7) typical
2
0 0
223
2
sin),(64
Pr ddGr
Pt
2Pr
rC
Radar observation schematics
Calculate distance
• Pulse radar calculate distance from time
Pulse radar and CW radar
• Pulse radar
• CW radar (continuous wave)
timeTra
nsm
it
pow
er
timeTra
nsm
it
pow
er
2 μs 4msReceiving time tells distance
FMCW radar(1)
schematic graph of FMCW signal
time(sec)
freq
uenc
y(1/
s)
trans_frequency receive_frequency_near
FMCW radar(1)
schematic graph of FMCW signal
time(sec)
freq
uenc
y(1/
s)
trans_frequency receive_frequency_near
schematic graph of FMCW signal
time(sec)
freq
uenc
y(1/
s)
trans_frequency receive_frequency_far
FMCW radar(2)
Stationary target
Moving target(1)schematic graph of FMCW signal
time(sec)
freq
uenc
y(1/
s)
trans_frequencyreceive_frequency_stationary targetreceive_frequency_moving target (Doppler)
Moving target(2)
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
2
),(),Pr(
h
hCh
sm /97.878.0
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
Z-R relation
RBZ Z:radar reflectivity index(mm6/m3), almost the same η the radar reflectivity
R:rain fall rate, the depth of rain per one hour (mm/h)
B,β: conversion parameters which differs rain by rain
Drop size distributionaveraged over rain type
平均的な降水タイプ別の粒径分布
0.0010.01
0.11
10100
100010000
0 1 2 3 4 5
(mm)粒径
(m-3
mm
-1)
数密度
・
前線 低気圧 台風Frontal : cyclone : typhoon
The first task
• Comparison between MRR and disdrometer at the ground
• And to know MRR character of observation about rain drop size distribution
Comparison between MRR and rain gauge (TE525)
comparison between Tipping buket and MRR-2(2004/ 06 except6/ 21)
0.01
0.1
1
10
100
0.01 0.1 1 10 100
rainfall rate buket(mm/ h)<10min observation maltipled by 6 >
rain
fall
rate
MR
R-2
(mm
/h)
<av
erag
ed o
ver
10m
in>
Comparison between MRR and disdrometer(RD80)
comparison between RD80 and MRR-2(2004/ 06 except6/ 21)
0.01
0.1
1
10
100
0.01 0.1 1 10 100
rainfall rate RD80(mm/ h)<averaged over 10min>
rain
fall
rate
MR
R-2
(mm
/h)
<av
erag
ed o
ver
10m
in>
Comparison between RD80 and TE525
comparison between Tipping buket and RD80(2004/ 06 except6/ 21)
0.01
0.1
1
10
100
0.01 0.1 1 10 100
rainfall rate buket(mm/ h)<10min observation maltipled by 6 >
rain
fall
rate
RD
80(m
m/h
) <
aver
aged
ove
r 10
min
>
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
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
Reflectivity of rain drops
0.1
1
10
100
1000
0 1 2 3 4 5drop size(mm)
rada
r re
flect
ivity
spec
trum
mm
6/m
3/m
m)
(Ze_MRR(D)Ze_DR80(D)Z_Marshall- Palmer(2mm/ h)
Marshall & Palmer
)(*)(25
4
DDND
Zb
)**1.4exp()( 21.00 DRnDN
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
Difference between Rayleigh and Mie
スペクトル強度の違い
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5(mm)粒径
スペクトル反射強度
(mm
6/m
3/m
m)
rayleighスペクトル反射強度 mieスペクトル反射強度
Summary three
• MRR tends to overestimate
• Overestimate occurred at large drop size area
• My task is half way…..
Than you for your attention