Observation of MRR Tomoki Koshida Research fellow of OKI/KANAE lab 9/22’04 (Micro Rain Radar)

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