lecture 9: raman lidar - ustcstaff.ustc.edu.cn/~litao/ors9_v2.ppt.pdf · lecture 9: raman lidar...
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Lecture 9: Raman lidar
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Water vapor mixing ratio measured by the SRL during the dryline event. Temporal resolution is 3 minutes, vertical smoothing varied between 90 meters at 0.5 km to 330 meters above 4 km.The calibration of the data was determined with respect to SuomiNet GPS mounted on the SRL trailer.
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NASA/GSFC Raman Airborne Spectroscopic Lidar (RASL)
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RASL
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RASL Specifications
Laser Continuum 9050 Nd:YAG (355 nm), 350 mj/pulse, 50 Hz
Telescope Custom 24” athermal, manufactured by DFM Engineering
Data acquisition 250 Mhz photon counting and 20 Mhz analog detection
Range resolution 7.5 meter
Measurements [Molecule/
Wavelength (nm)/Bandpass (nm)]
water vapor/407.5/0.25
liquid water/403.2/6.0
nitrogen/386.7/0.3
oxygen/375/0.3 or CO2/371.6/0.3
elastic unpolarized/354.7/0.3
elastic parallel polarized/354.7/0.3
elastic perpendicular polarized/354.7/0.3
Detectors Hamamatsu R1924 (Raman) and R7400 (aerosol) PMTs
Field of View 0.25 mrad
NASA/GSFC Raman Airborne Spectroscopic Lidar (RASL)
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Raman lidar system for the measurements of tropospheric
water vapor
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0.625mCassegraintelescope
PMT
407.8nm
Amplifier
PMT Amplifier
PMT Amplifier
386.7nm
355nm
T
D
R
LASER
MCS1
MCS2
MCS3
355nm PD
SynchronizationControl
Electronic gatecontrol signal
Trigger signal
ControlComputer
Ocular
FieldStop
F1
F2
F3
407.8nm386.7nm355nm
Laser control signal
Raman Lidar System
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Main technical parameters of Raman Lidar System Laser Nd:YAG Wavelength (nm) 355 Pulse energy (mJ) 80 Pulse width (ns) 20 Beam divergence (mrad) ≤ 1
Pulse repetition (Hz) 10 Receiving telescope Cassegrain Diameter (mm) 625 Filed of view (mrad) 3 Interference filters Central wavelength (nm) 407.8 386.7 355 Bandwidth (nm) 4.7 4.3 1 Transmission (%) 55 60 40 PMT(EMI) 9214QB×2 9817B
Preamplifier(EG&G) VT120×3
Gain 200 Bandwidth (MHz) 350 Multi-channel Scaler EG&G 914P×3
Maximum count rate 150MHz
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Characteristics of three dichronic beam splitter
Beam Splitter 407.8nm 386.7nm 355nm
T >95%(R) 15%(R) 85%(T)
>85%(T)
D 65 %(R) 35%(T)
>85%(T)
R >95%(R) >85%(R)
350 360 370 380 390 400 410 4200
10
20
30
40
50
60
70
80
90
100
Trichronic
Tran
smiss
ion
(%)
Wavelength (nm)350 360 370 380 390 400 410 4200
10
20
30
40
50
60
70
80
90
100
DichronicTr
ansm
issio
n (%
)
Wavelength (nm)350 360 370 380 390 400 410 4200
10
20
30
40
50
60
70
80
90
100
Reflector
Tran
smiss
ion
(%)
Wavelength (nm)
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Raman Water Vapor
Raman Nitrogen
Rayleigh-Mie
Central wavelength (nm) 407.8 386.7 355 Bandwidth (nm) 4.7 4.3 1 Transmission at Central Wavelength (%)
55 60 40
Transmission at 355nm and 532nm
10-12 10-12
Transmission at 200nm~1200nm
10-6 10-6 10-5
Transmission at 375nm, 387nm, 580nm and 607nm
10-8
Diameter (mm) 25.4 25.4 25.4 Thickness (mm) 10 9 5
Characteristics of three interference filters
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400 405 410 415 4200
10
20
30
40
50
60
70
80
90
100
Raman water vapor filter
Tran
smis
sion
(%)
Wavelength (nm)375 380 385 390 395
0
10
20
30
40
50
60
70
80
90
100
Raman nitrogen filter
Tran
smiss
ion
(%)
Wavelength (nm)
Transmission function of two Raman interference filters
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( ) ( ) ( ) ( ) ( )z,z,qz,z,qznzk
zS HHHH
H 0002 λλπσλλ =
Raman Lidar Equation
Raman Water Vapor:
Raman Nitrogen:
( ) ( ) ( ) ( ) ( )z,z,qz,z,qznzk
zS NNNN
N 0002 λλπσλλ =
Water Vapor Mixing Ratio:
( ) ( )( )
( )( )
( )( )znzn
MM
znzn
MM
znznzw
dry
N
dry
H
N
H
dry
H
dry
H ==
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where Cw is the system calibration constant ( )
( ) dry
N
dry
H
H
N
H
Nw n
nMM
kkC
πσπσ
=
( )z,z0wqΔ is the transmission correction function
( ) ( )( )z,z,q
z,z,qz,z0H
0N0
wq λ
λΔ =
( ) ( ) ( )( )zSzSz,zCzw
N
Hwqw 0Δ=
Water Vapor Mixing Ratio:
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( )( )
( ) ( )( ) ( )
( )( )
( )( )zz
zSzS
zzSzzS
zSzS
H
N
N
H
NN
HH
N
H
γγ
γγ
⋅==''
/'/'
( )( )zz
H
N
γ
γ
can be obtained through simultaneously measuring the return signals at 386.7nm for Raman water vapor and nitrogen channels.
Retrieval for signals within the overlap region ( )( )z'Sz'S
N
H
0.0 0.5 1.0 1.5 2.0 2.5 3.01.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
May.19,1999 Jun.02,1999
Altitude(km)
γγΝΝ // γγ
ΗΗ
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0.80 0.85 0.90 0.95 1.000
1
2
3
4
5
6
532nm τ=0.0 τ=0.25 τ=0.5 τ=1.0
Altit
ude(
km)
Transmission RatioVertical profiles of the transmission correction function for different aerosol optical depth
Transmission Correction Function ( )z,z0wqΔ
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30
35
40
45
50
55
60 The mean calibration constant
C--w=41.59
The standard deviation of calibration constant δδCw=2.56
May.10 15 20 25 30 Jun.05 10 15 20
Cw
Date
Calibration Constant Cw
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0 1 2 3 4 5 6 7 80
1
2
3
4
5 Lidar radiosonde 20% Relative humidity
May 6,1999
Alti
tude
(km
)
Water vapor mixing ratio (g/kg)0 1 2 3 4 5 6 7 8 9 10
0
1
2
3
4
5
Lidar radiosonde 20% Relative humidity
May 11,1999
Alti
tude
(km
)
Water vapor mixing ratio (g/kg)
0 2 4 6 8 10 120
1
2
3
4
5
Lidar radiosonde 20% Relative humidity
May 14,1999
Alti
tude
(km
)
Water vapor mixing ratio (g/kg)
Vertical Profiles of the water vapor mixing ratio
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0 1 2 3 4 5 6 7 80
1
2
3
4
5 May 26, 1999 20:24-20:33 20:33-20:41 20:41-20:50 20:50-21:00 21:00-21:09 21:09-21:18
Alti
tude
(km
)
water vapor mixing ratio (g/kg)
Spatial and temporal variation of water vapor
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0 2 4 6 8 10 12 14 16 18 20 220
1
2
3
4
5
6 Lidar radiosonde 100% relative humidity 355nm
Jun.02,1999
Alti
tude
(km
)
Water vapor mixing ratio (g/kg)
Water vapor mixing ratio in the cloud
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Error Analysis
2222
⎟⎟⎠
⎞⎜⎜⎝
⎛+⎟
⎠
⎞⎜⎝
⎛+⎟⎠
⎞⎜⎝
⎛=⎟⎠
⎞⎜⎝
⎛
w
w
CC
TT
SS
ww δδδδ
0 10 20 30 40 501.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Jun.02,1999
Altitude(km)
δδS/S(%)0 2 4 6 8 10
0
1
2
3
4
5
6
Altit
ude(
km)
δT/T (%)
0 10 20 30 40 501.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Jun.02,1999
Alti
tude
(km
)
δδw/w (%)
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Rotational Raman lidar for temperature measurement
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Examples of return signals
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Examples of results