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
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.
NASA/GSFC Raman Airborne Spectroscopic Lidar (RASL)
RASL
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)
Raman lidar system for the measurements of tropospheric
water vapor
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
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
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)
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
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
( ) ( ) ( ) ( ) ( )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 ==
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:
( )( )
( ) ( )( ) ( )
( )( )
( )( )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
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
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
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
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
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
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 (%)
Rotational Raman lidar for temperature measurement
Examples of return signals
Examples of results
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