Transcript Document
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Atmospheric corrections determined using Raman/backscatter lidar measurements
Valentin Mitev
Observatory of Neuchâtel
Rue de l’Observatoire 58, CH2000 Neuchâtel Switzerland Tel.: +41 –32–889 8813
E-mail: [email protected]
Atmospheric corrections determined using Raman/backscatter lidar measurements
1
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR • • • • • • • •
Content:
Measurement requirements Concept for the Lidar set-up Extinction derivation, vibrational Raman Numerical performance simulations for Extinction derivation, Raman lidar Extinction derivation, elastic backscatter Temperature derivation, pure Rotational Raman Conclusion Annex: Compact backscatter lidar in field measurements Atmospheric corrections determined using Raman/backscatter lidar measurements
2
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Measurement requirements
Zenith angle Range-resolved transmission (extinction coefficient) 0°-60°
Temperature profile Direction of probing
~7km Total transmission
Atmospheric corrections determined using Raman/backscatter lidar measurements
3
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Raman-elastic backscatter lidar – Concept:
• One laser with two/optional three separate receivers for increased dynamic range and decrease of the « blind » range • Transmitted wavelength: 355nm, 532nm, 3rd/2nd harmonics of Nd:Yag laser • Receiverd wavelengths: 355nm (elastic); 387nm (Raman N 2 ), 532nm elastic + polarisation/depolarisation; Rotational Raman at (533nm, 531nm)+ (529nm, 535nm) • • Lidar on pointing platform for collocation of the direction of probing with te line-of-sight of the Cerenkov camera; Optical&Laser part in environmental housing Atmospheric corrections determined using Raman/backscatter lidar measurements
4
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Raman backscatter lidar: Basics
• • One laser line transmitted (UV/ vis) Received Raman vibrational: N2, O2, H2O/Rorational • Determined: extinction, water vapours, temperature • Development and use: since early 1980s / in atmospheirc probing for aerosol extinction and microphysics, humidity, temperature, … Atmospheric corrections determined using Raman/backscatter lidar measurements
5
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
No. Lidar determined Value status 1 2 3 4
Extinction (355nm - 387nm) ~(total transmission 0km-7km altitude) Remark: First few hundred meters excluded
Required output Input from Lidar signal Vibrational Raman N2/Excitation 355nm Option: Rotational Raman scattering/excitation 355nm
Extinction profile 7km 12km altitude at 355nm Depolarization Ratio (355nm or 532nm) Temperature via calibrated ratio of Rotational Raman backscatter signals
Required output Elastic backscatter 355nm Vibrational Raman N2 Option: Rotational Raman /excitation 355nm Auxiliary Elastic backscatter at 355nm or 532nm with polarization analyzer Optional Rotational Raman scattering, O2 and N2, excitation 355nm Additional inputs/instruments
Molecular density, derivative
Option 1:Temperature and pressure/local dedicated radiosonde station Option 2: ECMWF+closest radiosondes station Option 3: Rotational Raman temperature measurements with dedicated lidar receiver channels
Extinction at surface level (for correction)
Surface transmissiometer
Molecular density
As above
Molecular density
As above Lidar calibration procedure
Atmospheric corrections determined using Raman/backscatter lidar measurements
6
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR 1.
Laser; 2a, 2b, 2c. Telescope long/med/short range 3a, 3b, 3c. Spectral selection 4a, 4b, 4c. Detectors 5. Pointing platform/environnmental housing 6. Synchronisation: Acqusition and Laser pulse& Main Experiment 7.Signal acquisition electronics
6 7 Data out Synch out 5 4a 4b 3b 4c 3a 3c 1 2a 2b 2c
Atmospheric corrections determined using Raman/backscatter lidar measurements
7
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Laser
532nm, 355nm
Receiver
532nm-
s
4
532nm -
p
3
387nm 532nm
2 2 1 3
532nm (e) 355nm (e) 356/8nm (2*RR-S) 352/4nm (2*RR-aS)
355nm RR1…RR4
5
aS1/ aS2/ 355nm/ S1/ S2 1-Coupling optics 2-Dichroic beamsplitter 3-Interference filter 4-Depolarisation beamsplitter 5-Grating spectrometer
Atmospheric corrections determined using Raman/backscatter lidar measurements
8
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Extinction derivation from vibrational Raman backscatter
E
R
( r )
R ( r )
E
L
K
R
O ( r A ) r
2
c 2
N M ( r )
d
Ram d
( v )
R
( r ) exp
0
r
( r ' )
R
( r ' )
dr '
… two times the averaged value of the extinction coefficient in the spectral range 355nm – 387nm
d dr
ln
N N 2 ( r ) / S N 2 ( r )
( r )
N 2 ( r )
Atmospheric corrections determined using Raman/backscatter lidar measurements
9
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR • • • • • • • • •
Inputs for the performance simulations:
Lidar subsystems specifications Pulse energy at 355nm: 300mJ/PRR : 20Hz Telescope diameter of the « long-range » receiver: 80cm Efficiency transmitter/receiver (without filter): 07./07 Transmission, filter: 0.6
Detector, Quantum efficiency: 0.2
Lidar measurement parameters Integration time: 600sec Zenith angle (from zenith): 60 ° Range resolution: 120m at 60 Ambient optical background: full moon – 7*10 -4 Wm -2
m
m -1 Atmospheric corrections determined using Raman/backscatter lidar measurements
10
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Atmosphere: • Molecular model: hydrostatic • Aerosol model: PBL/dust, 0 - 2 km tropospheric layer, 3 - 5km cirrus cloud, 9 - 10,4km
Cirrus cloud, 9 – 10.4km
Tropopsphere/Desert Dust, 3-5km PBL/Dust layer, 0-2km
Atmospheric corrections determined using Raman/backscatter lidar measurements
11
HEAPnet meeting, 19-20 February 2007, Amsterdam
Vibrational -Raman signal – simulated, at slant path 60 deg LIDAR Atmospheric corrections determined using Raman/backscatter lidar measurements
12
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Extinction from the vibrational Raman signal Atmospheric corrections determined using Raman/backscatter lidar measurements
13
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Error of the extinction coefficient obtained from the vibrational Raman signal Atmospheric corrections determined using Raman/backscatter lidar measurements
14
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Error of the extinction coefficient obtained from the vibrational Raman signal - ZOOM
Range x10
4
m , @60° zenith angle
Atmospheric corrections determined using Raman/backscatter lidar measurements
15
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Total atmospheric transmission of the marked layers, derived from the simulated Raman signal « TRmod » = model value; « TRmeas » = derived value
Cirrus cloud
TRmodcloud = 0.9498
TRmeas cloud = 0.9508
TRmodel = 0.5836
TRmeasured = 0.5830
Tropopsphere/Desert Dust PBL/Dust layer
Atmospheric corrections determined using Raman/backscatter lidar measurements
16
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Concept for derivation of the extinction coefficient inside aerosol layer using elastic backscatter
Assumptions: - The layer contains the same type of aerosol (e.g.,subvisible cirrus cloud)
-
Aerisol-free atmosphere above the cloud
-
Total layer (cloud) transmision is determined from the Raman signal Atmospheric corrections determined using Raman/backscatter lidar measurements
17
HEAPnet meeting, 19-20 February 2007, Amsterdam
Extinction from Elastic backscatter signal - simultion LIDAR Aerosol layer (Cirrus cloud) reference Atmospheric corrections determined using Raman/backscatter lidar measurements
18
LIDAR
HEAPnet meeting, 19-20 February 2007, Amsterdam
The elastic-backscatter lidar equation
E
( r )
E
L
K
O ( r A ) r
2
c
2
( r ) exp
2
r 0
( r ' ) dr '
S ( r )
E
( r ) r 2
dS
( r ) dr
1
d
dr
2
Atmospheric corrections determined using Raman/backscatter lidar measurements
19
LIDAR
HEAPnet meeting, 19-20 February 2007, Amsterdam
The Fernald's inversion method for derivation of the backscatter coefficient;
is omitted
S ( r ) exp
2 ( lr
lr 0 ) rf
r d r
mol ( r
)
S
( r r f
)
2 lr r f
r d r
S ( r
) exp
2 ( lr
lr 0 ) r f
r d r
mol ( r
)
( r )
mol
( r )
aer
( r )
Additional conditions: • “ lr ” is constant (extinction to backscatter ratio, initial approximation taken from model values, here the depolarization ratio may help to classify the cloud particles), • “ r f ” is a reference range
• “
(r f )
” is known ( typically, the molecular backscatter) Atmospheric corrections determined using Raman/backscatter lidar measurements
20
LIDAR
HEAPnet meeting, 19-20 February 2007, Amsterdam
Assuming: “
(r)
” is derived from elastic lidar
Total double trip transmission “DT” is derived from Raman lidar,
Molecular backscatter is known/type of particles may be “guessed”
Then we may determine “ lr ” from DT ( r 1 , r 2 )
exp
2 r
2
lr .
r 1 aer ( r ' )
mol ( r '
) dr '
And the profile of the aerosol extinction in the cloud
aer
( r )
lr .
aer
( r )
Atmospheric corrections determined using Raman/backscatter lidar measurements
21
HEAPnet meeting, 19-20 February 2007, Amsterdam
Derivation of the atmospheric temperature profile using pure rotational Raman backscatter LIDAR Rotational Raman Spectra of N2 and O2, Excitation at 532nm Atmospheric corrections determined using Raman/backscatter lidar measurements
22
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Spectral intervals in pure RR where the scattering cross-sections derivative has opposite sign
of N2 (red) and O2 (black)
lines of N2 (red) and O2 (black)
R ( T K )
I I
N
N 2 st ( T 2 st ( T )
)
I I
N
N 2 ast ( T 2 ast ( T )
)
I I
O
O 2 st 2 st ( ( T T )
)
I I
O
O 2 ast 2 ast ( T ( T ) )
3,5 3 2,5 2 1,5 1
« - » « - »
0,5 0 -0,5 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 -1
« + » wavelength, nm « + »
exp( a
b / T )
R(T)=exp( Typically
is critical.
– dR/dT ~0.05%
/T)
A calibration of the lidar
Atmospheric corrections determined using Raman/backscatter lidar measurements
23
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR Atmospheric corrections determined using Raman/backscatter lidar measurements
24
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Uncertainty - ZOOM 60° zenith angle Integration time: 30min Range resolution: 120m
Atmospheric corrections determined using Raman/backscatter lidar measurements
25
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Summary:
A Raman-backscatter Lidar for CTA-site is a technically feasible solution for the requirements in CTA: • Advantages: « Real time » and « Real direction » coinciding • with the pointing direction the Cherenkov Telescope(s) The necessary lidar methods and algorithms are developed, • adaptation to the tasks will be possible ; Realistic subsystem specifications, compatible with the • commercially available hardware; Additional /Optional lidar tasks: laser backscatter for calibration of the Cherenkov telescope; Remark: This presentation is not with system optimisation. The final specifications may be different from the specifications used for numerical simulations Atmospheric corrections determined using Raman/backscatter lidar measurements
26
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Next step for the Raman lidar - a design study with the following objectives:
• Detailed numerical simulations of the various detection modes with respect to the finalised detection requirements • • Concept design and optimisation; Algorithm developments; • power Optional 1: Participation in atmospheric characterisation at • the potential CTA sites; Optional 2: Raman lidar bread-board/ lower aperture and Atmospheric corrections determined using Raman/backscatter lidar measurements
27
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
ANNEX:
Possibility for atmospheric characterisation at potential CTA sites with a compact elastic backscatter lidars
3.5
3.0
r] 8 5:0 0-1 :5 14 0, 00 9.2
.0
13 n: riso pa rcom nte burg l I) Ham châte MP stitut ( de Neu oire lanck-In vat -P Obser Max L-up Lidar MA ET - I LIN EAR m*s -6 [1/ 2.5
10 ent * 2.0
fici 1.5
coef ing 1.0
scatter 0.5
osol back Aer 0.0
7000 6000 5000 4000 3000 2000 1000 0 -0.5
00 -10
Atmospheric corrections determined using Raman/backscatter lidar measurements
28
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Micro-pulse lidars on stratospheric aircraft (M55)
MAL 1 MAL 2 32 cm MAL-1 MAL-2
Atmospheric corrections determined using Raman/backscatter lidar measurements
29
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Micro-pulse lidars on stratospheric aircraft (M55)
SCOUT O3/ Brunei Darwin, 12 November 2005
Backscatter Ratio=
(
a +
m )/
m
Atmospheric corrections determined using Raman/backscatter lidar measurements
30
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR • Ground-based LIDAR, transportable development, observations, data analysis
Example for 24h- measurement of the aerosol load above Basel in project BUBBLE
600mmx600mmx700mm
The lidar on the balcony of the 5th floor of the University of Basel; Project BUBBLE (2001-2002) . The lidar was remotely operated from ON
Atmospheric corrections determined using Raman/backscatter lidar measurements
31
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR • Ground-based three-wavelength elastic Raman LIDAR, in Observatory of Neuchatel Operational, Presently under refurbishment Concerning the CTA-activity: • Not transportable • May be a base for the Raman lidar bread board/test bench wrt the CTA requirements • Possibility to be deployed on site (with limitations for steering, schedule …) Atmospheric corrections determined using Raman/backscatter lidar measurements
32
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Summary
for the “compact lidar” capabilities:
-
Possibility for qualitative characterisation of the aerosol vertical/slant path profile: Backscatter coefficient profile (~30% uncertainty, systematic), altitude of layers,
-
Convenient transportation and implementation on the field
-
Limitations: The qualitative evaluation is not adequate to the requirements in CTI, i.e., NOT a replacement for the Raman lidar) Atmospheric corrections determined using Raman/backscatter lidar measurements
33
HEAPnet meeting, 19-20 February 2007, Amsterdam
LIDAR
Thank you!
Valentin Mitev
([email protected]) Observatory of Neuchâtel
Rue de l’Observatoire 58, CH2000 Neuchâtel Switzerland
Atmospheric corrections determined using Raman/backscatter lidar measurements
34