Comparing various Lidar/Radar inversion strategies using Raman Lidar data (part II)
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Comparing various Lidar/Radar inversion strategies using Raman Lidar data (part II)D.Donovan, G-J Zadelhof (KNMI)
Z. Wang (NASA/GSFC)
D. Whiteman (NASA/GSFC)
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Cnet October Delft
Background/Rational Raman-vs-Elastic backscatter lidars Results Summary
Introduction
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Cnet October Delft
Active (lidar/radar) cloud remote sensing
LidarLidar
Radar
Returned Power
Tim
e or
R
ange
Lidar Radar
Difference in returns is a function of particle size !!
350-1100nm
3-100mm
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Cnet October Delft
Rational KNMI lidar/radar routine developed for simple
elastic lR backscatter lidar. No Rayleigh return MPL lidar data from ARM and SIRTA data has
good Rayleigh signal. Should exploit it ! Good Raman lidar data can serve as semi-
independent test of the strengths and weakness of different approaches.
Will first concentrate on Visible extinction retrieval.
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Elastic vs Inelastic scattering
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Cnet October Delft
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No Rayleigh, No RamanThe lidar extinction must first be extracted from the
lidar signal (or, equivalently, the observed lidar backscatter must be corrected for attenuation).
Observed signalCalibrationConstant
Backscatter
Extinction
Ze used to link backscatter and extinction and facilitate extinction correction/determination process.
The retrieved extinction (corrected backscatter) can then be used with the Ze profile to estimate an effective particle size.
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No Rayleigh No RamanMust use Klett (Fernald + Rayleigh)
Must estimate extinction at zm(cloud top)
Very difficult to do directly if one only has lidar info
If have Radar then use smoothness constraint on derived lidar/radar particle size, or extinction, or No*.
But solutions converge if optical depth is above 1 or so !!
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If we have Useful Rayleigh above the cloud.
Then (effectively) can find S and Clid so thatThe scattering ratio R is 1.0 below and above cloud
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If We have good Raman data then…
Direct but noisy
Less noisy butindirect
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Implementation
Cost = Eo + W1*E1 +W2* E2 +W3*E3 + W4*E4
Eo S-S’E1 Force R=1 where no cloud.E2 Minimize derivative of R’effE3Minimize derivative of extE4Minimize derivative of No*
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A Test Case Using GSFC Raman lidar data and ARM MMCR.
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Comparison
Using Rayleigh returnabove cloud
Using smooth Reff (/Ze) constraint
Signature of MS
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Raman RatioRaman Direct
Method 1:Use RayleighMethod 2: Smooth /Ze
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Raman Direct
Method 1:Use RayleighMethod 2: Smooth /Ze
Raman Ratio
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Raman Ratio-vs-Direct
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Combine Methods 1+2(4) !Should work well in thickerClouds also.
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Combine Methods 1+4 (or 2) !Should work well in thickerClouds also.
4
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Ext –vs- Ze
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Conclusions•Multiple scattering effects clearly seen. Appear well accounted for using Eloranta’s approach.
•Should use Rayleigh info if available !
•Aim to create blended approach for non-Raman lidars to smoothly handle range of cases for non-Raman (i.e MPL) where Rayleigh signal from above cloud may or may not be available (almost there).
• Inferring optical depth using Ze alone very tricky on a case-by-case basis.
•Needs robust cloud masking (cld/nocloud/no info)
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Cnet October Delft
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Cnet October Delft
Combine Methods 1+4 (or 2) !Should work well in thickerClouds also.
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Raman Ratio-vs-Direct
Raman Ratio Raman Direct
Raman Ratio Raman Direct
Method 1: Ray above
Method 2: Smooth /Ze
(Raman direct)