WAARSCHUWINGEN GEVAARLIJK WEER

1

Comparing various Lidar/Radar inversion
strategies using Raman Lidar data
D.Donovan, G-J Zadelhof (KNMI) Z. Wang
(NASA/GSFC) D. Whiteman (NASA/GSFC)
2
Introduction

• Background/Rational
• Raman-vs-Elastic backscatter lidars
• Results
• Summary

3
Active (lidar/radar) cloud remote sensing
Radar
Lidar
l 3-100mm
l 350-1100nm
Difference in returns is a function of particle
size !!
4
Rational

• KNMI lidar/radar routine developed for simple
  elastic lR backscatter lidar. No Rayleigh return
• MPL lidar data from ARM 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.

5
Elastic vs Inelastic scattering
6
(No Transcript)
7
No Rayleigh, No Raman

• The lidar extinction must first be extracted from
  the lidar signal (or, equivalently, the observed
  lidar backscatter must be corrected for
  attenuation).

Observed signal
Backscatter
Calibration Constant
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.

8
No Rayleigh No Raman
Must use Klett

• Must estimate extinction at zm(cloud top)
• Very difficult to do directly if one only has
  lidar info
• I 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 !!

9
If we have Useful Rayleigh above the cloud.
Then (effectively) can find S and Clid so
that The scattering ratio R is 1.0 below and
above cloud
10
If We have good Raman data then
Direct but noisy
Less noisy but indirect
11
A Test Case Using GSFC Raman lidar data and ARM
MMCR.
12
Comparison
Signature of MS
Using Rayleigh return above cloud
Using smooth Reff (?/Ze) constraint
13
Raman Ratio
Raman Direct
Method 1Use Rayleigh
Method 2 Smooth ?/Ze
14
Raman Direct
Method 1Use Rayleigh
Method 2 Smooth ?/Ze
15
Method 1 Ray above
Raman Ratio
Raman Direct
Raman Ratio-vs-Direct
Method 2 Smooth ?/Ze
Raman Ratio
Raman Direct
(Raman direct)
16
Conclusions

• Multiple scattering effects clearly seen. Appear
  well accounted for using Elorantas approach.
• Should use Rayleigh info if available.
• Smooth Reff (?/Ze) approach may overestimate
  extinction by factor 1.5 if Tau lt 0.5.
• Will investigate effect of smooth No.
• 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.