# Presentation: 552720

## Depolarization: Multiple Scattering Effect and Its Impact on Water/Ice Determination for PICASSO Lidar 

- Yong X. Hu1, David Winker1, Ping Yang2, Lamont Poole1
*NASA Langley Research Center*
*UMBC*

## Aqua Train and PICASSO

- 		**	**
- _Launch_   _Satellite_           	_Primary Mission_
-   2001    	Aqua                    	water/energy cycle
-   2004    	PICASSO-CENA 	aerosols & clouds
-   2004   	CloudSat              	clouds
-   2003    	Aura                     	atmos. chemistry
-   2004    	PARASOL            	aerosols & clouds

## One of the objectives: learn more details about clouds

## PICASSO Instruments

- Lidar (3 channel):
-     532 nm, 1064 nm, 532 nm
-     0.13 mrad receiver FOV (70 m)
- Infrared Imager (3 channel):
-      8.5m, 10.5m, 12m;
-      pixel size: 1 km
- Visible Camera:
-      pixel size: 125 m

## Cloud type from WFC, IIR and Lidar

- Cloud type will be determined with high resolution visible, mid-IR images, and Lidar.

## Ice cloud microphysics database

*Sassen, 2000*

## The focus of the talk today

- Is it possible to use PICASSO Lidar to tell the difference between water clouds, ice clouds and mixed-phased clouds?

## Water Cloud Frequency from MODIS While 253K < Tc < 268K

*Baum, 2001*

## Water? Ice? – Different discriminating methods

- Passive Instruments:
-    1. T(8.5m) - T(11m)   (ice cloud is warmer at 8.5m)
-     2. R(1.6m)/R(Visible)  (ice cloud absorbs more at 1.6m)
-     3. Polarization characteristics (water cloud rainbow peak)
- Active Instruments (Lidar):
-      zero (water), or not (ice)

## Depolarization: 
When Lidar signal comes from single scattering
    =0 (spherical particles) 
     >0 (non-spherical particles)
When Lidar signal comes from multiple scattering,  

- When Lidar signal comes from single scattering
-     =0 (spherical particles)
-      >0 (non-spherical particles)
- When Lidar signal comes from multiple scattering, 

******: Water/Ice Information**

## : Ground Based Lidar Measurement

- For most ground based measurements, Lidar backscattering signals come from single scattering. It is relatively easy to discriminate water and ice particles
-  *Sassen, 2000*

## PICASSO water/ice determination

- Advantage over passive instruments:
-    better understanding of vertical profile
- Issues need to be addressed:
-     1. what is the impact of multiple scattering?
-     2. water droplet and uniformly oriented plate

## Depolarization from Multiple Scattering: Monte Carlo Simulation

## Monte Carlo Model

## Analytical method is much faster for Lidar Monte Carlo simulations

## Analytic method converges to the correct solution

## Polarization treatment

## and 

## Phase matrix calculations

-  Water clouds:
-     Mie scattering
-     size distributions with 10% dispersion
-  Ice clouds:
-     various shapes and sizes
-     Improved geometric ray tracing
-     FTDT

## : water clouds, various extinction coefficients 

## : ice clouds, various extinction coefficients 

## : ice clouds, different shapes

## : plates, different aspect ratios

## : ice over water, water over ice

## Summary

- depolarization ratios increases toward cloud base gradually for water cloud, while d is large at cloud top and does not change very much toward cloud base
-  for clouds with moderate extinction coefficients, multiple scattering will not cause big problem toward water / ice determination using PICASSO Lidar observations