Lidar/Infrared radiometer coupling for a better determination of particle size in ice cloud
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Lidar/Infrared radiometer coupling for a better determination of particle size in ice cloud. M.Chiriaco, H.Chepfer, V.Noel, A.Delaval, M.Haeffelin Laboratoire de Météorologie Dynamique, IPSL, France P.Yang, Texas University P.Dubuisson, ELICO, France.

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Lidar/Infrared radiometer coupling for a better determination of particle size in ice cloud

M.Chiriaco, H.Chepfer, V.Noel, A.Delaval, M.Haeffelin

Laboratoire de Météorologie Dynamique, IPSL, France

P.Yang, Texas University

P.Dubuisson, ELICO, France

Science Team CALIPSO – March 2003


A better determination of particle size in ice cloud determination of particle size in ice cloud

Goal : improving split window technique

  • classical split window technique

  • improvement from 532nm lidar : scene identification

  • improvement from lidar depolarisation : shape constrain

  • improvement from 10.6µm lidar : where is the most absorbing layer within the cloud ?

    Synthesis of 5 cases studies

Science Team CALIPSO – March 2003


Classical split window technique
Classical split window technique determination of particle size in ice cloud

Brightness temperature difference between 2 IR channels :

TB(λ1)-TB(λ2)=f(TB(λ1))

Sensitivity to crystal sizes and shapes (3)

sph. liq 6µm

sph. ice 6µm

sph. liq 12µm

sph. ice 12µm

TB(λ1)-TB(λ2)

Optical properties (4)

  • Asymmetry factor

  • Single scattering albedo

  • Extinction cross section

Clear sky

T(λ1)

Opaque cloud

Uncertainty on cloud temperature (2)

Uncertainty on scene identification (1)

Science Team CALIPSO – March 2003


Improvements
Improvements determination of particle size in ice cloud

MEASUREMENTS

Temperature differences between 2 channels

IR radiometer : brightness temperatures

Retrieved several possible values of r, depends on the shape hypothesis

Best solution for (r,Q)

(1)scene identification (2) cloud temperature Lidar + radiosonde

Radiative transfert (P.Dubuisson, ELICO)

Absorption & scattering

Temperature differences between 2 channels

(3) Shape Q deduced from lidar depolarization (V.Noël)

(4) Optical properties for non spherical particles

(P.Yang, Texas Univ.)

SIMULATIONS

improvements

Science Team CALIPSO – March 2003


Applications

Aqua determination of particle size in ice cloud

Cloudsat

Calipso

Parasol

Aura

Applications

TERRA/MODIS

λ1 = 8.65µm

λ2 = 11.15µm

λ3 = 12.05µm

Instrumented site of Palaiseau/France : SIRTA

~ IIR

SIRTA

532 nm lidar

LNA

10.6 µm lidar

LVT

distance : 200m

Science Team CALIPSO – March 2003


Cloud identification improvement from 532nm lidar a

SIRTA determination of particle size in ice cloud

Cloud identification : improvement from 532nm lidar (a)

LNA

220K < Tcloud < 250K

MODIS

TB,SIRTA> Tcloud

semi-transparent cloud

TB,SIRTA = 265K

Science Team CALIPSO – March 2003


T determination of particle size in ice cloud8.7µm-T12µm

T8.7µm-T10.5µm

T10.5µm-T12µm

T10.5µm

T8.7µm

T8.7µm

Cloud identification : improvement from 532nm lidar (b)

  • Clear sky temperature fixed owing to lidar

  • Opaque cloud temperature fixed owing to lidar : cloud top

  • Each curve corresponds to a cloud defined by a (r, Q) value

17µm<r <19µm for 0.15 < shape ratio Q < 0.5

Science Team CALIPSO – March 2003


Shape constrain improvement from lidar depolarization a

SIRTA determination of particle size in ice cloud

Shape constrain : improvement from lidar depolarization (a)

LNA

Tcloud= 220K

TB,SIRTA> Tcloud

semi-transparent cloud

MODIS

TB,SIRTA= 260K

Science Team CALIPSO – March 2003


ΔP determination of particle size in ice cloud

R

L

Shape ratio

Shape constrain : improvement from lidar depolarization (b)

Depolarization ratio

Shape ratio Q

classe I : Q<0.05

classe II : 0.05<Q<0.7

classe III : 0.7<Q<1.05

classe IV : Q>1.05

Noël & al, Applied optics, 2002

Science Team CALIPSO – March 2003


Shape constrain : improvement from lidar depolarization (c) determination of particle size in ice cloud

Cloud identification (backscattering) : 31<r<76µm for 0.15<Q<2

Shape constrain (depolarization) : 31<r<46µm for 0.7<Q<2

Lidar depolarization

Science Team CALIPSO – March 2003


10.6 µm lidar determination of particle size in ice cloud

SIRTA

(Average over 5 minutes)

Absorption profile : improvement from 10.6 µm lidar (a)

Where is the most absorbing layer in the cloud ?

Cloud top temperature?

Cloud base temperature?

Cloud middle temperature?

532 nm lidar

SIRTA

Science Team CALIPSO – March 2003


Absorption profile : improvement from 10.6 µm lidar (b) determination of particle size in ice cloud

We want an absorption profile in infrared to estimate the most absorbing layer within the cloud position of the cold foot in split window

(1)

negligible if r>100µm

negligible for n<103/m3 if r<100µm

k0.5 = k10 (P.Yang)

α = n.Q.(π.r²)

Qsca,0.5 = 2 for r > 1µm

(P.Yang)

We finally have Qabs

Science Team CALIPSO – March 2003


Absorption profile : improvement from 10.6 µm lidar (c) determination of particle size in ice cloud

532nm maximum : 8300m +/- 15m

10.6µm maximum : 7900m +/- 50m

Qabs maximum : 7300m

concentration is not considered : final result of absorption?

This difference could change the temperature of opaque cloud in simulations (position of cold foot), and influence the final result of particle size

Science Team CALIPSO – March 2003


Synthesis of 5 cases studied
Synthesis of 5 cases studied determination of particle size in ice cloud

cloud type (532nm lidar) 3 wavelength constrain shape constrain 10.6µm lidar results

semi transparent

T=220K

TB=260K

2002/03/05 31<r<76µm 31<r<46µm no measurements

0.7<Q<2

2002/04/02 no solutionno solution no measurements

0.05<Q< ∞

2002/10/08 17<r<19µm no improvement

0.15<Q<0.5

2002/10/14 23<r<57µm 23<r<28µm

0.15<Q<0.9 0.7<Q<0.9

2002/11/06 21<r<57µm r~25µm

0.15<Q<0.9 Q=0.9

relatively opaque

T=230K

TB=239K

Max 532nm : 7000m

Max 10.6µm : 7100m

Max Qabs,10 : 7500m

semi transparent

220<T<250K

TB=265K

semi transparent

240<T<250K

TB=245K

Max 532nm : 6000m

Max 10.6µm : 6000m

Max Qabs,10 : 5800m

Max 532nm : 8300

Max 10.6µm : 7900

Max Qabs,10 : 7000

semi transparent+low one

Thigh=240K Tlow=265K

TB=252K

Science Team CALIPSO – March 2003


Perspectives
Perspectives determination of particle size in ice cloud

Further analysis of 10.6µm cases

Validation of the method with in situ measurements :

data from CRYSTAL-Face field experiment (July 2002)

Comparison with method based on more wavelength (Minnis, 1998)

Systematic analysis over SIRTA

CALIPSO (2005) : application of the method to the first spatial observations

Science Team CALIPSO – March 2003


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