1

Implications for Molecular Spectroscopy Inferred from IASI Satellite Spectral Measurements

Tony Clough

Clough Associates

Mark Shephard and Vivienne Payne

AER, Inc.

2

Other Collaborators

Bill Smith Stanislav (Stas) Kireev

Water Vapor Line Parameters– Laurent Coudert

– Jean-Marie Flaud

Carbon Dioxide Line Parameters– Jean-Michel Hartmann

3

IASI Scan Rate  8 secs  Scan Type  Step and dwell  Pixel IFOV  0.8225°  IFOV size at Nadir  12 km  Sampling at Nadir  18 km  Earth View Pixels / Scan  2 rows of 60 pixels

each  Swath  ± 48.98°  Swath  ± 1066 km Spectral Range  645 to 2760 cm-1 Resolution (hw-1/e)  0.25 cm-1 Lifetime  5 years Power  210 W Size  1.2 m x 1.1 m x 1.3 m Mass  236 kg Data rate  1.5 Mbps Radiometric Calibration  < 0.1 K

Introduction

• The IASI programme is led by

• Centre National d'Études Spatiales (CNES) in association with EUMETSAT.

Alcatel Alenia Space is the instrument Prime Contractor.

4

Spectral Residuals are Key!

Consistency within a band system 2 band to investigate consistency for H2O

Consistency between bands– IASI 2 and 3 bands to investigate consistency for CO2

Consistency between species– TES: temperature from O3 and H2O consistent with CO2 ; N2O

Consistency between instruments- IASI - TES - NAST-I

- AIRS - MIPAS - AERI

- ACE - SHIS

What is ‘Truth’?

5

SO

ND

E

IASI/LBLRTM Validation

IAS

IR

ETV

6

Temperature

1000

100

10

-3 -2 -1 0 1 2 3P

ress

ure

(m

b)

Difference from Sonde (K)

Difference betweenRetrieval and Sonde

1000

100

10

200 210 220 230 240 250 260 270 280 290

Pre

ssu

re

(m

b)

Temperature (K)

Sonde

Retrieved

Profile

7

Water Vapor v2 Region

Larger residuals remain: IASI Noise: ~0.15K Atmospheric state: retrieved Likely Spectroscopy

Coudert water vapor intensities?

8

Water Vapor v2 Region : Impact of Coudert Intensities

1000

100

50

-20 -10 0 10 20 30 40 50

Pre

ssur

e (m

b)

% Difference from Sonde

HITRAN06

Coudert

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-20 -10 0 10 20 30 40 50

Pre

ssur

e (

mb)

% Difference from Sonde

HITRAN06

Coudert

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-20 -10 0 10 20 30 40 50

Pre

ssur

e (

mb)

% Difference from Sonde

HITRAN06

Coudert

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Detail of Band Center

256

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-10123456

1560 1570 1580 1590 1600 1610 1620 1630 1640

Bri

gh

tne

ss T

em

pe

ratu

re

(K)

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Bri

gh

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(K)

BT

Res

idua

ls

(K)

IASI

LBLRTM Tsfc= 284.323

Residuals: O-C

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Line Parameters:– Niro, F., K. Jucks, J.-M. Hartmann, Spectra calculations in central and wing regions of CO2 IR bands.

IV : Software and database for the computation of atmospheric spectra: J Quant Spectrosc Radiat Transfer., 95, 469-481.

– P, Q, & R line coupling for bands of importance

– Niro et al. code modified to generate first order line coupling coefficients, yi.

– Works in regular line by line mode with LBLRTM

– Temperatures: 4

Line Shape:– Impact Approximation

– Duration of collision effects under study

Continuum:– Factor– Sampled 2 cm-1

– New definition required

– Temperature dependence ??

CO2 Line Coupling : Effect on Spectra

LBLRTM Chi Factor for CarbonDioxide

Line Coupling - Duration of Collision

Clough/Burch/Benedict based on 3 band

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20 25

Chi

Fun

ctio

n

Wavenumber from Line Center (cm-1)

Impact - This Work

Clough et al, 1978

Cousin (a) N2 296K

Cousin (c) N2 238K

Cousin (a) O2 296

Cousin (c) O2 238

Chi Factor

11

Line Coupling

ik ( ) 1

iS2 i

i

2

Lorentz (Impact) 

i

iy i

Line coupling coefficient: yi

k () 1

iS i

2 i i

2i

1

iS  

iy

i

2 i i

2i

far fromlinecenter : i

i e.g. continuum

1

iS i

2 i i 1

iS  

iy

i 2 i i

let  i

  o i               far fromband center  with    o

i     

   

1

  1

2 o  

iS i      i    1

  1

2 o  

iS iy   i     i

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-0.00002

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0.00016

0.00018

600 620 640 660 680 700 720 740Wavenumber (cm-1)

v11.1

Q-Branch

-0.00002

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0.00016

0.00018

600 620 640 660 680 700 720 740Wavenumber (cm-1)

v11.1

v11.2

-0.00002

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0.00016

0.00018

600 620 640 660 680 700 720 740Wavenumber (cm-1)

v11.2

quad impact

quad cpl

New Definition for Continuum Function

-4

-3

-2

-1

0

1

2

3

4

630 640 650 660 670 680 690 700 710Wavenumber (cm-1)

v11.1

v11.2

0

0.002

0.004

0.006

0.008

0.01

0.012

630 640 650 660 670 680 690 700 710Wavenumber (cm-1)

v11.1

v11.2

Line Couple Component

Single Line

-4

-3

-2

-1

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3

4

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v11.1

v11.2

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0.012

630 640 650 660 670 680 690 700 710Wavenumber (cm-1)

v11.1

v11.2

Impact Component Quadratic

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CO2 v3

Temperature: CO2 Spectral Regions

CO2 v2

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CO2 ContinuumSymmetrized Power Spectral Density Function

1E-6

1E-5

1E-4

1E-3

600 620 640 660 680 700 720 740Wavenumber (cm-1)

quad

quad impact

abs(Cpl) (quad)

mt_ckd_2.0

1E-6

1E-5

1E-4

1E-3

2250 2270 2290 2310 2330 2350 2370 2390 2410 2430 2450Wavenumber (cm-1)

quad

quad impact

abs(Cpl) (quad)

mt_ckd_2.0

2

1E-6

1E-5

1E-4

1E-3

600 620 640 660 680 700 720 740Wavenumber (cm-1)

quad

quad impact

abs(Cpl) (quad)

mt_ckd_2.0

1E-6

1E-5

1E-4

1E-3

2250 2270 2290 2310 2330 2350 2370 2390 2410 2430 2450Wavenumber (cm-1)

quad

quad impact

abs(Cpl) (quad)

mt_ckd_2.03

0E+0

1E-8

2E-8

3E-8

4E-8

5E-8

6E-8

7E-8

-1.0E-8

-5.0E-9

0.0E+0

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1.5E-8

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2.5E-8

2350 2360 2370 2380 2390 2400 2410 2420 2430 2440 2450

Rad

ianc

e (W

/m2/

sr/c

m-1

)

Ra

dia

nce

O -

C

(W/m

2/s

r/cm

-1)

Wavenumber (cm-1)

IASI

LBLRTM Tsfc= 284.323

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CO2 ContinuumSymmetrized Power Spectral Density Function

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Impact of CO2 Line Coupling in the Infrared

CO2 v2

CO2 v3

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Summary • Water Vapor:

- Line Intensity IssueInternal consistency is not necessarily conclusive

- Residuals are too largeWidths and Shifts ?

• Carbon Dioxide:- Line Coupling is the key!

- CO2 Continuum has been reduced by 25% for best fit at bandhead

- 2 and 3 approaching consistencyImproved Tashkun 3 line parameters

- Resolution of remaining residualsSmall factor for duration of collision effects

• Retrievals for other species are excellent

• Updated Code and Line Parameters are available- Separate Line Coupling file (Hartmann) available: aer_v2.1

• Spectral Residuals must become the validation criterion

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METHANE

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re

(K)

BT

Re

sid

ua

ls

(K)

Wavenumber (cm-1)

IASI

LBLRTM Tsfc= 284.323

Residuals: O-C

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IASI

C’est Incroyable !

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1000

100

50

-20 -10 0 10 20 30 40 50

% Difference from Sonde

HITRAN06

Coudert

Effect of Line Parameters onRetrieved Water Vapor Profiles

Water Vapor

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1 10 100 1000 10000 100000

Pre

ssur

e

(mb)

VMR (ppm)

Sonde

Retrieval_2

Profile

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SO

ND

E

IASI/LBLRTM Validation

RETV

IAS

IR

ETV

22QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Status of Two Key Elements of the Forward Model in the Longwave:

Carbon Dioxide Spectroscopy and the Water Vapor Continuum

Tony Clough

Atmospheric & Environmental Research, Inc.

EGU, Vienna

16 April 2007

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Carbon Dioxide Spectroscopy

Acknowledgments

• University of WisconsinHank Revercomb, Bob Knuteson and Dave Tobin

• TES TeamLinda Brown, Aaron Goldman, Curtis Rinsland, Helen Worden, etc., etc.

• CreteillJean Michel Hartmann’s Group

Mark Shephard and Vivian Payne

Observations

• Tropospheric Emission Spectrometer (TES)

• Scanning High Resolution Interferometric Sounder (SHIS)

• Atmospheric InfraRed Spectrometer (AIRS)

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Forward ModelSpectral Radiance

MeasuredSpectral Radiance

Radiating Atmosphere/Surface

Specification of Atmospheric State

?

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TES - SHIS Radiance Comparison

• TES Convolved to SHIS ILS

• {TES - LBLRTM(TES Geometry)} - {SHIS - LBLRTM(SHIS

Geometry)}

TES CO2 Filter: 2B1

TES Ozone Filter: 1B2

TES Water Filter: 2A1

Error in O3 above SHIS

Error in CO2 above SHIS

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(AIR

Sob

s-A

IRS

calc

)-

(S

HIS

obs-

SH

ISca

lc)

(K) AIRS / SHIS Brightness Temperature Comparison

Excluding channels strongly affected by atmosphere above ER2

Histograms

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SHIS Analysis from AURA Validation ExperimentPersistent Spectral Residuals

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LBLRTM Approach for Carbon Dioxide (up to this point)

ik ( ) 1

iS2 i

i

2

Lorentz Impact

  i

i: line coupling and

duration of collision effects

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Line Coupling Parameters for the 5 < 2 Band

-3.25

-3.00

-2.75

-2.50

-2.25

-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

0.25

-0.07

-0.05

-0.03

-0.01

0.01

0.03

0.05

0.07

715 717 719 721 723 725

630 650 670 690 710 730 750 770 790Q

Bra

nch

Ys

P, R

Bra

nch

Ys

Wavenumber (cm-1)

Wavenumber (cm-1)

Q Branch Hartmann et al.

Q Branch Hoke et al.

P Branch Hartmann et al.

R Branch Hartmann et al.

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SHIS Analysis from AURA Validation ExperimentGulf of Mexico - no sonde

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AIRS Analysis ARM Tropical Western Pacific site - sonde

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Summary 1

• Forward Model for Temperature Retrievals significantly improved- P-R line coupling is a key element

• Carbon Dioxide:- factor and continuum strongly influenced by line coupling

- need to introduce small factor for duration of collision effects

- CO2 Continuum has been reduced by 25% for best fit at bandhead

• 2 and 3 are apparently not yet fully consistent

• Line Coupling for N2O

• Updated Code and Line Parameters to be made public- separate Line Coupling file (Hartmann) available: TAPE2

• Spectral Residuals will likely become the validation criterion

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MT_CKD Water Vapor Continuum Model

• Definition: Continuum is that absorption with slow spectral dependence which,

when added to the line by line absorption, provides agreement with measurement.

• Scaling: Dependence on pressure, temperature and mixing ratio must be correct

• The model is based on contributions from two sources:

1. Allowed line contribution

- Line wing formalism constrained by the known physics with relevant

parameters (~2) determined from laboratory and atmospheric Measurements

- Same line shape is used for every line from the Microwave to 20,000 cm-1

2. Collision-Induced contribution

- Provides the extra absorption previously provided by the ‘super Lorentzian’ chi factor

- Based on dipole allowed transitions with widths ~ 50 cm-1

- Same line shape is used for every line from the Microwave to UV

• The model includes both self and foreign continuum

• Spectral region: 0 - 20,000 cm-1

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AIRS Analysis ARM Tropical Western Pacific site - sonde

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Summary 2

• Issues with water vapor continuum have become remarkably muted

• Collision induced component addresses measurement issues- No direct validation of mechanism is apparent

• Self and Foreign each use a single separate line shape for all lines to construct the respective continua over full frequency domain

• Self Continuum (line wing component) dominant between bands

• Foreign Continuum (collision induced) dominant within bands

• Well Validated in 0-10 cm-1 (microwave); 400-500 cm-1; 800 -1300 cm-1; and 2500-2700 cm-1 (SST)

• Validations needed 10-400 cm-1 and Shortwave

• Temperature Dependence! Laboratory Measurements (Lafferty)

• MT_CKD Water Vapor Continuum is publicly available

- http://rtweb.aer.com