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The Status of the LBLRTM Forward Model:Implications for Remote Spectral Measurements

Tony CloughClough Radiation Associates

Mark Shephard, Vivienne Payne and Jennifer DelamereAER, Inc.

Bill Smith and Stas KireevHampton University

Advanced High Spectral Resolution Infrared ObservationsEUMETSAT

16 September 2008

More Spectroscopy Than You Ever Hoped to Hear About

Tony CloughClough Radiation Associates

Mark Shephard, Vivienne Payne and Jennifer DelamereAER, Inc.

Bill Smith and Stas KireevHampton University

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Collaborators

• Water Vapor Line Parameters– Laurent Coudert– Jean-Marie Flaud– Linda Brown– Bob Gamache

• Carbon Dioxide Line Parameters– Jean-Michel Hartmann– Niro– Tashkun– Jean-Marie Flaud

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LBLRTM Considerations

• Bugs Bugs Bugs Bugs

- AJ Problem in continuum module: Fixed (Karen Cady-Pereira)

- Different results for a given spectral domain depending on starting frequency

- Last layer AJ problem: Fixed (Tony Clough)

- Problem in Fourth function for extremely small optical depths: Fixed (Mark Shephard)

- NaN NaN NaN

• Releases and Archiving

• LBLRTM Issues

- Changing water in a layer > changes layer boundary altitudes > changes level temperatures

- Simultaneous temperature and water vapor retrievals are effected

- Fix boundary altitudes on input (hydrostatic equation not satisfied)

- AJ: self broadening of water vapor lines is not treated

- Upwelling Radiance Calculations: Currently NO capability to include downwelling radiance at upper boundary

- Not a problem for TOA

- Problem for HIS, e.g. ozone

- Problem for AJ

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• Spectral Residuals are Key!

• Consistency within a band system− ν2 band to investigate consistency for H2O

• Consistency between bands– IASI ν2 and ν3 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’?

?

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Temperature Retrievals

• Carbon Dioxide

- Niro et al. Line Coupling- implications for co2 continuum

- Accuracy of collision rates

- Limitations of impact approximation

- Significant impact on our understanding of absorption far from band center

- Chi factor- duration of collision effects

- Line intensities- MIPAS line strengths

- Tashkun, Teffo, Flaud et al.

- H2O broadening of CO2

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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:– Χ Factor– Sampled 2 cm-1

– New definition required

– Temperature dependence ??

CO2 Line Coupling : Effect on Spectra

Line Coupling - Duration of CollisionClough/Burch/Benedict based on ν3 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

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Line Coupling

ik (ν) =1π

iS2ν− iν( ) + i

2α

Lorentz (Impact)

iα +

iy ν − iν( )⎡

⎣⎤⎦

Line coupling coefficient: yi

k (ν) =1π

iS iα2ν − iν( ) + i

2αi∑ +

1π

iS i

y ν − iν( )⎡

⎣⎤⎦

2ν − iν( ) + i

2αi∑

far fromlinecenter : ν − iν( )>>i

α e.g. continuum

=1π

iS iα2ν − iν( )i

∑ + 1π

iS i

y ν − iν( )⎡

⎣⎤⎦

2ν − iν( )i∑

let iν = oν + iδ far fromband center with ν − oν( )>>iδ

=1π

12ν − oν( )

iS iα

i∑ + 1

π 1

2ν − oν( )

iS iy iδ i

∑

8

-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

600 620 6 0 660 680 00 20 0

v11.1v11.2

600 620 640 660 680 00 20 40

v11.2quad impactquad 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

Line Couple Component

Single Line

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

Impact Component Quadratic

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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_2.0ν2

1E-6

1E-5

1E-4

1E-3

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

ν3

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

5.0E-9

1.0E-8

1.5E-8

2.0E-8

2.5E-8

2350 2360 2370 2380 2390 2400 2410 2420 2430 2440 2450

Rad

ianc

e (W

/m2/

sr/c

m-1

)

Rad

ianc

e O

- C

(W

/m2/

sr/c

m-1

)

Wavenumber (cm-1)

IASI

LBLRTM Tsfc= 284.323

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CO2 ContinuumSymmetrized Power Spectral Density Function

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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/hh) 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.

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IASI JAIVEx 19 April

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IASI/LBLRTM ValidationSO

ND

EIA

SIR

ETV

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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

ssur

e

(mb)

Temperature (K)

SondeRetrieved

Profile

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IASI - LBLRTM_v11.3

-2 K

CO2 ν3 spectral region

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‘Bandhead’ CO2 ν3 spectral region

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• Water Vapor

- Variability: Horizontal / Vertical / Time

- Residuals are consistently greater than IASI noise

- Coudert et al. Line Strengths

- Line Widths

- Continuum

- 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

- Implications from downwelling spectra at the ARM NSA site.

Water Vapor Retrievals

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Water Vapor ν2 Region

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

Coudert water vapor intensities?

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Water Vapor ν2 Region : Impact of Coudert Intensities

1000

100

50

-20-10 0 10 20 30 40 50% Difference from Sonde

Pre

ssur

e (m

b)

HITRAN06Coudert

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IASI 19 AprilWater Vapor

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Detail of Band Center

h2o line coupling

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AERI Downwelling RadiancesARM NSA Site

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SRF file: srftables_031115v3.hdf

AIRS - sarta (v4,tuned)

AIRS - sarta (v4,untuned)

AIRS - lblrtm v11.3

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METHANE

190

200

210

220

230

240

250

260

270

280

290

-1

0

1

2

3

4

5

6

7

8

9

1200 1220 1240 1260 1280 1300 1320 1340 1360 1380 1400

Brig

htne

ss T

empe

ratu

re

(K)

BT

Res

idua

ls

(K)

Wavenumber (cm-1)

IASI

LBLRTM Tsfc= 284.323

Residuals: O-C

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Summary

• Carbon Dioxide:- Line Coupling is the key!- Relaxation Matrix needs adjustment

and/or - Duration of Collision Effects need to be included- CO2 Continuum requires modification- ν2 and ν3 approaching consistency

Tashkun ν3 line parameters to be evaluated− ν2 Q-Branch not yet consistent

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Summary

• Water Vapor:- Line Intensity Issue

Coudert Line Parameters being adoptedInternal consistency is not necessarily conclusive

- Residuals are too large (much larger than IASI noise)- Line Coupling, Widths and Shifts ?

• xx Simultaneous retrieval of Temperature and Water Vapor xx

• Retrievals for other species are generally excellent

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

• Spectral Residuals are a CRITICAL validation criterion

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IASI

C’est Incroyable !

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AIRS/model comparisons

• Mean residuals for 36 “clear-sky” cases– ARM TWP Phase 1 AIRS validation– Layer profiles, AIRS and SARTA radiances supplied by L. Strow and S. Hannon

AIRS - lblrtm v11.3Mean residuals for all “clear-sky” cases

Example case

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Impact of CO2 Line Coupling in the Infrared

CO2 v2

CO2 v3

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CO2 v3

Temperature: CO2 Spectral Regions

CO2 v2

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SRF file: srftables_051118v4.hdf

(d)

(e)

AIRS - sarta (v5,tuned)

AIRS - lblrtm v11.3

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CO2 ν3 line parameters

Profile from IASI JAIVEx case

Up to -11.4 KUp to -8.0 K

Up to 2.4 K

• aer_v2.1: • CO2 line parameters from HITRAN 2K

• HITRAN_MIPAS_3.2:• CO2 line parameters from Tashkun, Teffo, Flaud et al.• Validated by Flaud et al using MIPAS spectra.

• Line coupling coefficients in aer_v2.1 are for HITRAN 2K CO2 line parameters

• Niro et al., 2005 • code supplied by J-M. Hartmann).

• Next: calculate line coupling coefficients for “HITRAN_MIPAS” CO2 line parameters, using same code.

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CO2 ν3 line parameters

Profile from IASI JAIVEx case

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1000

100

50

-20 -10 0 10 20 30 40 50% Difference from Sonde

HITRAN06Coudert

Effect of Line Parameters onRetrieved Water Vapor Profiles

Water Vapor

1000

100

50

1 10 100 1000 10000 100000

Pre

ssur

e

(mb)

VMR (ppm)

SondeRetrieval_2

Profile

36

SON

DE

IASI/LBLRTM Validation

RET

VIA

SIR

ETV

37QuickTime™ 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 CloughAtmospheric & Environmental Research, Inc.

EGU, Vienna16 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 (ν ) =1π

iS2ν− iν( ) + i

2α

Lorentz Impact

χ ν −i

ν( )⎡⎣ ⎤⎦

χi: line coupling andduration 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

630 650 670 690 710 730 750 770 790

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:- χ factor and continuum strongly influenced by line coupling- need to introduce small χ factor for duration of collision effects- CO2 Continuum has been reduced by 25% for best fit at bandhead

• ν2 and ν3 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