CAVIAR Experimenters Meeting 2009 Liam Tallis

© University of Reading 2008 www.reading.ac.ukApril 19, 2023

CAVIAR Experimenters Meeting 2009

Liam Tallis

INTRODUCTION

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Lab View

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Sunsets

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Introduction

• Introduction

• Assessment of the consistency of water vapour lines intensities in recent HITRAN databases

• Towards an absolute calibration

• Water Profile for Jungfraujoch

• Future work

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ASSESSMENT OF THE CONSISTENCY OF WATER VAPOUR LINES INTENSITIES IN RECENT HITRAN DATABASES 6

Consistency Assessment

• Analysis of the consistency of water vapour lines in recent HITRAN databases

• Similar way to Casanova et. al. (2006)

• Optical depth spectrum given by

Where Fm is the measured signal by the FTIR, Fs is the extraterestrial irradiance given

by Kurucz (1995), τm is the optical depth, θ is the solar zenith angle and k(v) is an

unknown calibration factor.

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• Rearrangement ignoring the calibration factor (and a few other approximations)

• We know have a “pseudo” optical depth spectrum

• This spectrum will allow us to analyse the consistency between observation and model

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• Optical depth is calculated for water vapour (τw)

and for five other principle absorbers in the region: CH4, CO2, O2, N2O and O3 (τg) using RFM

(v4.28)

• Linear fit of the “pseudo” optical depth to that calculated by RFM

• Fit pseudo to the form of a x τw + b x τg + c

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a x τw + b x τg + c

• b is tightly bound to be a value between 0.95 to 1.05– An assumption made is other gases well know– Allowed to vary slightly for any minor error in the column

amounts

• c is allowed to vary more freely– c is a offset parameter that varies slowly with wavelength

• a is allowed to vary between 0 and 3– a is the important parameter– tells us the factor line intensities must be multiplied by

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• Camborne Field Campaign

• InSb / CaF2

• Typically for 0.03cm-1 resolution spectra

• Over various days, radiosondes, water columns

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HITRAN2004

HITRAN2008

H08 / H04

Average a 1.0332 1.0375 1.0055

Average a 3000 cm-1 – 8000 cm-1 0.9823 0.9783 0.9961

Average a 8000 cm-1 – 9500 cm-1 1.1614 1.1579 0.9971

Average a 10000 cm-1 - 11500 cm-1 0.9560 0.9762 1.0233


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HITRAN2004

HITRAN2008

H08 / H04

Average a 1.0332 1.0375 1.0055

Average a 3000 cm-1 – 8000 cm-1 0.9823 0.9783 0.9961

Average a 8000 cm-1 – 9500 cm-1 1.1614 1.1579 0.9971

Average a 10000 cm-1 - 11500 cm-1 0.9560 0.9762 1.0233

Ratio of 3000 cm-1 - 8000 cm-1 to 8000 cm-1 – 9500 cm-1

For HITRAN04 = 0.846, St Dev= 0.011For HITRAN08 = 0.845, St Dev= 0.010



• MCT / KBr

• Problems!

• Fit appears to be good...

• But scaling factor required for water vapour lines feels wrong

• Typical “a” value ~ 0.7

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• MCT / KBr

• Typically for 0.03cm-1 resolution spectra

• Over various days, radiosondes, water columns

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HITRAN2004

HITRAN2008

H08 / H04

Average a 700 cm-1 – 1400 cm-1 0.75 0.75 0.99

Average a 800 cm-1 – 1000 cm-1 0.81 0.78 0.96

Average a 1100 cm-1 - 1250 cm-1 0.76 0.74 0.97


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TOWARDS AN ABSOLUTE CALIBRATION

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Towards an Absolute Calibration

• Calibrations before each field campaign at NPL

• NPL produce a calibration function which when used with spectral data gives an irradiance [W/m2/FT o/p unit]

Calibration x Spectral Data = Calibrated Spectra

• Extraterrestrial irradiance given by Kurucz’s (1995) database

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• We know the signal measured by the FT is given by

• And thus by rearranging, we can work out the optical depth

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• Microtops II Sunphotometer

• 13/08/2008

• AOT380 = 0.465, AOT440 = 0.486, AOT675 = 0.577, AOT936 = 0.705, AOT1020 = 0.608

• Campaign Average

• AOT380 = 0.22, AOT440 = 0.17, AOT675 = 0.12, AOT936 = 0.09, AOT1020 = 0.08

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WATER PROFILE FOR JUNGFRAUJOCH

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Water Profile for Jungfraujoch

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• Radiosonde (Payerne)

• Dropsonde (FAAM)

• FAAM Aircraft

• GPS IWV

• ECMWF Forecast Fields

• STARTWAVE Database, University of Bern– GPS Water Vapour– Column Water from Payerne Radiosonde


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371st August 2009

FUTURE WORK

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Future Work• Analysis of the consistency of water vapour lines in

recent HITRAN databases– Any improvements to MCT fit possible?– Repeat this style analysis for Jungfraujoch– Try with new ACE-FTS extraterrestrial line list (Hase et. al, JQSRT

2009)

• Absolute Calibration– Account for difference between calibrated spectra and

extraterrestrial irradiance (in atmospheric windows)– Use Reading’s RFM + DISORT Code

• Water Profile for Jungfraujoch– Continued work in this area

• Questions?

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CAVIAR Experimenters Meeting 2009 Liam Tallis

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