© University of Reading 2008 www.reading.ac.uk

Department of Meteorology

Deriving the Extraterrestria

l Solar Spectrum

Kaah Menang, Liam Tallis , Igor Ptashnik and Keith Shine.

CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Outline• Available TOA Solar Spectra• Motivation and Introduction• Method• Preliminary Results(Jungfraujoch/Camborne)• Filtering of Spectrum (from Camborne

Observations)• Discussion• Future Work

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Available TOA Solar Spectra• “Kurucz” spectrum derived using empirical

relationships covers from 50-50000 cm-

1(kurucz.harvard.edu).• ACE-FTS (IR) solar spectrum obtained from solar

occultation measurements covers from 700-4430 cm-1. Resolution = 0.02 cm-1. Not an absolute spectrum due to absence of calibration of ACE-FTS (Hase et al, 2010).

• Composite solar spectrum from ATLAS/EURECA missions and other sources. From 0.5-2400 nm( ~4200-100000000 cm-1) . 1nm resolution . Poor representation of detailed solar spectrum (Thuillier et al, 2004)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Motivation and Introduction• Crucial to know the TOA solar spectrum.• Test how accurate the widely used “Kurucz”

spectrum is in representing the true solar spectrum.

• Langley method based on Bouguer-Lambert-Beer’s Law:

• Natural logs:4

)exp(0 mFF

mFF 0lnln

CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Method

• Plot against m (Langley plot) for different wavenumbers.

• Linear regression performed on the plot and the

line extrapolated to the point where m = 0.

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Fln

mFF 0lnln

CAVIAR Meeting, NPL Teddington (London) (29 September2010)

MethodAdapted from Petty, G . ‘ A First Course in Atmospheric Radiation’ (Second Edition(2006), page 186)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Method

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• is the exponential of the value of at

m = 0.• NPL observations using a FTS during the CAVIAR

field campaigns in Camborne and Jungfraujoch used. So far preliminary calibration of FTS by NPL used.

• MATLAB code written to perform Langley plots and linear regression automatically.

• 22 August 2008 and 4 August 2009 observations used.

0F Fln

CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Preliminary Results

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Preliminary Results

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Preliminary Results(Jungfra)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Preliminary Results(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Filtering(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Filtering(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Filtering(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Filtering(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Filtering(Camborne)

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Discussion/Future Work• Good fit in both micro-windows and line centres

(very low RMSE values).• Able to detect lines not found in “Kurucz”

spectrum but found in ACE-FTS spectrum.• Line positions the same for both Jung/Camborne

spectrum• 30 % difference between our spectrum from

Jungfraujoch and Kurucz’s spectrum but 5 % difference between our spectrum from Camborne and Kurucz’s spectrum.

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CAVIAR Meeting, NPL Teddington (London) (29 September2010)

Discussion/Future Work• Do analysis before /after local noon

independently, analysis for other days.• Filtering of spectrum using other techniques .• Analysis of aerosol optical depths obtained

using the sun photometer.

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