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CAVIAR Experimenters Meeting 2009 Liam Tallis. Introduction. Lab View. Sunsets. 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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CAVIAR Experimenters Meeting 2009 Liam Tallis
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
Assessment of the consistency of water vapour lines intensities in recent HITRAN databases
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.
Consistency Assessment • 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
Consistency Assessment • 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
Consistency Assessment 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
Consistency Assessment • Camborne Field Campaign • InSb / CaF2 • Typically for 0.03cm-1 resolution spectra • Over various days, radiosondes, water columns
Consistency Assessment Ratio of 3000 cm-1 - 8000 cm-1 to 8000 cm-1 – 9500 cm-1 For HITRAN04 = 0.846, St Dev= 0.011 For HITRAN08 = 0.845, St Dev= 0.010
Consistency Assessment • Camborne Field Campaign • MCT / KBr • Problems! • Fit appears to be good... • But scaling factor required for water vapour lines feels wrong • Typical “a” value ~ 0.7
Consistency Assessment • Camborne Field Campaign • MCT / KBr • Typically for 0.03cm-1 resolution spectra • Over various days, radiosondes, water columns
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
Towards an Absolute Calibration • We know the signal measured by the FT is given by • And thus by rearranging, we can work out the optical depth
Towards an Absolute Calibration • 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
Water Profile for Jungfraujoch • Radiosonde (Payerne) • Dropsonde (FAAM) • FAAM Aircraft • GPS IWV • ECMWF Forecast Fields • STARTWAVE Database, University of Bern • GPS Water Vapour • Column Water from Payerne Radiosonde
Water Profile for Jungfraujoch 1st August 2009
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?
