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QA/QC of Solar spectral UV-measurements:

QA/QC of Solar spectral UV-measurements:. Checking for wavelength shifts and spectral shape deviations with focus on error flagging. Harry Slaper , PN den Outer, HAJM Reinen. Flagging output. Shift in two wavelength regions: < 325 nm green 0.1 nm yellow 0.2 nm red

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QA/QC of Solar spectral UV-measurements:

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  1. QA/QC of Solar spectral UV-measurements: Checking for wavelength shifts and spectral shape deviations with focus on error flagging Harry Slaper, PN den Outer, HAJM Reinen

  2. Flagging output Shift in two wavelength regions: < 325 nm green 0.1 nm yellow 0.2 nm red > 325 nm green 0.2 nm yellow 0.4 nm red starting wavelength (SZA dependent) < 2-3% error => GREEN spike error flag: shape error > 10% => 2-fold error at single wavelength=> YELLOW at 305 nm corresponds to 2-3 % CIE-error atmospheric variability during the scan: green is subdivided in INSTABLE (shape>3%) HIGHLY INSTABLE (shape>5%)

  3. Shift and deconvolution analysis: why? • Spectral instruments show variation in slit functions (FWHM 0.3 - 2.5 nm)=>comparing spectra • High accuracy wavelength calibration required (wavelength shift of 0.03-0.05nm => 1% change in Effective UV)

  4. Wavelength Shift Analysis

  5. Wavelength Shift Analysis

  6. Correction for slit function effects • Measured spectrum: M() • Iterative ‘Deconvolution’ technique - start spectrum S0() (high resol.) - simulate measurement Ms0(); - correct start spectrum: S1() = (M() / Ms0()) S0() • Repeat steps until: S9()

  7. Wavelength shift uncertainties • Reproducability error < 0.01 nm (FWHM <= 1 nm) • Alignment error 0.01-0.02 nm • Absolute acccuracy < 0.01 nm (depends on Extra Terrestrial)

  8. Solar zenith angle (in)depence of wavelength shifts using SHICrivm (spectra from RIVM UV monitoring)

  9. Shift and deconvolution analysis • Enables high accuracy wavelength calibration • Facilitates direct comparison of spectral readings from different instruments/sites • Enables calculation of Standardized spectral UV-data

  10. Shift and deconvolution software: SHICrivm • wavelength dependent shift • standardized spectrum - shift and slit corrected - shift corrected • effective UV-determination for several Action Spectra • Check on spectral anomalies

  11. Further application of SHICrivm • Determine high resolution quality of ET-spectra (Kitt Peak, Atlas 3) • Slit function; FWHM estimates • Analysis of requirements regarding over/under sampling • Facilitate model/measurement intercomparison

  12. Analysis of spectral shape errors (spikes, cloud variability) • Use ratio of readings at two adjacent wavelengths and compare with expected ratio (SHIC) • identify shortest wavelength with reliable readings (SHIC and ratio method) • identify spikes and cloud variability

  13. Data from Blumthaler SUSPEN 1997

  14. Identification of spikes and spectral shape errors • Spectral shape errors by comparing readings at subsequent wavelengths with ‘expected’ratio • problem how to distinguish between errors and variability • proposal shape error >0.03 instable conditions; >0.05 highly instable; >0.10 YELLOW (spikes flag)

  15. R = 0.812 mean SD of 1 min readings

  16. Correlation of shape errors (10%) and pyranometer variability (mean of SD within minutes; SD between 1 minute readings)

  17. Flagging output Shift in two wavelength regions: < 325 nm green 0.1 nm yellow 0.2 nm red > 325 nm green 0.2 nm yellow 0.4 nm red starting wavelength (SZA dependent) < 2-3% error => GREEN spike error flag: shape error > 10% => 2-fold error at single wavelength=> YELLOW at 305 nm corresponds to 2-3 % CIE-error atmospheric variability during the scan: green is subdivided in INSTABLE (shape>3%) HIGHLY INSTABLE (shape>5%)

  18. !SHICrivm version 3.012 10-06-2001; Harry Slaper LSO/RIVM, harry.slaper@RIVM.NL ! Quality check shift and structure ! sh1 refers to average shift over wavelength interval: 300.00 325.00 ! sh2 refers to average shift over wavelength interval: 325.00 390.00 ! start_wave indicates effective UV below lowest wavelength where 5 successive readings ! meet criterium for structural checks: 0.250 ! spike and instability checking above the starting wavelength 1061024 sza: 44.842 shift1 flagging : GREEN 0.016 (nm) shift2 flagging : GREEN 0.030 (nm) spike and instability flag: GREEN INSTABLE 3.04 % start wavelength flag : YELLOW 299.04 (nm) efuv below: 0.49 % last wavelength flag : GREEN 379.50 (nm) efuv above: 1.92 %

  19. SHIC status • Version 2.79 released october 2000; 3.012 now tested; UNIX version tested • flagging included; faster (1-2 sec per spectrum) • spectral shape checks improved • shifts below 300 nm possible • further improvement: output control

  20. Next year activities • New release of SHIC december 2001 • Application of flagging on subsets of data • Use in climatological analysis (calculation of effective UV in standardized way) • improvement of algorithm to identify atmospheric variability during the scans (OE) • implementation at the database (in collaboration with FMI, Ola Engelsen) • uncertainty analysis in relation to FWHM

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