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

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Presentation on theme: "QA/QC of Solar spectral UV-measurements: Checking for wavelength shifts and spectral shape deviations with focus on error flagging Harry Slaper, PN den."— Presentation transcript:

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) 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 nm)=>comparing spectra  High accuracy wavelength calibration required (wavelength shift of nm => 1% change in Effective UV)

4 Wavelength Shift Analysis

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6 Correction for slit function effects  Measured spectrum: M( )  Iterative ‘Deconvolution’ technique - start spectrum S 0 ( ) (high resol.) - simulate measurement M s0 ( ); - correct start spectrum: S 1 ( ) = (M( ) / M s0 ( )) S 0 ( )  Repeat steps until: S 9 ( )

7 Wavelength shift uncertainties  Reproducability error< 0.01 nm (FWHM <= 1 nm)  Alignment error 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

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19 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)

20 R = mean SD of 1 min readings

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

22 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) 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%)

23 !SHICrivm version ; Harry Slaper LSO/RIVM, ! Quality check shift and structure ! sh1 refers to average shift over wavelength interval: ! sh2 refers to average shift over wavelength interval: ! start_wave indicates effective UV below lowest wavelength where 5 successive readings ! meet criterium for structural checks: ! spike and instability checking above the starting wavelength sza: shift1 flagging : GREEN (nm) shift2 flagging : GREEN (nm) spike and instability flag: GREEN INSTABLE 3.04 % start wavelength flag : YELLOW (nm) efuv below: 0.49 % last wavelength flag : GREEN (nm) efuv above: 1.92 %

24 SHIC status  Version 2.79 released october 2000; 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

25 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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