High resolution solar reference spectrum Robert Voors KNMI.
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Transcript of High resolution solar reference spectrum Robert Voors KNMI.
![Page 1: High resolution solar reference spectrum Robert Voors KNMI.](https://reader036.fdocument.pub/reader036/viewer/2022081514/5a4d1b317f8b9ab05999b59d/html5/thumbnails/1.jpg)
High resolution solar reference
spectrumRobert Voors
KNMI
![Page 2: High resolution solar reference spectrum Robert Voors KNMI.](https://reader036.fdocument.pub/reader036/viewer/2022081514/5a4d1b317f8b9ab05999b59d/html5/thumbnails/2.jpg)
Introduction Solar Reference spectra used for
calibration Wavelength calibration Radiometric calibration
Current spectra do not meet requirements Spectral resolution and sampling Radiometric accuracy
![Page 3: High resolution solar reference spectrum Robert Voors KNMI.](https://reader036.fdocument.pub/reader036/viewer/2022081514/5a4d1b317f8b9ab05999b59d/html5/thumbnails/3.jpg)
Available solar reference spectraChance and Spurr:
composite high resolution Kurucz:
model spectra Thuillier et al:
composite medium resolutionSUSIM on ATLAS and UARS:
low resolution <410nm; long time periodASTM solar standard spectrum
Composite medium resolutionGOME, SCIAMACHY…Many more…
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What’s the problem?
Bladibla
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Combine best of both worlds High resolution spectrum:
assume relative line strengths are OK Low resolution spectrum:
assume absolute radiances are OK.
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Recipe for a new reference spectrum1. Convolve a high resolution spectrum with
poor radiometric calibration with the best slit function that is available for the lower-resolution solar reference spectrum
2. Interpolate the thus obtained high sampling, low-resolution spectrum on the wavelength grid of the low-resolution reference spectrum
3. Divide that spectrum by the low-res spectrum, to obtain the fraction by which to multiply the original high-resolution spectrum, used in 1
4. Interpolate the fraction from 3 to the high resolution wavelength grid
loreshireshisamplores SFF
)(Regrid hisamplores
losamplores FF
measlores
losamplores
losamp FFQ
)(Regrid losamphisamp QQ
hires
hisampREFhires FQF
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Recipe for a new reference spectrum The original high resolution spectrum How to find the best low(er)-resolution
reference spectrum How to determine the instrument transfer
function (slit function) of the low-resolution instrument.
Wavelength calibration of the low-resolution spectra.
![Page 8: High resolution solar reference spectrum Robert Voors KNMI.](https://reader036.fdocument.pub/reader036/viewer/2022081514/5a4d1b317f8b9ab05999b59d/html5/thumbnails/8.jpg)
The original high resolution spectraSpectrum Wavelength
Range [nm]
Spectral
Resolution [nm]
Spectral
Sampling [nm]
Reference
Hall &
Anderson
200-310 ~0.025 0.01 1
Kitt Peak 296-1300 <0.005 0.0003-0.001 2
(1) Balloon spectrum, corrected for atmospheric effects.(2) Ground-based measurements (Kurucz 1984), corrected for atm. effects
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The original low resolution spectrum
Spectrum Wavelength
Range [nm]
Spectral
Resolution [nm]
Spectral
Sampling [nm]
Reference
SUSIM < 410 ~0.15 0.05 1
Heidelberg
balloon
400 - 652 ~1.5 0.25 2
(1) Average of ~1 solar cycle of SUSIM data(2) LPMA balloon measurement from SCIAMACHY validation
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The instrument transfer function
SUSIM: • scanning• triangular
LPMA: • non-scanning• flat/gaussian
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Wavelength scale of low resolution spectra
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Final result
CaII H&K
Comparison at 1 nm resolution
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Solar variability
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Discussion Solar variability not a serious issue, except near 270 nm and
at strong Fraunhofer lines CaII H&K lines pose a problem New spectrum compares well with other solar spectra, e.g.
from SCIAMACHY and Thuillier. Differences mostly < 4 percent Differences possibly due to
Solar reference spectrum Absolute radiometric scale of Thuillier, OMI, SCIAMACHY etc. Assumed low-res slit function Wavelength calibration