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Post processing of data from array
spectroradiometer
«Workshop-Tutorial»
Luca Egli1 , Julian Gröbner1 and M. Blumthaler2
1Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos Switzerland
2Innsbruck Medical University, Biomedical Physics, Innsbruck, Austria
The European Metrology Research Programme (EMRP) is jointly funded by the EMRP participating countries
within EURAMET and the European Union.
Uvnet Workshop , Davos, 15-16 July 2014
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PMOD Intrument «AVOS»
Avantes AvaSpec ULS2048 /CCD Hamamatsu back illuminated Wavelength: 280 – 390 nm (irregular grid)
Array spectroradiometer
Double monochromator
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Adressing Data Post Processing
1. Data Acquisition
2. Linearity correction
3. Dark Measurements
4. Handling several integration times
5. Stray Light Corrrection
4. Bandwidth and wavelength correction / homogenization
“Matshic”
5. Discussion of experience of users of other array
spectroradiometers
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Data Acquisition
Setting integration time and dark measurement
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Data Acquisition
Setting integration time
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Data Acquisition
Setting integration time
Be careful in
changing Integration
times !!
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Data Acquisition
Setting dark measurement
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Data Acquisition
Monitoring schedule
1000 ms 9000 ms
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After Linearity correction: Dark Measurements
Subtracting dark measurements for each scan and integration time
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Linearity correction
Correcting raw signal (in counts) for linearity
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Normalized Signal
Dividing to integration time [counts/ms]
«Blooming Effect»
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Compariosn of normalized signal
Dividing to integration time [counts/ms]
<1 %
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Noise reduction
Effect of longer integration time
Significant noise reduction
Longer integration time reduce
noise more than averaging
several spectra!
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Merging
Selecting best parts of the normalized signal
Significant noise reduction
Merging both spectra together
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Stray Light Correction
Raw Measurement
Out-range Corrected
In&Out-range Corrected
This Array Spectroradiometer
• Nominal Sensitivity: 280 – 440 nm • Out-range Radiation from 440 nm to ~1100
(Silicon) nm
This instrument only In-Range stray light correction
Double MC
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Modification of array spectroradiometer to suppress out-range radiation
We placed a DUG11X solarblind filter in the beam path to suppress out-range radiation in the sensi-tivity range of the silicon CCD detector (390-1100 nm).
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Modification of array spectroradiometer to suppress out-range radiation
We placed a DUG11X solarblind filter in the beam path to suppress out-range radiation in the sensi-tivity range of the silicon CCD detector (390-1100 nm).
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Stray light correction procedure for array spectroradiometer
Slit Functions obtained from tunable laser setup (PLACOS-PTB) - > creating matrix
1IB meas meas
Y A Y C Y
from Zong et al, 2006
In-range straylight matrix
OoR straylight (Nevas et al. 2012)
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Applying Stray Light Correction
This instrument only In-Range stray light correction between 280 and 390 nm
Linear corrected and normalized signal [counts/ms]
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Applying Stray Light Correction
This instrument only In-Range stray light correction between 280 and 390 nm
Linear corrected and normalized signal [counts/ms]
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Responsitity
Measuring standard lamp
Using same procedure as above:
- Linear correction of raw signal and dark measurements
- Stray light correction
Calculate responsivity in [counts/ms -> measured / (W/m2 /nm) -> known lamp]
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Final spectrum
Measurements (counts/ms ) divided by responsivity
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Final spectrum
Measurements (counts/ms ) divided by responsivity
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Bandwith and Wavelength Homegenization
Problem:
- Irregular grid of wavelength from array spectroradiometer
- Shift of wavelength (non ideal characterization pixel – wavelength)
- Variable slit functions on array spectroradiometer depending on wavelength
Objective:
- Regular grid of wavelengths (no splining!)
- Correction for Wavelength-Shift
- Nominal slit function for all wavelengths instead of variable slit functions from
array spectroradiometer
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Matshic
1. Extra-Terrestrial Spectrum ET (MHP-COKITH)
- wavelength step 0.01 nm, bandwidth 0.05 nm (Validated from 290 – 500 nm)
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Matshic
1. Extra-Terrestrial Spectrum ET (MHP-COKITH)
- wavelength step 0.01 nm, bandwidth 0.05 nm (Validated from 290 – 500 nm)
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Matshic
2. Relation between ET and measured Spectrum
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Matshic
2. Relation between ET and measured Spectrum
Wavelenght Space
Irradiance Level
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Matshic - Procedure
a) convoluting ET - using the instruments (variable) slit function
b) determine O3 attenuation
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Matshic - Procedure
a) comparison of measured spectrum with processed ET
b) shift the ET for wavelength in 0.005 nm step.
c) determine the best congruence of measurements with ET for all wavelengths-steps and all wavelength of the array spectroradiometer
d) applying the best wavelength shift to the ET
e) applying measured irradiance scale to the ET with selectable:
bandwidth & wavelength grid
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Matshic Results
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Matshic Result
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Matshic in Matlab
Data-In: Matlab Matrix or ASCII (in uvdata)
Slit- function (variable or single slit)
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Matshic in Matlab
Main -Configuration:
- ET
- WL-shift-range
- Analysing window for WL-Shift
- Bandwidth of output spectrum
- Format in and out (ASCII or Matlab)
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Matshic in Matlab
Location -Configuration:
- Latitude and Longitude
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Matshic in Matlab
Instrument-Configuration:
- criteria individually for each inst. (-debug 2)
- wl-range of output spectrum
- using single slit (if variable is available)
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Matshic in Matlab
Running Matshic:
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Result
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Conclusion
For array spectroradiometer data post-processing is
important and should be tailored individually to the specific instrument.
- integration times
- linear correction
- stray light correction
- wavelength shift detection
Matshic provides bandwidth and wavelength homogenized spectra – to be compared with other instruments
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Discussion – Experience of othe Users