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@ARTICLE{Bohn:828469,
      author       = {Bohn, Birger and Lohse, Insa},
      title        = {{C}alibration and evaluation of {CCD} spectroradiometers
                      for airborne measurements of spectral actinic flux
                      densities},
      journal      = {Atmospheric measurement techniques discussions},
      volume       = {},
      issn         = {1867-8610},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2017-02428},
      pages        = {1 - 31},
      year         = {2017},
      abstract     = {The properties and performance of CCD array
                      spectroradiometers for the measurement of atmospheric
                      spectral actinic flux densities and photolysis frequencies
                      were investigated. These instruments are widely used in
                      atmospheric research and are suitable for aircraft
                      applications because of high time resolutions and high
                      sensitivities in the UV range. The laboratory
                      characterization included instrument-specific properties
                      like wavelength accuracy, dark signals, dark noise and
                      signal-to-noise ratios. Spectral sensitivities were derived
                      from measurements with spectral irradiance standards. The
                      calibration procedure is described in detail and a
                      straightforward method to minimize the influence of stray
                      light on spectral sensitivities is introduced. Detection
                      limits around 1×1010cm−2 s−1 nm−1 were derived for
                      spectral actinic flux densities in a 300 nm range (1 s
                      integration time). As a prerequisite for the determination
                      of stray light under field conditions, atmospheric cutoff
                      wavelengths were defined using radiative transfer
                      calculations as a function of solar zenith angles and ozone
                      columns. The recommended analysis of field data relies on
                      these cutoff wavelengths and is also described in detail
                      taking data from a research flight as an example. An
                      evaluation of field data was performed by ground-based
                      comparisons with a double-monochromator reference
                      spectroradiometer. Spectral actinic flux densities were
                      compared as well as photolysis frequencies j(NO2) and
                      j(O1D), representing UV-A and UV-B ranges, respectively. The
                      spectra expectedly revealed an increased daytime level of
                      residual noise below atmospheric cutoff wavelengths that is
                      caused by stray light. The influence of instrument noise and
                      stray light induced noise was found to be insignificant for
                      j(NO2) and rather limited for j(O1D), resulting in estimated
                      detection limits of 5×10−7 s−1 and 1×10−7 s−1,
                      respectively. For j(O1D) the detection limit could be
                      further reduced by setting spectral actinic flux densities
                      below cutoff wavelengths to zero. The accuracies of
                      photolysis frequencies were determined from linear
                      regressions with reference instrument data. The agreement
                      was typically within ±5 $\%.$ Optical receiver aspects were
                      widely excluded in this work and will be treated in a
                      separate paper in particular with regard to airborne
                      applications. Overall, the investigated instruments are
                      clearly suitable for high quality photolysis frequency
                      measurements with high time resolution as required for
                      airborne applications. An example of data from a flight on
                      the research aircraft HALO is presented.},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {243 - Tropospheric trace substances and their
                      transformation processes (POF3-243)},
      pid          = {G:(DE-HGF)POF3-243},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.5194/amt-2017-74},
      url          = {https://juser.fz-juelich.de/record/828469},
}