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Volume 11, issue 4 | Copyright

Special issue: CALIPSO version 4 algorithms and data products

Atmos. Meas. Tech., 11, 2485-2500, 2018
https://doi.org/10.5194/amt-11-2485-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Apr 2018

Research article | 27 Apr 2018

CALIPSO IIR Version 2 Level 1b calibrated radiances: analysis and reduction of residual biases in the Northern Hemisphere

Anne Garnier1,2, Thierry Trémas3, Jacques Pelon4, Kam-Pui Lee1,2, Delphine Nobileau5, Lydwine Gross-Colzy5, Nicolas Pascal6, Pascale Ferrage3, and Noëlle A. Scott7 Anne Garnier et al.
  • 1Science Systems and Applications, Inc., Hampton, VA 23666, USA
  • 2NASA Langley Research Center, Hampton, VA 23681, USA
  • 3Centre National d'Études Spatiales, Toulouse, 31401, France
  • 4Laboratoire Atmosphères, Milieux, Observations Spatiales, Sorbonne Université, CNRS, Paris, 75252, France
  • 5Cagpemini Technology Services, Toulouse, 31086, France
  • 6Hygeos, AERIS/ICARE Data and Services Center, Lille, 59650, France
  • 7Laboratoire de Météorologie Dynamique, Ecole Polytechnique-CNRS, Palaiseau, 91128, France

Abstract. Version 2 of the Level 1b calibrated radiances of the Imaging Infrared Radiometer (IIR) on board the Cloud-Aerosol Lidar and Infrared Satellite Observation (CALIPSO) satellite has been released recently. This new version incorporates corrections of small but systematic seasonal calibration biases previously revealed in Version 1 data products mostly north of 30°N. These biases – of different amplitudes in the three IIR channels 8.65µm (IIR1), 10.6µm (IIR2), and 12.05µm (IIR3) – were made apparent by a striping effect in images of IIR inter-channel brightness temperature differences (BTDs) and through seasonal warm biases of nighttime IIR brightness temperatures in the 30–60°N latitude range. The latter were highlighted through observed and simulated comparisons with similar channels of the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Aqua spacecraft. To characterize the calibration biases affecting Version 1 data, a semi-empirical approach is developed, which is based on the in-depth analysis of the IIR internal calibration procedure in conjunction with observations such as statistical comparisons with similar MODIS/Aqua channels. Two types of calibration biases are revealed: an equalization bias affecting part of the individual IIR images and a global bias affecting the radiometric level of each image. These biases are observed only when the temperature of the instrument increases, and they are found to be functions of elapsed time since night-to-day transition, regardless of the season. Correction coefficients of Version 1 radiances could thus be defined and implemented in the Version 2 code. As a result, the striping effect seen in Version 1 is significantly attenuated in Version 2. Systematic discrepancies between nighttime and daytime IIR–MODIS BTDs in the 30–60°N latitude range in summer are reduced from 0.2K in Version 1 to 0.1K in Version 2 for IIR1–MODIS29. For IIR2–MODIS31 and IIR3–MODIS32, they are reduced from 0.4K to close to zero, except for IIR3–MODIS32 in June, where the night-minus-day difference is around −0.1K.

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Residual calibration biases affecting CALIPSO IIR Version 1 calibrated radiances in the Northern Hemisphere are analyzed and reduced through in-depth analysis of the IIR internal calibration procedure in conjunction with observations such as statistical comparisons with similar MODIS/Aqua channels.
Residual calibration biases affecting CALIPSO IIR Version 1 calibrated radiances in the Northern...
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