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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-345
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Nov 2016
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.
Long term assessment of the CALIPSO Imaging Infrared Radiometer (IIR) calibration and stability through comparisons with MODIS/Aqua and SEVIRI/Meteosat
Anne Garnier1,2, Noëlle A. Scott3, Jacques Pelon4, Raymond Armante3, Laurent Crépeau3, Bruno Six5, and Nicolas Pascal6 1Science Systems and Applications, Inc., Hampton, VA 23666, USA
2NASA Langley Research Center, Hampton, VA 23681, USA
3Laboratoire de Météorologie Dynamique, Ecole Polytechnique-CNRS, Palaiseau, 91128, France
4Laboratoire Atmosphères, Milieux, Observations Spatiales, UPMC-UVSQ-CNRS, Paris, 75252, France
5Université Lille 1, AERIS/ICARE Data and Services Center, Lille, 59650, France
6Hygeos, AERIS/ICARE Data and Services Center, Lille, 59650, France
Abstract. The quality of the calibrated radiances of the medium-resolution Imaging Infrared Radiometer (IIR) on-board the CALIPSO satellite is quantitatively controlled since the beginning of the mission in June 2006. Two complementary “relative” and “stand-alone” approaches are used, which are related to comparisons of measured brightness temperatures, and to model-to-observations comparisons, respectively. In both cases, IIR channels 1 (8.65 μm), 2 (10.6 μm), and 3 (12.05 μm) are paired with MODIS/Aqua “companion” channels 29, 31, and 32, respectively, as well as with SEVIRI/Meteosat companion channels IR8.7, IR10.8 and IR12, respectively. These pairs were selected before launch to meet radiometric, geometric and space-time constraints. The pre-launch studies were based on simulations and sensitivity studies using the 4A/OP radiative transfer model fed with the more than 2300 atmospheres of the climatological TIGR dataset further sorted out in five air mass types. Over the 9.5 years of operation since launch, in a semi-operational process, collocated measurements of IIR and of its companion channels have been compared at all latitudes over ocean, during day and night, and for all types of scenes in a wide range of brightness temperatures when dealing with the relative approach. The relative approach shows an excellent stability of IIR2-MODIS31 and IIR3-MODIS32 brightness temperature differences (BTD) since launch A slight trend of the IIR1-MODIS29 BTD, equal to −0.02 K/year on average over 9.5 years, is detected by the relative approach at all latitudes and all scene temperatures. For the stand-alone approach, clear sky measurements only are considered, which are directly compared with simulations using 4A/OP and collocated ERA-Interim reanalyses. The clear sky mask is derived from collocated observations from IIR and the CALIPSO lidar. Simulations for clear sky pixels in the tropics reproduce the differences between IIR1 and MODIS29 within 0.02 K, and between IIR2 and MODIS31 within 0.04 K, whereas IIR3-MODIS32 is larger than simulated by 0.26 K. The stand-alone approach indicates that the trend identified from the relative approach originates from MODIS29, whereas no trend (less than ±0.004 K/year) is evidenced for any of the IIR channels. Finally, a year-by-year seasonal bias between nighttime and daytime IIR-MODIS BTDs was found at mid-latitude in the northern hemisphere by the relative approach. It is due to a nighttime IIR bias as determined by the stand-alone approach, which originates from a calibration drift during day-to-night transitions. The largest bias is in June/July with IIR2 and IIR3 too warm by 0.4 K on average, and IIR1 too warm by 0.2 K.

Citation: Garnier, A., Scott, N. A., Pelon, J., Armante, R., Crépeau, L., Six, B., and Pascal, N.: Long term assessment of the CALIPSO Imaging Infrared Radiometer (IIR) calibration and stability through comparisons with MODIS/Aqua and SEVIRI/Meteosat, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-345, in review, 2016.
Anne Garnier et al.
Anne Garnier et al.

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Short summary
An assessment of IIR radiances after 9.5 years of nearly continuous operation since June 2006 is presented. First, IIR is compared with MODIS or SEVIRI similar channels in various conditions. Secondly, clear sky measurements in each channel are compared with simulations. The first approach detects biases and/or trends, and the second approach contributes to identify which channel deviates from the other. The analyses are based on simulations using the 4A/OP radiative transfer model.
An assessment of IIR radiances after 9.5 years of nearly continuous operation since June 2006 is...
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