Day 4

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Paper title The ATLID-MSI synergy – Extending vertical information from the track to the swath
  1. Moritz Haarig Leibniz Institute for Tropospheric Research (TROPOS) Speaker
  2. Anja Hünerbein Leibniz Institute for Tropospheric Research (TROPOS)
  3. Ulla Wandinger TROPOS
  4. Nicole Docter Freie Universität Berlin
  5. Rene Preusker Freie Universität Berlin (FUB)
  6. Sebastian Bley Leibniz Institute for Tropospheric Research (TROPOS)
  7. David Patrick Donovan Royal Netherlands Meteorological Institute (KNMI)
  8. Gerd-Jan van Zadelhoff Royal Netherlands Meteorological Institute (KNMI)
Form of presentation Poster
  • A1. Atmosphere
    • A1.09 EarthCARE: Preparing for the Scientific Mission Exploitation to Quantify the Impact of Clouds and Aerosols on Radiation
Abstract text The great benefit of EarthCARE for the global observation of the atmosphere lies in its synergistic approach of combining four instruments on one single platform. The two active instruments ATLID (atmospheric lidar) and CPR (cloud profiling radar) deliver vertical profiles of aerosol and cloud properties. The two passive instruments BBR (broad band radiometer) and MSI (multispectral imager) extend the information by adding observations of the total and shortwave radiation at top of atmosphere (BBR) and spectral radiances at the across track swath (MSI).
The systematic combination of active and passive remote sensing on a single platform is new and offers us great opportunities for synergistic retrieval approaches. Here, we will focus on the synergy of the vertical profiles measured with ATLID (‘curtain’) and the horizontal information added by the MSI (‘carpet’) to provide a more complete picture of the observed scene. For this purpose, the synergistic ATLID-MSI columnar descriptor AM-COL was developed in the EarthCARE processing chain. The MSI input is provided by the MSI cloud (M-CLD) and MSI aerosol (M-AOT) processor, the ATLID input is calculated by the ATLID layer processor (A-LAY). Cloud and aerosol information derived on the track are combined from both instruments and the additional ATLID information is transferred to the swath using the MSI observations. Two main results will be described in the following paragraphs, the cloud top height and the Ångström exponent.
The difference of the cloud top height measured with ATLID and retrieved from MSI is calculated along track. The obtained differences are transferred to the swath searching for similar nearby MSI pixels. Five homogeneity criteria are used: same cloud type, same cloud phase and surface type, the reflectivity at 0.67 µm and the brightness temperature at 10.8 µm. At nighttime, only a reduced set of criteria can be used (no cloud type and no reflectivity differences are available). Multilayer cloud scenarios have to be treated with special care and are investigated separately. Especially, thin cirrus clouds above liquid-containing clouds are hardly detectable with MSI.
The three simulated test scenes developed for EarthCARE are intensively used to test the algorithm performance. In case of the mixed-phase clouds and some thick cirrus clouds present in the so-called ‘Halifax’ scene, the difference between ATLID and MSI is found to be smaller than 1000 m. When looking at multilayer clouds or large convective systems this difference increases. For homogeneous cloud coverage, the transfer of the cloud top height difference to the swath can be easily applied. The test scenes offer the possibility to check the transfer to the swath for the more complicated multilayer scenes as well. The comparison to the model truth lets us estimate the performance of the synergistic product and provides an estimation for the detection limits when it comes to real data.
The aerosol optical properties are obtained at 670 nm and 865 nm (ocean only) by MSI and at 355 nm by ATLID. The ATLID-MSI synergy enables us to calculate the Ångström exponent (355/670 and 355/865) along track adding spectral information to the single wavelength lidar ATLID. The Ångström exponent adds additional information to the aerosol typing. Along the nadir track we can combine the vertical resolved aerosol classification from ATLID with the aerosol typing included in the MSI retrieval. Knowing the aerosol type along track seen by both ATLID and MSI enables us to transfer the aerosol information to the swath using the MSI measurements. For this purpose, an explicit aerosol test scene was developed additionally to the three standard EarthCARE test scenes. It could be shown that the MSI-based aerosol typing agrees with the columnar aerosol classification probabilities derived from ATLID for this scene.