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Arctic cloud detection by means of hyperspectral infrared interferometry (HyperACD)
Call year: 2015
Status: active
IADC_id: 14
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Project description:
Clouds play a key role on the radiation budget of the Earth. However, the polar cloud feedback in climate sensitivity remains poorly understood. Polar satellite measurements provide frequent revisit over the Arctic, but cloud detection is challenging at high latitudes. In fact, the ability to detect cloud presence from passive satellite measurements in the polar regions is complicated by little thermal and visible contrast between clouds and snow/ice surface, persistence of atmospheric temperature inversion, low optical thickness, presence of mixed-phase clouds, low signal-to-noise ratios. During polar nights, cloud detection is even more difficult, because techniques based on texture or differential reflectance in the visible and near infrared are not usable. A variety of threshold methods based on multi- and hyper-spectral observations have been proposed recently, although problems still exists with thin clouds and weak inversions. In addition, uncertainties related to surface emissivity play an important role, since spectral emissivity for ice/snow surfaces may differ significantly depending upon microphysical properties. Thus, we propose to analyze currently available techniques and develop modifications based on simulated radiances using realistic sea/ice/snow emissivity spectra. We propose to validate the new technique using nearly simultaneous observations from satellite active sensors and ground-based instruments from few sites in the Arctic, including Ny-Ålesund.
National/International Cooperation:
A collaboration is ongoing with Christoph Ritter and Marion Maturilli of Alfred-Wegener-Institut (Germany) who are responsible for some of the instruments running at the GCOS Reference Upper Air Network site in Ny-Ålesund.
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