Abstract
Abstract. Retrieval of semitransparent ice cloud properties from the Visible Infrared Imaging Radiometer Suite (VIIRS) satellite sensor on the Suomi National Polar-orbiting Partnership (S-NPP) and NOAA-20 platforms is challenging due to the absence of infrared (IR) water vapor and CO2 absorption channels. However, on these platforms, there is a companion sensor called the Crosstrack Infrared Sounder (CrIS) that provides these spectral measurements but at a lower spatial resolution (∼15 km at nadir). To mitigate the lack of VIIRS spectral measurements in these IR absorption channels, recent studies suggest an approach to supplement VIIRS measurements by fusion of the imager and sounder data. In particular, Weisz et al. (2017) demonstrate a method to construct IR water vapor and CO2 absorption channel radiances for VIIRS at 750 m spatial resolution. Based on these constructed channels for both S-NPP and NOAA-20, this study evaluates three cloud properties – cloud mask, cloud thermodynamic phase, and cloud top height – through comparison to the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation/Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO/CALIOP) V4-20 cloud layer products and Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6.1 cloud top products. Each of these cloud properties shows improvement with the use of these constructed channel radiances. The major improvement for the cloud mask is found over polar regions, where the correct cloud detection percentage increases due to a decrease in missed clouds and/or false detection. For cloud thermodynamic phase, the ice cloud fraction increases over non-polar regions and the combined liquid water and ice cloud discrimination improves in comparison with CALIPSO. The retrieved cloud top height for semitransparent ice clouds increases over non-polar regions and tends to be closer to the true CALIPSO/CALIOP cloud top height. Moreover, the uncertainty of cloud top height retrievals decreases globally for these clouds.
Highlights
Current polar-orbiting satellite imager sensors, such as the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard both the Suomi National Polar-orbiting Partnership (S-NPP) and the National Oceanic and Atmospheric Administration-20 (NOAA-20), have many advantages compared to previous-generation imagers, such as a wider scanning swath, a pixel size that varies little across the scan, and the addition of a day/night band (DNB)
The 15 μm channels are used in the CO2 slicing approach that was implemented in the National Aeronautics and Space Administration’s (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) products (Menzel et al, 2008; Baum et al, 2012) and High resolution Infrared Radiometer Sounder (HIRS) products
The absence of water vapor and CO2 absorption IR channels on the VIIRS imager on the S-NPP and NOAA-20 polar-orbiting platforms limits the capability for cloud property retrievals, especially for retrievals involving semitransparent ice clouds
Summary
Current polar-orbiting satellite imager sensors, such as the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard both the Suomi National Polar-orbiting Partnership (S-NPP) and the National Oceanic and Atmospheric Administration-20 (NOAA-20), have many advantages compared to previous-generation imagers, such as a wider scanning swath, a pixel size that varies little across the scan, and the addition of a day/night band (DNB). The absence of certain thermal infrared (IR) bands makes it challenging to accurately retrieve cloud properties that are dependent on those spectral measurements. Y. Li et al.: VIIRS+CrIS fusion cloud properties (Menzel et al, 2016). Li et al.: VIIRS+CrIS fusion cloud properties (Menzel et al, 2016) These IR channels are available on the hyperspectral IR sensor called the Crosstrack Infrared Sounder (CrIS), on the S-NPP and NOAA-20 platforms. A sounding sensor is used for retrieving accurate atmospheric temperature and moisture profiles based on its hyperspectral coverage but at a lower spatial resolution than an imager such as VIIRS. The products from the CrIS sounder show significant enhancement over NOAA’s legacy HIRS sensors
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