VIIRS Edition 1 Cloud Properties for CERES, Part 1: Algorithm Adjustments and Results

Cloud properties are essential for the Clouds and the Earth's Radiant Energy System (CERES) Project, enabling accurate interpretation of measured broadband radiances, providing a means to understand global cloud-radiation interactions, and constituting an important climate record. Producing consistent cloud retrievals across multiple platforms is critical for generating a multidecadal cloud and radiation record. Techniques used by CERES for retrievals from measurements by the MODerate-Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua platforms are adapted for the application to radiances from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership to continue the CERES record beyond the MODIS era. The algorithm adjustments account for spectral and channel differences, use revised reflectance models, and set new thresholds for detecting thin cirrus clouds at night. Cloud amounts from VIIRS are less than their MODIS counterparts by 0.016 during the day and 0.026 at night, but trend consistently over the 2012-2020 period. The VIIRS mean liquid water cloud fraction differs by similar to 0.01 from the MODIS amount. The average cloud heights from VIIRS differ from the MODIS heights by less than 0.2 km, except the VIIRS daytime ice cloud heights, which are 0.4 km higher. The mean VIIRS nonpolar optical depths are 17% (1%) larger (smaller) than those from MODIS for liquid (ice) clouds. The VIIRS cloud hydrometeor sizes are generally smaller than their MODIS counterparts. Discrepancies between the MODIS and VIIRS properties stem from spectral and spatial resolution differences, new tests at night, calibration inconsistencies, and new reflectance models. Many of those differences will be addressed in future editions.

Automated summary

Cloud properties are crucial for the CERES Project as they allow accurate interpretation of measured radiances, understanding of global cloud-radiation interactions, and establishment of an important climate record. The CERES techniques for cloud retrievals from MODIS measurements have been adapted for VIIRS measurements to continue the record. There are discrepancies between MODIS and VIIRS cloud properties due to differences in spectral and spatial resolution, calibration inconsistencies, and new reflectance models.