Assessment of the Quality of MODIS Cloud Products from Radiance Simulations

• Published in: Journal of applied meteorology and climatology 2009-08, Vol.48 (8), p.1591-1612
• Main Authors: Ham, Seung-Hee, Sohn, Byung-Ju, Yang, Ping, Baum, Bryan A.
• Format: Article
• Language: English
• Subjects: Absorption bands; Absorption spectra; Accuracy; Aerosols; Algorithms; Atmosphere; Atmospheric Infrared Sounder; Bias; CALIPSO (Pathfinder satellite); Carbon dioxide; Cirrus clouds; Cloud computing; Cloud distribution; Cloud observations; Clouds; Cots; Earth observations (from space); Earth, ocean, space; Exact sciences and technology; External geophysics; General circulation models; Greenhouse effect; Humidity profiles; Ice clouds; Lidar; Marine; Meteorology; MODIS; Optical properties; Optical thickness; Particle size; Pixels; Quality assessment; Radiance; Radiation; Radiative transfer; Reflectance; Remote sensing; Satellite observation; Scattering; Short wave radiation; Simulation; Simulations; Spectroradiometers; Vertical distribution; Water vapor; Water vapour
• ISSN: 1558-8424; 1558-8432
• DOI: 10.1175/2009jamc2121.1

Observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS), the Atmospheric Infrared Sounder (AIRS), theCloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), andCloudSatare synergistically used to evaluate the accuracy of theoretical simulations of the radiances at the top of the atmosphere (TOA). Specifically, TOA radiances of 15 MODIS bands are simulated for overcast, optically thick, and single-phase clouds only over the ocean from 60°N to 60°S, corresponding to about 12% of all the MODIS cloud observations. Plane parallel atmosphere is assumed in the simulation by restricting viewing/solar zenith angle to be less than 40°. Input data for the radiative transfer model (RTM) are obtained from the operational MODIS-retrieved cloud optical thickness, effective radius, and cloud-top pressure (converted to height) collocated with the AIRS-retrieved temperature and humidity profiles. In the RTM, ice cloud bulk scattering properties, based on theoretical scattering computations and in situ microphysical data, are used for the radiative transfer simulations. The results show that radiances for shortwave bands between 0.466 and 0.857μm appear to be very accurate with errors on the order of 5%, implying that MODIS cloud parameters provide sufficient information for the radiance simulations. However, simulated radiances for the 1.24-, 1.63-, and 3.78-μm bands do not agree as well with the observed radiances as a result of the use of a single effective radius for a cloud layer that may be vertically inhomogeneous in reality. Furthermore, simulated radiances for the water vapor absorption bands located near 0.93 and 1.38μm show positive biases, whereas the window bands from 8.5 to 12μm show negative biases compared to observations, likely due to the less accurate estimate of cloud-top and cloud-base heights. It is further shown that the accuracies of the simulations for water vapor and window bands can be substantially improved by accounting for the vertical cloud distribution provided by theCALIPSOandCloudSatmeasurements.