Improved cloud detection in AVHRR daytime and nighttime scenes over the ocean

Accurate cloud detection is needed for many geophysical applications. Unfortunately, a significant source of residual error in such satellite-based products is undetected cloud. Here, a new, computationally efficient cloud detection procedure for both daytime and nighttime Advanced Very High Resolution Radiometer (AVHRR) data is developed. It differs substantially from our prior related work. First, a new clustering procedure is used which produces very homogeneous and distinct clusters. Second, the input information vector is reduced in size, incorporates both radiance and spatial components and each component is normalized. Third, the enhanced performance makes possible the use of a multipass procedure which is very effective in identifying the complex multilayer cloud structures common in satellite data. Validation with independent lidar observations confirms the accuracy of the new procedure. Marine low stratiform clouds (fog, stratus and stratocumulus) also are detected effectively.