The MODIS Cloud Optical Thickness layer is a measure of the amount of sunlight affected by absorption and scattering when passing through the clouds. Clouds scatter and reflect most visible light. Hence it is simultaneously retrieved with Cloud Effective Radius by simultaneously measuring the reflection function of a non-absorbing and absorbing spectral channel (e.g., Visible/Near Infrared (VIS/NIR) and Shortwave Infrared (SWIR), respectively) and comparing the resulting measurements with theoretical forward model calculations. This layer is the the Cloud Optical Thickness PCL (partly cloudy) retrieval using Band 7 (2.1 μm) for pixels classified as either partly cloudy from 250 m cloud mask test or 1 km cloud edges.

The MODIS Cloud Optical Thickness layers available are: the Cloud Optical Thickness retrieval using Band 7 (2.1 μm); (2) the Cloud Optical Thickness PCL (partly cloudy) retrieval using Band 7 (2.1 μm) for pixels classified as either partly cloudy from 250 m cloud mask test or 1 km cloud edges.

The MODIS Cloud Optical Thickness layers are available from both the Terra (MOD06) and Aqua (MYD06) satellites for daytime overpasses. The sensor/algorithm resolution is 1 km, imagery resolution is 1 km, and the temporal resolution is daily.

References: MODIS Atmosphere - Cloud (06_L2); NEO Cloud Optical Thickness; MODIS Cloud Optical Properties: User Guide for the Collection 6 Level-2 MOD06/MYD06 Product and Associated Level-3 Datasets: July 2018; Cloud Top Properties and Cloud Phase Algorithm Theoretical Basis Document: May 2015