The MODIS Cloud Effective Radius layer is a measure of cloud particle size in microns (μm). It is retrieved globally during day time for liquid and ice phases. This layer is the Cloud Effective Radius 3.7 micron PCL (partly cloudy) layer retrieval using Band 20 (3.7 μm) for pixels classified as either partly cloudy from 250 m cloud mask test or 1 km cloud edges. It is simultaneously retrieved with Cloud Optical Thickness 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. Generally, smaller the particle size, brighter and more reflective are the clouds. The smaller cloud particles tend to reflect and scatter more sunlight back into space.

The MODIS Cloud Particle Effective Radius layers available are: (1) the Cloud Effective Radius retrieval using Band 7 (2.1 μm); (2) the Cloud Effective Radius 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; (3) the Cloud Effective Radius 3.7 micron layer retrieval using Band 20 (3.7 μm); and (4) the Cloud Effective Radius 3.7 micron PCL layer retrieval using Band 20 (3.7 μm) for pixels classified as either partly cloudy from 250 m cloud mask test or 1 km cloud edges.

The MODIS Cloud Effective Radius 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); 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