The operational MODIS cloud optical and microphysical retrieval product: Overview of the Collection 5 processing algorithm and preliminary Level-2 results

Operational Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of cloud optical and microphysical properties (part of the archived products MOD06 and MYD06, for MODIS Terra and Aqua, respectively) are currently being reprocessed along with the other MODIS Atmosphere Team products. This so-called “Collection 5” processing stream, which is expected to be completed by year's end, includes updates to the previous cloud retrieval algorithm along with new capabilities.

The 1 km retrievals, based on well-known solar reflectance techniques, include cloud optical thickness, effective particle radius, and water path, as well as thermodynamic phase derived from a combination of solar and infrared tests. Being both global and of high spatial resolution requires an algorithm that is computationally efficient and can perform over all surface types. Collection 5 additions include the development and use of spatially-complete global spectral surface albedo maps derived from MODIS, pixel-level uncertainties incorporating fundamental error sources, and the use of additional spectral and spatial tests to help eliminate false cloud detection (e.g., dust, snow/ice, sun glint) and partly-cloudy pixels. Results from a research-level multi-layer cloud detection algorithm are also included.

We will summarize the Collection 5 changes and discuss example retrievals obtained from the archive. The emphasis will be on pixel-level (Level-2) retrievals, but implications for the gridded (Level-3) product will also be discussed.