Clear Sky Mask

Background

For many of the other products, it is important to determine which portions of the sky have clouds and which do not. More fornally, the Clear Sky Mask product provides the location of the cloud free vertical columns of the atmosphere. Hhile the official product is the Clear Sky Mask, the location of clouds is also important. This "Cloud Mask" is not a "product" because it is just the opposite values from the Clear Sky Mask. Expressed most simply, the Clear Sky Mask identifies every as clear or not clear. The cloud mask does not need to be a distinct product since every "not clear" location is a "cloud" and every "clear" location is "not a cloud".

Product Description

Cloud detection is the process of separating cloudy from clear pixels. It always involves assumptions of the radiometric characteristics of the clear and/or cloudy state and looking for departures from them. In the ACM, spectral, spatial and temporal tests are used to look for clouds by identifying pixels that do not exhibit the expected behavior of the clear-sky state. Each test described is applied to each pixel, resulting in a cloud/no cloud score, which is then used to decide whether a pixel is cloudy or clear.

Improvements and Benefits

The Clear Sky Mask algorithm will take advantage of the high spatial and temporal resolution of the GOES-R ABI visible, near-infrared, and infrared bands to automatically produce a cloud classification for each pixel: cloudy, probably cloudy, clear, or probably clear. This information will be used extensively by downstream level-2 product algorithms that require the state of cloudiness in each pixel. Products such as Land Surface Temperature (LST) and Sea Surface Temperature (SST), for example, can only be reliably computed for pixels that are totally cloud free. The Clear Sky Mask product can be used by the NWP community to identify which ABI pixel information should be assimilated for use in numerical weather prediction models.