The parameter masking operation (mapmask) will apply one or more masks or filters on the selected parameters. If no masks are defined for a parameter then this step is skipped. There are two types of masks that may be applied: dynamic user supplied and mandatory. This step may be invoked by any of the Giovanni services.
The dynamic (user-supplied) mask is specified by the user from the Giovanni interface. If the user does not specify a value, the system will use a set of defaults.
- mask out data values over land;
- filter the data based on cloud fraction less than 30%.
Mandatory masks or filters are set by Giovanni, and the user cannot change these values. An example is to filter data based on a science team recommendation that users not use data where a quality flag is outside a particular range.
Data values which have been masked will be set to the parameter's fill value, and thus will be excluded from any calculations in subsequent analysis steps.