What is the purpose of the rain_impact variable in the Version 2, 3 and 4 QuikSCAT L2B datasets?
The rain_impact variable is a product of the IMUDH rain detection and flagging algorithm as documented here: ftp://podaac.jpl.nasa.gov/allData/quiks ... ion_V3.pdf. The primary purpose of the rain_impact variable is to provide a determinative threshold which is used to set bit 13 of the flag (wvc_quality_flag) variable which determines whether or not rain is detected, thus setting the rain flag. Once this rain flag is set, the rain correction is applied to the "retrieved_wind_speed" variable in the Version 3 and 4 datasets (no rain corrections are applied in the Version 2 dataset). Although there may be other reasons why someone may want to use the rain_impact variable, it's generally recommended for expert use only.