Question: Why am I seeing CYGNSS Level 2 MSS (mean-square-slope) values above the valid range upper limit as defined in the netCDF variable attributes?
Answer: The MSS valid range as defined in the netCDF variable attributes is based on a theoretical range that was pre-determined before the CYGNSS observed MSS was computed. MSS observed by CYGNSS, depending on the underlying calibrations and algorithms used in various versions of Level 2 (i.e., SDR v2.1 and v3.0; CDR v1.0 and v1.1), in some cases will exceed this predefined limit, as there is no quality control (QC) in place that limits the upper limit of MSS as computed in the CYGNSS data files. As a general rule, regardless of which product of CYGNSS Level 2 data is being used, users are advised to discard MSS values exceeding 0.1, as this is considered the physical upper limit of MSS in real-world ocean conditions. Future versions of CYGNSS data will employ a QC filtering step to ensure that the observed MSS does not exceed the defined upper limit.