What factors affect the quality of salinity retrievals from Aquarius, how may this vary regionally and what documentation exists on these aspects?
Numerous factors can influence geophysical retrieval of salinity from Aquarius, including land and galactic contamination, radio-frequency interference (RFI), rain and high wind effects that affect the back-scatter signal, and the state of the instruments themselves. All of these factors, potentially in combination, influence the quality of the Aquarius salinity data and may be manifest as regional differences in accuracy and uncertainty. The state of all such mitigating factors is measured and captured in the Level 2 Aquarius swath data files as quality flags together with the geophysical variables themselves, corresponding observation times and orbital geo-reference data. Details on the Aquarius L2 quality flag settings, flagging variables and data files are available in the Aquarius Data Users Guide. These quality flags can be used to filter out retrieved salinity values that may have been compromised by one or more of these impeding factors being present above some threshold level. This is important to do prior to usage for analysis, and the specific quality flags applied may vary somewhat between applications or for specific usages. The set of flags and masks applied in the creation of the Aquarius Level 3 gridded/mapped products from L2 data are also described in the Aquarius Data User's. These have been selected to, overall and as best possible, both maximize the quality and coverage of the mapped, 1 degree spatial resolution L3 data. Level 3 data users may notice, however, some locales that are less well covered or where remotely sensed salinity values may differ slightly from expectation based on field measurements. If the area of interest is within one degree of land, most likely the missing values are because of possible land contamination. Of course, other possible sources of missing data include RFI, rain effects, and other flags which are set or used to mask out data under moderate to severe conditions. For more details it is recommended the user read the Aquarius Salinity Data Validation Analysis document, Users Guide, and other more detailed documentation dealing with flags used in the salinity retrieval calculation and calibration. These documents are available at https://podaac-tools.jpl.nasa.gov/drive ... arius/docs. Specific references to regional and seasonal dependencies of data quality and errors may also be found in the Aquarius Validation Analysis document.