Here we discuss how pwv_kpno handles the parsing of raw SuomiNet data. While this is not technically part of the validation process, the design decisions outlined here have a direct effect on the various values and errors reported by the package.
Standard SuomiNet data files are published with PWV and PWV error values recorded to a one decimal point precision. Unfortunately, the error in PWV can sometimes be less than 0.05. As a result, the SuomiNet data pipeline will round the error in these measurements down to zero. To account for this loss of information, pwv_kpno adds a conservative 0.025 error to all downloaded PWV measurements.
In very rare instances, SuomiNet data files may contain two measurements for a given location and datetime that are unequal. Since there is no way to determine from the data files which value is correct, pwv_kpno ignores both entries. In the case where there are multiple datetime entries with the same measurements, these entries are kept.
In the published SuomiNet data there are occasional instances when the measured PWV column density is unmasked and negative. In some (but not necessarily all) cases this can be attributed to a hardware malfunction. Measurements for any time when the reported PWV concentration is negative are ignored.
For GPS sites located within the continental United States, SuomiNet measurements are published hourly and then reprocessed and published again daily. Although the hourly data releases are convenient, they are not necessarily as accurate as the daily releases. As such pwv_kpno uses measurements from the daily data releases whenever possible and supplements these measurements with the hourly releases when daily data is not available.