Fail Min
Known in data files as “Valid Min” and in DQ Explorer as “Fail Min,” this is the minimum allowable value that a measurement can have. This can give false positives as instrument noise can sometimes cause data to go over the threshold.
Fail Max
Known in data files as “Valid Max” and in DQ Explorer as “Fail Max,” this is the maximum allowable value that a measurement can have. This can give false positives as instrument noise can sometimes cause data to go over the threshold.
Fail Delta
Known in data files as “Valid Delta” and in DQ Explorer as “Fail Delta,” this is the minimum allowable value that a measurement can change between 2 samples. Indeterminate as some data can have sharp changes over short periods of time.
Embedded quality control (QC) fields use bit-packing (a way to compress data) to store the results from multiple QC tests that may be used for a datastream into a single QC field. They are a representation of true/false values for the tests that may be performed. Each datastream describes the QC tests performed on the data values in the netCDF header of the datastream, which includes a description of the bit number correlating to the test. If a datastream has four tests performed on the data, for example, then each bit will be described with a description attribute in the netCDF header that describes the test associated with each bit. If a value meets the test criteria (a value is higher than the valid maximum, etc.), then that bit will be set.
The following is a non-exhaustive list. Examples of some DQO QC bits you may come across include:
Data value is negative
This bit will be set if a data value is negative.
Value is less than the fail_min
This bit will be set if a data value is less than the valid minimum allowed for the data.
Value is greater than the fail_max
This bit will be set if a data value is more than the valid maximum allowed for the data.
Value is equal to missing_value
This bit will be set if a data value is missing (typically, missing values are set to -9999).
There are several other QC bits used depending on the instrument and datastream in question. While it is not important to know all of the details regarding how the bit-packing in the embedded QC fields work, it is helpful to have a general idea of when (and why) different DQO QC bits may be set.