When one data variable provides metadata about the individual values
of another data variable it may be desirable to express this association
by providing a link between the variables. For example, instrument data
may have associated measures of uncertainty. The attribute
ancillary_variables is used to express these types of
relationships. It is a string attribute whose value is a blank separated
list of variable names. The nature of the relationship between variables
associated via ancillary_variables must be determined
by other attributes. The variables listed by the
ancillary_variables attribute will often have the
standard name of the variable which points to them including a modifier
(Appendix C, Standard Name Modifiers) to indicate the
relationship.
Example 3.2. Instrument data
float q(time) ;
q:standard_name = "specific_humidity" ;
q:units = "g/g" ;
q:ancillary_variables = "q_error_limit q_detection_limit" ;
float q_error_limit(time)
q_error_limit:standard_name = "specific_humidity standard_error" ;
q_error_limit:units = "g/g" ;
float q_detection_limit(time)
q_detection_limit:standard_name = "specific_humidity detection_minimum" ;
q_detection_limit:units = "g/g" ;