Processing BGC-Argo measurement timing information at the DAC level. Version 1.0, March 28th 2017.

Abstract

Thermal lag or sensor time response corrections (e.g., [1]) require knowledge of the time of each individual sensor observation. In the Argo data system, the float's trajectory file is the natural place to put measurement timing information. Historically, only few levels of a float's profile have been timed, and DACs stored these sparse timed levels of the float profile in the trajectory already. Depending on the DAC, all measured paramters are stored with the timing information, or just the PRES variable is stored together with the time. With the need to have all observations timed, this approach leads to the following problems: a) With all parameters stored together with the timing information and put into the trajectory file, the trajectory file in effect duplicates all profiles. This contradicts the Argo data system's design to split profile and trajectory files and may pose a file size issue. b) With only PRES stored together with the timing information and put into the trajectory file, the only link between trajectory timing information and profile parameter observations is through the PRES variable. Due to the potential occurrence of equal PRES values for different parameter observations, this link may be ambiguous. To keep the structure of the Argo data system and to resolve these problems, Biogeochemical-Argo saw a need to be able to store timing information in the float's profile file. Following discussions at ADMT16, AST17, and ADMT17 it was concluded that timing information associated with each measured parameter of the profile is scientifically useful for Biogeochemical-Argo, but does not seem necessary for core Argo. Sparse timing data should remain in the trajectory file – it was designed to handle this data and keeps QC of timing information mostly to one file. Abundant timing information (i.e., timing information for all profile observations), however, are stored in the i-parameter "MTIME" in the b-profile files. It is optional to the individual DAC to use the MTIME parameter.