Documentation of the U.S. Geological Survey Oceanographic Time-Series Measurement Database

This section describes typical usage of the generic global attribute fields in USGS/CMHRP netCDF files. The metadata included are a combination of attributes defined in the EPIC and CF conventions, with additional descriptors CMHRP investigators find useful. EPIC attributes are CAPITALIZED; the ones added by CMHRP are not, or may be Of_Mixed_Case.

For CF-compliant files, attribute and metadata usage follows CF conventions, and users should defer to the appropriate CF conventions document for guidance. The attributes listed on this page are a nonexhaustive collection, and other attributes may be included as processing routines evolve.

Table 4 shows the typical values of EPIC global attributes named INST_TYPE, DATA_TYPE, and DATA_SUB_TYPE that describe the sensor. These terms may be used by other software to determine how the data are treated, so consistency in terms is needed. Column 1 is the generic instrument name we use; columns 2 to 4 are the terms required by EPIC for the attribute names in the first row of each column. Other options may exist for some attributes; for instance, DATA_TYPE may be PROFILE for a CTD lowered from a ship, but because our CTD measurements are made at a single depth, by EPIC's rules, the DATA_TYPE must be TIME.

Table 4: Equatorial Pacific Information Collection (EPIC) attributes that depend on instrument type.
[ADCP, acoustic Doppler current profiler; RD Inst., Teledyne RD Instruments; PCADP, pulse-coherent acoustic Doppler profiler; ABS, acoustic backscatter sensor; N/A, not applicable]

¹For DATA_TYPE = TIME, no DATA_SUB_TYPE is required

The CMHRP also includes many instrument-specific identification and configuration details that may help users reconstruct how the data were collected and processed. For instance, ADCP data files typically have the following attributes (among others) that are added:

• transform : earth
• orientation : up
• frequency : 300
• pings_per_ensemble : 60

EPIC conventions also specify the attributes shown in table 5 that are present in all data files. These specify who did the work, why, how often, and other details of what is expected in the data.

Table 5:Equatorial Pacific Information Collection (EPIC) attribute names found in all data types.
[USGS, U.S. Geological Survey; WHCMSC, Woods Hole Coastal and Marine Science Center; WHSC Sed. Trans. Group, Woods Hole Coastal and Marine Science Center Sediment Transport Group]

The attributes listed in table 6 are not required by EPIC but have been included in the more recently processed files to more accurately document the deployment details and processing steps. The Conventions attribute tells other programs what vocabulary was used in attribute and variable naming. It is similar to indicating "this page is written in Danish"—it helps software interpret the information correctly.

Table 6: Additional attributes typically employed.
[NOAA, National Oceanic and Atmospheric Administration; PMEL, Pacific Marine Environmental Laboratory; EPIC, Equatorial Pacific Information Collection; CF, Climate and Forecast (version 1.6 or later); hab, height above bottom; m, meter]

¹The history attribute is the best place to look for provenance, including which programs were run, the processing sequence, and if data were truncated. There may also be a “note” or “comment” attribute added to document an event, such as “tripod tipped over in a storm on Feb. 2, 1998.”