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

Each variable in the file has its own attributes to describe and quantify the contents. The descriptors in the left column of table 7 are found in most variables; the column on the right contains sample values. If the parameter has more than one dimension, the minimum and maximum may be vector quantities instead of scalars. The minimum and maximum of the data are of the same units as the data—in the example in table 7, because the transducer temperature is “degrees C,” the maximum and minimum are as well. The sensor depth (water depth minus sensor height) is always meters. _FillValue is the number that represents erroneous or missing data in a time series. Sometimes the software may display _FillValue as 1.00000004091848e+035, but it is truly 1.0e+35. The valid_range attribute, if present, specifies the potential range of acceptable data.

Table 7: Attributes associated with each variable.

There may also be a “note” or “comment” added to document a sensor failure, such as “optical path obscured on Jan. 10, 2005; subsequent data replaced with fill value.”

Variable Names

Variable names in our files are formed from the EPIC key (ftp://ftp.epic.noaa.gov/epic/epic.key) by combining the abbreviation code and the number. The EPIC key lists code 1 as a pressure, abbreviated as “P,” in decibars, so the variable name that contains pressure data (in decibars) is “P_1.” Similarly, ocean temperature data has the abbreviation T for temperature and EPIC code 28 indicates it is from sea water of ITS–1990 standard, so the variable name is “T_28.” In the CF version of a file, the T_28 variable would have a “standard_name” attribute of “seawater_temperature” from the CF vocabulary, but is otherwise the same. When more than one sensor of a type is logged by the same instrument, a digit is added so the name becomes “Sed1_981” or “Sed2_981” for sediment concentration data. The most often used variable names are listed in table 8. When variable names are not present in the EPIC key, the CF standard name or another appropriate name is used.

Table 8 provides a subset of data variable names, the equivalent CF standard_name, and units for variables often found in the database, by type of measurement. Each file will contain only the variables appropriate to the kind of data the instrument collected. Alternate names for variables used in the older, pre-EPIC files are also listed.

Table 8: Data variable names, by type of data.
[cm/s, centimeter per second; m, meter; dbar, decibar; Pa, pascal; mbar, millibar; °C, degree Celsius; ITS–1990, International Temperature Scale of 1990; ADCP, acoustic Doppler current profiler; S/m, siemens per meter; PSU, practical salinity unit; microEinstein/m2/s, microEinstein per square meter per second; kg/m3, kilogram per cubic meter; %, percent; m/s, meter per second; NTU, nephelometric turbidity unit; W/m2, watt per square meter; --, not applicable]

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