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

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Global Attributes

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

Table 4 shows the possible 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]

ADCP Nortek Aquadopp ADCP MOORED
CT Sea-Bird SeaCAT TIME1 N/A
CT Sea-Bird MicroCAT' TIME1 N/A
CT BR-6999 TIME1 N/A
ABSS Aquatec Aquascat ABS ABS N/A

1For DATA_TYPE = TIME, no DATA_SUB_TYPE is required

The CMGP 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]

Attribute Description Example value
PROJECT Long name of research project (funding) 'USGS Coastal Marine Geology Program'
EXPERIMENT Identifier chosen for experiment 'BOSTON'
DESCRIPTION Specific site identifier 'B BUOY'
MOORING Numeric identifier of the mooring/instrument 7671 (use 4 digits)
DELTA_T Sample interval 600 (always seconds)
WATER_DEPTH Best version of water depth at site 60 (always meters)
VAR_FILL Indicator of bad or missing data 1.0e35
VAR_DESC Short list of variables in the file 'u:v:w:Werr:AGC:PGd:Tx:P'
DATA_CMNT Provides additional information 'NO Pressure logged'
COMPOSITE Number of pieces in a composite series 0 if not composite
FILL_FLAG Were fill values inserted? 0 if no, 1 if yes
DRIFTER Is the platform drifting? 0 if no, 1 if yes
POS_CONST Is the position consistent? 0 if it doesn't move, 1 if not consistent
DEPTH_CONST Does the depth change? 0 if consistent, 1 if not consistent
DATA_ORIGIN Organization collecting the data 'USGS WHSC Sed. Trans. Group'
COORD_SYSTEM How are coordinates mapped? 'GEOGRAPHICAL'
CREATION_DATE USGS WHCMSC usage is that this is the last MODIFIED date, not the initial creation date '31-Jan-2005 13:24:00'
WATER_MASS Description of water sampled normally unused

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-1.6, Climate and Forecast (version 1.6); hab, height above bottom; m, meter]

Attribute Description
Deployment_date date deployed
Recovery_date date recovered
latitude deployment latitude
longitude deployment longitude
magnetic_variation from NOAA Web site for position and time
start_time time of first record in file
stop_time time of last record in file
SciPi scientist responsible for the data
History1 all processing steps appended; most recent thing done is first in list
Conventions PMEL/EPIC or CF-1.6
serial_number Instrument or sensor serial number
inst_height Instrument or sensor hab (m)
inst_depth Instrument or sensor depth (m)
inst_heigh t_note note about accuracy
inst_depth_note note about accuracy

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.”

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