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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]
| Generic name |
INST_TYPE |
DATA_TYPE |
DATA_SUB_TYPE |
| ADCP |
RD Inst. ADCP |
ADCP |
MOORED |
| ADCP |
Nortek Aquadopp |
ADCP |
MOORED |
| ADCP |
RD Inst. ADCP |
ADCP |
MOORED |
| waves |
RD Inst. ADCP |
WAVESPEC |
N/A |
| CT |
Sea-Bird SeaCAT |
TIME1 |
N/A |
| CT |
Sea-Bird MicroCAT' |
TIME1 |
N/A |
| CT |
BR-6999 |
TIME1 |
N/A |
| ADV |
SonTek ADV |
TIME1 |
N/A |
| PCADP |
SonTek PCADP |
ADCP |
MOORED |
| 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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