NOAA Logo National Centers for Environmental Information

formerly the National Oceanographic Data Center (NODC)...  more on NCEI

NOAA Satellite and Information Service

You are here:HomeGTSPP › Documents

NetCDF Format Description

This section describes the netCDF conventions proposed by the NODC for use with the Global Temperature-Salinity Profile Program (GTSPP) data. The NetCDF conventions, also known as the GTSPP netCDF conventions, fully conform to the conventions used by the Cooperative Ocean/Atmosphere Research Data Service (COARDS) and World Ocean Circulation Experiment (WOCE). The COARDS/WOCE netCDF conventions have been widely recognized by numerous software plotting and analysis packages, for examples, ncBrowse and Ocean Data View, to provide more automatic processing, plotting, and analysis capabilities. It is very important that the GTSPP netCDF format files has the same capability as the WOCE data files have.

NetCDF Format Description

All GTSPP data is located by longitude, latitude, depth and time and is represented by three spatial axes (longitude, latitude, and depth) and one temporal (time) axis. Other information is not included as an axis, it must be included elsewhere within the data file, if the file is to be self-describing.

====
AXES
====
Axes
GTSPP data axis conventions are described here. Geographic axes in a GTSPP netCDF file are, at present, described by a numeric variable code included as an attribute in the data file. There is a disk file named "epic.key" which contains all EPIC variable codes with other related information. The numeric variable code is a unique identifier for the variable or axis, and is described more fully in the section below on "VARIABLES". The use of the numeric variable code to define the axis is necessary for EPS libary V2.1 and earlier, and for PPLUS V1.2c and earlier. In future releases of both the EPS libarary and PPLUS, the use of an axis variable code may be replaced by the use of units from UDUNITS, and may no longer be required.

Longitude axis
--------------

Many longitude representations are possible, however, for compatibility with the WOCE netCDF conventions, use East longitude convention, described in detail below, defines the numeric representation of the longitude axis in the netCDF file, with positive values for east longitudes. The recommended East longitude convention is described in the following paragraphs.

We recommend that users represent the longitude axis with the East longitude convention. This means that eastern longitudes are positive numbers, for example, 170E is +170.0. The units of the axis are degree_east.

Latitude axis
-------------
The recommended latitude convention is for north latitudes to be represented by positive numbers (e.g., 10N is +10.0), and south latitudes by negative numbers (e.g., 10S is -10.0). The units of the axis are degree_north.

Depth axis
----------
The depth axis should be given with the oceanographic convention of depth as a positive number, increasing downwards from the surface of the water towards the bottom of the ocean. The units of the axis should be dbar (pressure axis) or meters (depth axis).

Time axis
---------

The representation of the time axis within the data file can be of several types, including the WOCE standard, the double real numeric array, which will be "days since 1900-01-01 00:00:00 UTC", and some other time representations, which are supported for compatibility with the units used in the Argo netCDF convention - "days since 1950-01-01 00:00:00 UTC".

The standard units of the time axis EPIC system library routines return the time axis from a data file to the calling routine in the form of a two-integer array, in which the first integer is the "True Julian Day Number" with units of days, and the second integer is the number of milliseconds since 0000 GMT of the True Julian Day. The True Julian Day (eg, May 23, 1968 is 2,400,000), used by astronomers, should not be confused with the "year-day"
(eg, Feb 2 is year-day 33). The "year-day" is frequently called julian day (incorrectly) by oceanographers and meteorologists. Our double-dimensioned integer time word (word1=True Julian Day, word2=milliseconds since 0000 GMT of the True Julian Day) allows millisecond accuracy for time periods extending over centuries. There is a complete set of EPS routines for manipulation, calculation, and character string representation of this standard representation of time.

Time axes can be written or read in either real or integer format.

==========
VARIABLES
==========

Global Attribute Section
Attribute Name Attribute Value
Conventions CF-1.6
title Global Temperature and Salinity Profile Programme (GTSPP) Data
summary The data source is the GTSPP Continuously Managed Data Base
keywords temperature, salinity, sea_water_temperature, sea_water_salinity
keywords_vocabulary NODC Data Types, CF Standard Names
references http://www.nodc.noaa.gov/gtspp/
institution U.S. National Oceanographic Data Center
project Joint IODE/JCOMM Global Temperature-Salinity Profile Programme
id gtspp_dbid_13978451
naming_authority gov.noaa.nodc
standard_name_vocabulary CF-1.6
Metadata_Convention Unidata Dataset Discovery v1.0
publisher_name US DOC; NESDIS; NATIONAL OCEANOGRAPHIC DATA CENTER - IN295
publisher_url http://www.nodc.noaa.gov/gtspp/
publisher_email nodc.gtspp@noaa.gov
date_created 2012-05-01
date_modified 2012-05-01
date_issued 2012-05-01
history 2012-05-01T18:34:36Z writeGTSPPnc40.f90 Version 1.7
acknowledgment These data were acquired from the US NOAA National Oceanographic Data Center (NODC) on [DATE] from http://www.nodc.noaa.gov/gtspp/.
license These data are openly available to the public. Please acknowledge the use of these data with the text given in the acknowledgment attribute.
comment GTSPP4.0 adapted the ACDD, COARDS, and CF-1.6 conventions including CF discrete sampling geometry for profiles.
featureType profile
cdm_data_type profile
geospatial_lat_min 30.43700
geospatial_lat_max 30.43700
geospatial_lon_min -88.01200
geospatial_lon_max -88.01200
geospatial_vertical_min 2.000000
geospatial_vertical_max 3.000000
geospatial_lat_units degrees_north
geospatial_lat_resolution point
geospatial_lon_units degrees_east
geospatial_lon_resolution point
geospatial_vertical_units meters
geospatial_vertical_resolution point
geospatial_vertical_positive down
time_coverage_start 2012-04-27T10:30Z
time_coverage_end 2012-04-27T10:30Z
time_coverage_duration point
time_coverage_resolution point
gtspp_ConventionVersion GTSPP4.0
gtspp_program writeGTSPPnc40.f90
gtspp_programVersion 1.7
gtspp_handbook_version GTSPP Data User's Manual 1.0
LEXICON NODC_GTSPP

Variable Metadata Section
Variable ID Number Variable Name Variable Type Number of Attributes Number of Dimensions
1 format_version char 2 1
2 gtspp_station_id int 3 0
3 crc char 3 1
4 best_quality_flag int 4 0
5 time double 5 1
6 time_quality_flag int 5 0
7 latitude float 5 1
8 longitude float 5 1
9 position_quality_flag int 5 0
10 qc_version char 2 1
11 gtspp_temperature_instrument_code char 5 1
12 gtspp_platform_code char 2 1
13 data_type char 3 1
14 one_deg_sq int 1 0
15 cruise_id char 5 1
16 source_id char 3 1
17 stream_ident char 3 1
18 uflag char 3 1
19 no_prof short 2 0
20 prof_type char 1 2
21 z float 13 1
22 z_variable_quality_flag int 5 1
23 temperature float 13 4
24 temperature_quality_flag int 6 1
25 salinity float 14 4
26 salinity_quality_flag int 6 1
27 no_surf short 1 0
28 surfacecodes_pcode char 3 2
29 surfacecodes_cparm char 2 2
30 no_hist short 1 0
31 hist_identcode char 1 2
32 hist_prccode char 3 2
33 hist_version char 2 2
34 hist_prcdate char 2 2
35 hist_actcode char 3 2
36 hist_actparm char 3 2
37 hist_auxid char 2 2
38 hist_ovalue char 2 2
39 crs int 6 0

Data Metadata Section
Variable Name Variable Type Attribute Name Attribute Value
format_version char  
    long_name File Format Version
    comment Version number of the GTSPP NetCDF format
gtspp_station_id int  
    long_name Station ID Number
    cf_role profile_id
    comment Identification number of the station in the GTSPP Continuously Managed Database
crc char  
    long_name Cyclic Redundancy Check (CRC)
    _FillValue X
    comment A CRC algorithm used to generate an unique data tag of this record
best_quality_flag int  
    long_name Best Quality Flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
time double  
    long_name time
    standard_name time
    units days since 1900-01-01 00:00:00
    axis T
    ancillary_variables time_quality_flag
time_quality_flag int  
    long_name Date-Time Quality Flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    _FillValue -9
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
latitude float  
    long_name latitude
    standard_name latitude
    units degrees_north
    axis Y
    ancillary_variables position_quality_flag
longitude float  
    long_name longitude
    standard_name longitude
    units degrees_east
    axis X
    ancillary_variables position_quality_flag
position_quality_flag int  
    long_name Position Quality Flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    _FillValue -9
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
qc_version char  
    long_name QC Program Version No.
    comment Version of the QC program used.
gtspp_temperature_instrument_code char  
    long_name GTSPP Temperature Instrument Code
    instrument_type CTD
    recorder_type Unknown
    comment GTSPP code for temperature instrument type (first three digits, WMO-1770), with fall rate equation coefficients for XBT (last two digits, WMO-4770).
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/wmocode.html
gtspp_platform_code char  
    long_name GTSPP Platform Code
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/calllist.html
data_type char  
    long_name Data Type
    comment TESAC message
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/gtsppcode.html#TYPE
one_deg_sq int  
    long_name GTSPP geographic one degree square
cruise_id char  
    long_name Cruise_ID
    callsign MBLA1
    year 12
    _FillValue X
    comment Radio callsign + year for real time data
source_id char  
    long_name Source ID
    _FillValue X
    comment Global Telecommunication System (GTS) node which placed message on the GTS
stream_ident char  
    long_name Stream Identification
    _FillValue X
    comment Source and type of data. Bytes 1-2 show the data source center. Bytes 3-4 show data type
uflag char  
    long_name Update Flag
    _FillValue X
    comment Record update action
no_prof short  
    long_name Number of Profiles
    comment Number of Parameter profiles in station
prof_type char  
    long_name Profile Type
z float  
    long_name Depths of the observations
    standard_name depth
    units meters
    deepest_depth 3.000000
    positive down
    axis Z
    ancillary_variables z_variable_quality_flag
    data_min 2.000000
    data_max 3.000000
    C_format %6.2f
    FORTRAN_format F6.2
    epic_code 3
    _FillValue 99999.00
z_variable_quality_flag int  
    long_name Depth/Press Quality Flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    _FillValue -9
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
temperature float  
    long_name sea water temperature
    standard_name sea_water_temperature
    units degrees_C
    coordinates time latitude longitude z
    grid_mapping crs
    cell_methods time:point lon:point lat:point z:point
    ancillary_variables temperature_quality_flag
    data_min 19.80000
    data_max 19.80000
    C_format %9.4f
    FORTRAN_format F9.4
    epic_code 28
    _FillValue 99999.00
temperature_quality_flag int  
    long_name Global quality flag of sea water temperature profile
    standard_name sea_water_temperature status_flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    _FillValue -9
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
salinity float  
    long_name Practical Salinity
    standard_name sea_water_salinity
    salinity_scale psu
    units psu
    coordinates time latitude longitude z
    grid_mapping crs
    cell_methods time:point lon:point lat:point z:point
    ancillary_variables salinity_quality_flag
    data_min 2.900000
    data_max 2.900000
    C_format %9.4f
    FORTRAN_format F9.4
    epic_code 41
    _FillValue 99999.00
salinity_quality_flag int  
    long_name Global quality flag of sea water salinity profile
    standard_name sea_water_salinity_qc_flag
    flag_values 0 1 2 3 4 5 6 7 8 9
    flag_meanings no_quality_control_performed good_value probably_good probably_bad bad_value modified_value reserved reserved reserved missing_value
    _FillValue -9
    references http://www.nodc.noaa.gov/GTSPP/document/qcmans/qcflags.htm
no_surf short  
    long_name Number of Surface Codes Groups
surfacecodes_pcode char  
    long_name Surface Parameter Code
    comment Consult the GTSPP and WMO Code Tables to interpret what variable this is
    references http://www.nodc.noaa.gov/GTSPP/document/codetbls/gtsppcode.html
surfacecodes_cparm char  
    long_name Surface Parameter Value
    comment Consult the GTSPP and WMO Code Tables to interpret what variable this is
no_hist short  
    long_name Number of History groups
hist_identcode char  
    long_name History Identification Code
hist_prccode char  
    long_name History Processing Code
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/gtsppcode.html#PRC
    comment Identifies the procedure through which the data passed.
hist_version char  
    long_name History Processing Version
    comment Identifies the version of the software through which the data passed.
hist_prcdate char  
    long_name History Processing Date
    comment Records the date as YYYYMMDD that this history record was created.
hist_actcode char  
    long_name History Action Code
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/gtsppcode.html#PC_HIST
    comment Identifies the action taken against the data by the software.
hist_actparm char  
    long_name History Action Parm
    references http://www.nodc.noaa.gov/gtspp/document/codetbls/gtsppcode.html#PC_PARM
    comment Identifies the measured variable affected by the action.
hist_auxid char  
    long_name History Auxilary Identification
    comment Normally this is the depth at which the value of a variable was acted upon by the software.
hist_ovalue char  
    long_name History Original Value
    comment The original value before being acted upon by software.
crs int  
    long_name Coordinate Reference System
    grid_mapping_name latitude_longitude
    epsg_code EPSG:4326
    longitude_of_prime_meridian 0.0f
    semi_major_axis 6378137.0
    inverse_flattening 298.257223563