DOI: 10.6075/j0cchg47
title: CCHDO Hydrographic Data Archive, Version 2025-04-01. In CCHDO Hydrographic Data Archive

description: CCHDO contains hydrographic data collected from research vessels globally. Data are aggregated from science party submissions from programs such as GO-SHIP, WOCE, and CLIVAR aimed at reference-quality data. The data are assembled by cruise into several standard formats (e.g. WHP-Exchange, WOCE, and netCDF), as well as assessed for consistent parameter naming and flags, and known units of measurement. Data are not further quality controlled by CCHDO. 

The primary location of the CCHDO dataset is https://cchdo.ucsd.edu/. Snapshots of the CCHDO data and metadata are being deposited periodically for long-term preservation and access at the UC San Diego Library and are therefore also available through this collection. The most recent snapshot can be accessed at the top of the list of collection items.

Data Formats:
Data are available in CF/netCDF, WHP Exchange, COARDS netCDF, and WOCE text formats. CF/netCDF is a netCDF file following the Climate and Forecast metadata conventions available at https://cfconventions.org/, it is specifically using the incomplete multidimensional array representation of profiles defined in section 9.3.2. The WHP Exchange format is a CSV-like format described at https://exchange-format.readthedocs.io/. COARDS netCDF is an older netCDF metadata convention and uses one file per profile. The WOCE text formats, which are defined in Chapter 4 of WOCE Publication 90-1 uses separate formats for discrete and continuous data. Users of WOCE data must also download the Station Summaries, defined in Chapter 3 of WOCE Publication 90-1, for profile time and space information.

File Names:
All the file names in this snapshot have been regularized from what may be available on https://cchdo.ucsd.edu. All file names will start with the expedition identifier called an Expocode followed by an extension that identifies the type of data. Files and data from the same expedition will have the same Expocode. The following is a list of the extensions:

* Bottle
- CF/netCDF: _bottle.nc
- WHP Exchange: _hy1.csv
- COARDS netCDF _nc_hyd_.zip
- WOCE Text: hy.txt
* CTD
- CF/netCDF: _ctd.nc
- WHP Exchange: _ct1.zip
- COARDS netCDF _nc_ctd.zip
- WOCE Text: ct.zip
* Large Volume
- WOCE Text: lv.txt
* Cruise Reports:
- PDF: do.pdf
- text: do.txt
* Station Summaries
- WOCE Text: su.txt

Bottle Data:
The bottle data contains data from the analysis of water samples. While most of these data are from samples collected from Niskin bottle closures, it can also include any other discrete sample that was collected on an expedition. These data also typically include the readings from CTD sensors at the time of the bottle closure. For older data, it may also include readings from reversing thermometers. These data are available in all 4 formats.

CTD Data:
The CTD data contain in situ readings from instruments that were lowered into the ocean. Typically only the data read while the instrument package was being lowered is included. These data are usually grouped into 1 to 2 decibar pressure bins. Data from the major programs (WOCE, CLIVAR, GO-SHIP, GEOTRACES) will have had the sensors calibrated using data from the bottle samples. These data are available in all 4 formats.

Large Volume Sample Data:
Eleven expeditions from WOCE reported separate large volume samples. The large volume samples were done almost exclusively for radiocarbon measurements using a device called a Gerard Barrel. Improved analysis techniques eliminated the need for separate large volume sampling so radiocarbon measurements are integrated with the rest of the bottle data. These data are only available in the WOCE text format.

Cruise Reports:
The cruise reports are narratives of what happened on each expedition. These will include expedition goals, techniques utilized, preliminary data reports, and reports of issues. These reports are often very useful when investigating why some data may look unusual. These reports are available in PDF and text formats. The PDF formats will include figures and images not able to be included with the text versions.

Station Summaries:
Station summaries contain profile information including longitude, latitude, and times. It will contain one row per event and a single profile may have multiple events. The format is defined by chapter 3 of WOCE Publication 90-1. When using WOCE text formatted CTD, Bottle, or Large Volume sample data, these station summaries must also be downloaded.