Repeat Hydrography

Contact information for data centers (data submission)

Data policy for U.S. Global Repeat Hydrography Program, in support of US carbon cycle and CLIVAR programs

Lynne Talley, Nikki Gruber, Jim Swift with inputs from planning committee
December 20, 2001

The objective of the repeat hydrography program is to maintain decadal time-scale sampling of ocean transports and inventories of climatically significant parameters, such as carbon system components, nutrients, freshwater and heat. While autonomous sampling programs such as ARGO and the basin-scale volunteer observing ship programs can sample a portion of the climate-relevant fields, that is, parameters important for heat and freshwater in the upper part of the water column, they cannot at this time sample the entire water column nor can they sample important chemical tracer constituents. These semi-autonomous programs also cannot provide calibrated data; sensors presently in use are subject to drift and require occasional verification by in situ measurements.

The repeat hydrography program is ongoing sampling in support of improved understanding and modeling of climate and the carbon system, rather than characterization of the long-term mean regional, basin-scale and global circulation and basic property fields.

Thus the following data policy for hydrographic observations is adopted:

  • Observations will be made publicly available in preliminary form through a specified data assembly center as soon after collection as is practical ("early release"), with final calibrated data provided publicly when available. Collection is interpreted as the completion of the determination of the value of the particular parameter. Thus, for example, tritium/helium collection may not be complete for over a year after return to shore/laboratory. Timelines for each type of data are given in "Data submission" below.

  • All data collected as part of the repeat hydrography program will be submitted to a designated data management structure for quality control and dissemination for synthesis.

  • General U.S. national policy, applicable to all data collection programs, requires that post cruise inventory information (ROSCOP form) be completed within 60 days of the end of the cruise, usually by the Chief Scientist. Ultimately, all data must be archived with the National Oceanographic Data Center, following timelines set by the funding agencies.

This data policy achieves at least two objectives:

  1. It allows data to be incorporated in a variety of analyses, including data assimilation, as soon as possible after collection, and carried out by numerous investigators, consonant with data policies for more rapidly sampled ocean observation programs, such as ARGO, VOS and satellite observations programs, as well as atmospheric observation programs.
  2. Reduction in the lengthy delays in data availability that occurred during WOCE despite the stated two-year proprietary period.

While, historically, oceanographic data in the U.S. has been proprietary for some time period, typically two years, this paradigm is shifting. For example, the TAO and ARGO arrays both explicitly recognize the scientific and societal value of public and easy access to their data in "real-time". The "early release" policy for repeat hydrographic data recognizes that these data too are a publicly funded asset of significant scientific and societal importance.

It is recognized that well-qualified, experienced and highly-motivated investigators are necessary for success of the observation programs. Mechanisms will be provided for involvement of such investigators in acquisition of the data sets. Data analyses will be funded separately through competitive proposals. Those who collect the data will typically be in the forefront of those proposing analyses.

It is recognized that other nations may not initially subscribe to this type of data policy since their funding may be continuing under policies requiring much individual initiative. We urge that international data policies be adopted that adhere to the WOCE requirements at a minimum (two year release from time of analysis), and that the international data policies eventually converge with the U.S. policy. In unilateral recognition of the international importance of these globally distributed repeat hydrographic sections, and as an example to other nations, the U.S. "early release" data policy will allow access to U.S. repeat hydrographic data to all investigators.

For U.S. repeat hydrographic measurements collected on non-U.S. ships in order to complete the suite of Level 1 and 2 measurements, the data release requirements may differ. See "Sampling support for non-U.S. cruises" section below.

National and international oversight:

A U.S. Science Steering Committee (SSC) is required to oversee the program. The committee will advocate adequate and consistent coverage of all Level 1 and 2 observations. It will ensure smooth interactions with funding agencies and individual investigators, including those proposing Level 3 measurements. It will ensure that adequate support is provided for the necessary data assembly center structures.

The U.S. SSC will also interact with other national committees, international committees and structures carrying out large-scale repeat hydrographic programs.

Within the U.S. a consortium of scientists will lead each Level 1 and 2 observation type. Each consortium will consist of the principal investigators and data managers associated with that data type. The consortia should work to integrate all aspects of the program within the framework of the Carbon/CLIVAR national and international program requirements. Each repeat section will include a line coordinator. For U.S. lines, the fieldwork will be led by an experienced chief scientist, who may also be the line coordinator, and co-chief scientist. Guidelines for the proposed support for these investigators, including a scientific party of 2 to accompany them on the cruise, are given in the proposal.

The data management structures will serve the U.S. community. If international agreements to this end can be achieved, the data management structures could also serve the international contributions to the global repeat hydrography program.

Application of the data policy - timeline:

The "early release" data policy applies to all measurements in the core program for repeat hydrography, including both Levels 1 and 2 (see core measurements).

Daily during cruise:

  • Reduced temperature, salinity, depth data sets via GTS as TESAC messages.

  • Meteorological observations.

Within 5 weeks of the cruise, released to the relevant data management structure:

  • Preliminary CTD (pressure, temperature, salinity, oxygen if measured)

  • A merged bottle data file including preliminary discrete salinity, oxygen, nutrients (and carbon system components)

  • Preliminary CFC-11, CFC-12, CFC-113

  • Underway data, including continuous (1-minute) navigation, bathymetry, shipboard meteorological measurements, temperature, salinity, pCO2 (if measured).

  • Shipboard ADCP data

Within 6 months of the cruise, presuming the 5-week release of CTD and discrete salinity data:

  • Final salinity, oxygen, nutrients, CFC, CTD data

  • Final underway data

  • Final shipboard ADCP data

  • Final carbon system parameters (Total CO2 and Total Alkalinity required; pH, pCO2 if measured)

  • CDOM if measured

  • Lowered ADCP (if measured)

  • Any other Level 2 measurements

Within 6 months of shore-based analysis:

  • Tritium/helium

  • 14C and 13C

  • DON if measured

Within 2 years of analysis (required NSF data release schedule):

  • Any other (Level 3) observations. Those based on discrete bottle samples should be submitted to the hydrographic data management structure and merged with the other bottle data. (These include measurements such as NH4, low level nutrients, DMS and methyl halides, other trace metals, chlorophyll, TOP.)

  • Underway data should be submitted to the underway data management structure to be merged with the Level 1 and 2 underway data.

  • Other discrete sampling programs that are likely to be carried out on many of the cruises, such as transmissometry and optics, should be submitted to the relevant data management groups (examples are a JGOFS SMP project for global transmissometry, and the NASA DAC for optics).

Pre-cruise planning:

Each cruise will be planned by the Chief Scientist and principal investigators responsible for Level 1 and 2 measurements, taking into consideration any special requests by other principal investigators for Level 3 measurements. Priority for berths and ship laboratory space will be given to the observation programs in Levels 1 and 2. Reasonable requests for wiretime, laboratory space and berths will be accommodated for Level 3 observations. Any disputes will be negotiated with assistance from the Science Steering Committee (SSC).

The list of sampling programs and investigators will be submitted to the Science Steering Committee 9 months prior to the cruise, to allow the SSC to cover any missing observation types. The SSC and funding agencies will ensure that all Level 1 measurements are covered adequately for each cruise, and that as many of the Level 2 measurements as possible are also included.

The final sampling program, including exact cruise track, nominal station locations, parameters to be sampled, anticipated precision and accuracy of each measurements, and list of measurement groups or personnel should be filed with the SSC 3 months prior to the start of the cruise.

Data submission:

A subset of the temperature/salinity/depth and meteorological data should be submitted in near real-time during the cruise, through the GTS.

Data will be submitted following the cruise to the relevant data management structure within the required timelines specified above. Structures required for the repeat hydrography program (Level 1 and 2 data) should include centers for: CTD data, discrete bottle data, underway data, ADCP data and meteorological data. Most Level 3 data sets can be submitted to these centers; transmissometer and optical data should be submitted to management structures that will be designated prior to the beginning of the program. Some of these functions could or should be combined in a single office (e.g. hydrography, carbon and underway data could rationally be combined in one center), in order to increase efficiency and remove duplication of effort. One model might be that the present distributed and autonomous data centers function as units of a single (distributed) data center, with unified and streamlined procedures for efficient data assembly and quality control.


Sampling logs as required for the ROSCOP form submission, and at a minimum at the uniform standard for the WOCE hydrographic program's summary (.sum) files should be maintained. In addition, full information regarding sampling at each station should be logged, including depths, types of samples, any perceived problems with samples upon collection or initial analysis, personnel involved in analysis.

Documentation of sampling and analytical protocols should be submitted with the data sets. Documentation with the initial (early release) data submission should include a brief description of shipboard sampling procedures and precision and accuracy of observations. Documentation submitted with the final data set should also include detailed description of sample preparations, analytical procedures, equipment calibrations, data reduction techniques, computation algorithms, citations and anything else deemed necessary.

Data quality standards:

U.S. measurement standards should adhere to those set by WOCE and JGOFS for CTD, hydrographic properties and carbon system components.

Setting high standards for US data quality and delivery has international community-wide benefits, as in the WOCE Hydrographic Program. We encourage comparison studies of international scope.

There should be international distribution of a US methods handbook (prepared soon; required that US investigators use it) addressing reference materials, data quality goals, data flag protocols, (formats). A second version, prepared with international participation, may be pursued later; the US handbook is needed now.

To provide the opportunity for comparison with historical data, measurement techniques should be consistent with techniques used to collect the existing data unless there is significant scientific justification for change. When new techniques are adopted, methods for relating the new data to existing data should be developed. This requirement extends to regional comparisons as well.

As many measurements as possible should be made relative to a certified reference material standard. Such standards now exist for dissolved inorganic carbon, total alkalinity and CFCs. Standards for other Level 1/2 measurements are urgently needed, based on experience in WOCE and JGOS. These include standardization of oxygen analysis procedures (already developed) and development of nutrient standards.

U.S. support for observations on non-U.S. cruises:

A number of long repeat hydrographic sections in the overall plan are being carried out by other nations. Many of these do not include all Level 1 and 2 observations (see Table). U.S. groups have the capability to provide these measurements. The U.S. repeat hydrography plan therefore includes these observations. Data submission requirements as outlined above are waived for these groups, in recognition that the non-U.S. cruises will not be operating with the same submission deadlines and in recognition of the importance of collecting these observations for the long-term record of ocean change.

Data collected by U.S. investigators on non-U.S. cruises should still be submitted to the designated data management structures, at the time of public dissemination of the principal data sets or at two years, whichever is earlier. If the non-U.S. data sets have an embargo on publication that extends beyond 2 years, then the submitted U.S. data should remain proprietary, that is, without dissemination, until the non-U.S. release date.

The data management structures will make every effort to assemble the complete data sets, through contact with the non-U.S. principal investigators. An international agreement on the repeat hydrography program, data submission and designated data assembly centers should be sought.

Data management:

Data management is divided into two stages: (1) the principal investigators who are responsible for data collection, analysis, calibration, documentation, and submission to the data assembly centers and possibly NODC and (2) the data assembly centers that are responsible for data merging, online dissemination and documentation, a second stage of quality control (QC), and archiving at NODC.

At-sea data processing and documentation is most effective (but is expensive). At a minimum, there should be a data management person on board, who is responsible for merging data, assembling documentation, and other matters. The science team (consortium) will be helping the PI to process the data, but more by providing tools, advice, standards, etc., with the PI leading the processing. Thus the PIs doing the cruise must include data processing funds in their proposals to do the sea work. At a minimum, PI QC - applying flags as per a standard protocol - should be done, with a second level of QC as needed for some parameters, e.g. carbon system.

The bottle S/O2/nutrient/CFC data must be quality controlled and merged with preliminary processed CTD data shipboard quickly. These should be made available to the carbon PIs within 5 weeks of the cruise in order for the carbon data to be submitted within six months.

A single system of QC flag assignments and record keeping should be used for all bottle parameters.

The data management groups will be responsible for making the data accessible to the community via worldwide web servers, published or online data reports, CD-roms, etc.


Last Updated 11/29/2004
Lynne Talley