Data are made available to the Indian Ocean Centre via the global UOT archives (NOAA's National Oceanographic Data Centre [NODC] in the U.S., the Marine Environmental Data Service [MEDS] in Canada, and the Global Thermal Salinity Data Centre in France). This is achieved under the Global Temperature Salinity Profile Project (GTSPP), which is a joint project of the Integrated Global Ocean Services System (IGOSS) and the Intergovernmental Oceanographic Data Exchange (IODE).

The WOCE UOT/DACs also operate as Regional Science Centres within GTSPP.

Data are classified into two data streams:  Real-Time and Delayed Mode.

• Real Time data are data transmitted (usually via satellite) in real-time by the reporting platforms; they are usually of lower resolution and quality.
• Delayed Mode data are the full-resolution data collected from the platform after the event; they are usually of higher quality and accordingly more useful in scientific research.

The Delayed Mode data, when submitted by the data collection agencies, replaces the Real Time data in the global archives.
 
Both data streams undergo preliminary QC by the data collection agencies and national/international data centres before submission to the regional UOT/DACs. After sufficient  high resolution data have replaced Real Time data(ideally 75-85%), they are forwarded to the UOT/DACs for QC. Unfortunately, replacement can sometimes take several years after actual data collection, and sometimes the Delayed Mode data are never submitted.

After scientific QC at the UOT/DACs, the data is returned to the main global archive (NODC) for distribution to the community (including via the WOCE CD ROM Data Sets).

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SCIENTIFIC QUALITY CONTROL

Scientific quality control is the process of combining statistical analyses of the data (in this case, subsurface temperature profiles) with knowledge of historical means (climatology) and of the relevant environment (regional oceanography) to make a scientifically based decision about the validity of each data point. Knowledge of the recording instrument's performance and characteristics is also used. Quality control is a vital prerequisite to scientific analysis.

Unless data centres have the appropriate in-house scientific expertise and are using the data for scientific applications, this type of QC (value-added) cannot be accomplished by the data centres alone. Regional UOT/DACs were therefore established to ensure regional scientific expertise was included in the QC process, while also helping to distribute the large QC load for UOT data.

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"QUEST" QUALITY CONTROL AND ANALYSIS SYSTEM

CMR and BMRC have developed a comprehensive software system for the scientific quality control of subsurface ocean temperature data. The system is called QUEST (which stands for Quality Evaluation of Subsurface Temperatures; in Bailey et al., 1998). QUEST combines the subsurface ocean temperature statistical analysis scheme developed by BMRC in conjunction with CSIRO (see Blomley et al. 1989; Smith 1991; Meyers et al. 1990; Phillips et al. 1990; Smith et al. 1991) with the quality control procedures of CSIRO (see Bailey et al. 1994 - often referred to as the "CSIRO Cookbook").

QUEST enables individual temperature profiles to be compared to:

• Climatology (Levitus);
• an objective (statistical) analysis of all the available data; and
• other profiles in the immediate area (present and historical).

This facilitates the identification of real features of a given region, and helps distinguish between such features and erroneous data. All scientific decisions are recorded/flagged with the data according to the CSIRO Cookbook and WOCE guidelines. A summary of the QC results is given in Table 1.

Generally the data received from the global data archives are of a reasonable quality (82.4%). However, a significant number of data in the archives have subtle instrument errors (17.6%), which are hard to detect by untrained observers and QC operators. These subtle errors (and sometimes large errors that have escaped automated QC checks at the data centres) are capable of seriously affecting many scientific analyses, particularly those looking for climate signals in the data sets.

Analysed temperature fields are produced by the objective analysis scheme of Blomley et al. (1989).  The Bureau of Meteorology uses this system operationally on real-time data:

link to BMRC Ocean Analyses 

These fields are also used in the final quality control of the data (e.g. bulls-eye analysis). Given the relatively sparse data coverage of the Indian Ocean compared to other oceans, separate statistics are also generated along the most frequently repeated XBT lines operated under WOCE.

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SUMMARY

• A high-quality, consistent UOT data set has been assembled for WOCE.
• The 0.2-0.50^oC accuracies provided by the extensive profile-by-profile examination during the scientific QC process are crucial for detecting interannual and interdecadal signals, as well as for developing Climatologies.
•  The analysed UOT data set can be used to establish the extent to which other WOCE measurements (such as the hydrographic sections) are representative of the ocean state.
• Powerful tools and procedures, developed for the scientific QC of UOT data, are now implemented at operational agencies and data centres through a transfer of expertise and technology program.

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REFERENCES

Bailey, R., A. Gronell, and N. R. Smith, 1998: Scientific Quality Control at the WOCE Indian Ocean Upper Ocean Thermal Data Assembly Centre. CSIRO Marine Laboratories Report. (in preparation).

Bailey, R., A. Gronell, H. Phillips, G. Meyers and E. Tanner, 1994: CSIRO Cookbook for Quality Control of Expendable Bathythermograph (XBT) Data. CSIRO Marine Laboratories Report, 221, 75 pp.

Blomley, J. E., N. R. Smith and G. Meyers, 1989: An Oceanic Subsurface Thermal Analysis Scheme.  BMRC Research Report, 18. 65pp.

Meyers, G., H. Phillips, N. Smith and J. Sprintall, 1991: Space and time scales for optimal interpolation of temperature - Tropical Pacific Ocean. Prog. Oceanog., 28, 189-218.

Phillips, H., R. Bailey, and G. Meyers, 1990: Design of an Ocean Temperature Observing Network in the Seas North of Australia. Part II; Tropical Indian Ocean: Statistics. CSIRO Marine Laboratories Report, 211, 58 pp.

Smith, N. R., 1991: Objective Quality Control and Performance Diagnostics of an Oceanic Subsurface Thermal Analysis Scheme. J. Geophysical Res., 96, 3279-3287.

Smith, N. R., J. E. Blomley and G. Meyers, 1991: A univariate statistical interpolation scheme for subsurface thermal analyses in the tropical oceans. Prog. Oceanog., 28, 219-256.

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ACKNOWLEDGMENTS

Funding was provided by the CSIRO Marine Research (CMR), Bureau of Meteorology Research Centre (BMRC), and the Department of the Environment, Sports and Territories (DEST). This work would not have been possible without support from the CSIRO Climate Change Research Program (CCRP). Neil Smith (BoM) and Helen Phillips (CSIRO) contributed to the software and QC procedure development respectively. Edwina Tanner and Andrew Walsh from the AODC participated in the QC training program.

We also gratefully acknowledge all the agencies, individuals and programs who have collected and contributed data to NODC, the Marine Environmental Data Centre and the Global Subsurface Data Centre.

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