Data Checks and Processing Performed by CDIAC
An important part of the NDP process at the Carbon Dioxide Information Analysis Center (CDIAC) involves the quality assurance (QA) of data before distribution. Data received at CDIAC are rarely in a condition that would permit immediate distribution, regardless of the source. To guarantee data of the highest possible quality, CDIAC conducts extensive QA reviews that involve examining the data for completeness, reasonableness, and accuracy. Although they have common objectives, these reviews are tailored to each data set, often requiring extensive programming efforts. In short, the QA process is a critical component in the value-added concept of supplying accurate, usable data for researchers.
The following summarizes the data-processing and QA checks performed by CDIAC on the data obtained during the R/V Meteor Expedition 11/5 in the South Atlantic Ocean and Northern Weddell Sea areas.
- These data were provided to CDIAC in three files: CO2 measurements, along with downgraded hydrographic and chemical data, provided by Taro Takahashi and David Chipman from Lamont-Doherty Earth Observatory; hydrographic and chemical measurements, and station information files provided by the WOCE Hydrographic Program Office (WHPO) after quality evaluation; FORTRAN 77 retrieval code written and used to merge and reformat the first two data files.
- All data were plotted by using a PLOTNEST.C program written by Stewart C. Sutherland (LDEO) to check for obvious outliers. The program plots a series of nested profiles, using the station number as an offset; the first station is defined at the beginning, and subsequent stations are offset by a fixed interval (Fig. 4 and Fig. 5). Some outliers were identified and removed after consultation with the principal investigators.
- Property-property plots for all parameters were generated (Fig. 6), carefully examined, and compared with plots from previous expeditions in the South Atlantic Ocean to identify "noisy" data and possible systematic, methodological errors.
- All variables were checked for values exceeding physical limits, such as sampling depth values that are greater than the given bottom depths.
- Station locations (latitudes and longitudes) and sampling times were examined for consistency with maps and with cruise information supplied by Chipman et al. (1992).
- The designation for missing values, given as -9.0 in the original files, was changed to -999.9.