Data integration attempts to improve the spatial coverage of observations
used in modeling studies by combining measurement records maintained by
independent laboratories into a cooperative globally-consistent data set.
The term "globally-consistent" implies that when extending and integrating
measurements records from independent programs, inconsistencies related
to maintenance and propagation of calibration scale, sampling, analysis,
and data processing and selection are minimal and do not introduce
significant uncertainties when interpreting model output. At the moment,
assessing consistency among measurements from independent programs relies
on results from round-robin exercises (e.g., WMO/IAEA sponsored experiments)
and comparisons with other sites and reference records. A major limitation
of the round-robin experiments is that they take 2-3 years to complete. By
the time the experiment is completed, the results give only a snapshot at
one point in time; we do not know from this experiment how
discrepancies may evolve in time.
More frequent and ongoing comparison experiments such as the flask-air
intercomparison between NOAA and CSIRO [Masarie et al., 2001] and the
CarboEurope Sausage Comparison [Levin et al., 2005] are critical to this effort.
It is not an easy task to assess the level of comparability between two independent
sets of observations due to the differences in scales, methodology and the inherent
complexity of making high-precision atmospheric trace gas measurements.
The WMO/IAEA carbon cycle atmospheric measurement community recommends target
levels of comparability required to address current carbon cycle scientific
issues. Table 1 summarizes their recommendations.
Table 1:Recommended inter-laboratory (network) comparability of components.
Component |
Inter-Laboratory comparability |
CO2 |
± 0.1 µmol mol-1 (± 0.05 µmol mol-1 in the southern hemisphere) |
δ13C-CO2 |
± 0.01 ‰ |
δ18O-CO2 |
± 0.05 ‰ |
Δ14C-CO2 |
± 1 ‰ |
O2/N2 |
± 1 per meg |
CH4 |
± 2 nmol mol-1 |
CO |
± 2 nmol mol-1 |
N2O |
± 0.1 nmol mol-1 |
H2 |
± 2 nmol mol-1 |
Source:13th WMO/IAEA Meeting of Experts on Carbone Dioxide Concentration and Related Tracers Measurement Techniques, Boulder, Colorado, USA, 19-22 September 2005. (WMO TD No. 1359).