Improving the consistency of ocean color data: A step toward climate data records

[1] Two ocean color missions, SeaWiFS and MODIS, overlap in time and are processed with consistent methods. Global annual median chlorophyll from SeaWiFS and MODIS differ by 12.2%. These discrepancies exceed the maximum observed interannual variability globally and in every major oceanographic basin. Estimates of trends are affected as well. For 1998–2007 the SeaWiFS global trend is −2.6% (not statistically significant). Substitution of MODIS for SeaWiFS in 2003–2007 produces a −18% significant trend. A new approach that incorporates in situ data improves the consistency of the two sensor data sets. The global difference is −0.6% and the 10-year trend of SeaWiFS and MODIS agrees with standalone SeaWiFS (−3.3%, not significant). In oceanographic basins where sampling biases are small the differences are less than the maximum observed interannual variability. The approach improves the consistency of multiple successive ocean color missions and represents a step toward scientifically reliable Climate Data Records.