Assessment of Global Ocean Colour Products against In-situ Datasets
Ocean colour from satellite has given over the last two decades another dimension to ecosystem studies and marine biology, providing key information on the timing and spatial distribution of phytoplankton blooms, and the magnitude of primary production. Remote observations of ocean colour from space represent therefore a major tool directly related to the marine biogeochemical distributions and associated processes.
One of the goals of the European GMES Integrated Project MERSEA is to provide an accurate and consistent stream of ocean colour data, by exploiting the products made available in a number of individual missions launched by various space agencies. In this context, validation exercises, done via the direct comparison of satellite derived quantities with in situ measurements, represents a critical component in establishing the accuracy of the remotely-sensed data.
In this study we present a validation of Chlorophyll-a concentration derived from SeaWiFS and MODIS sensors, against in situ measurements retrieved from three different datasets (NODC, SeaBASS, JODC). The results of this comparison are well in line with previous analysis conducted on SeaWiFS, both from the point of view of the global statistics than for most of the regional results, and the uncertainties are lower than the value of 0.35 often considered as the objective for Chlorophyll-a distributions.
The SeaWiFS global average of RMS difference (for log-transformed values) shows an uncertainty of 0.29, while it is is slightly higher for MODIS (0.31), a difference likely partly due to a smaller statistical basis. The agreement is better for open ocean regions (RMSD reduced
to 0.26 and 0.27 for SeaWiFS and MODIS respectively) than for coastal areas.
An important objective of this work, that goes beyond the scope of the present report, was to develop the validation procedure and protocols for further analyses regularly reviewing validation results to take into account successive reprocessing and other sensors, as well as including additional in situ data sets.
CLERICI Marco;
MELIN Frederic;
HOEPFFNER Nicolas;
2008-05-13
OPOCE
JRC45007
1018-5593,
EUR 23357 EN,
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