The spectral absorption coefficients of phytoplankton in oceanic waters were previously shown to vary with chlorophyll a concentration according to nonlinear relationships with a great deal of noise. We analyzed this biological noise on a data set of 596 simultaneous absorption and high‐pressure liquid chromatography (HPLC) pigment measurements acquired within the surface layer (first optical depth) from various regions of the world's oceans. We observed systematic deviations from the average relationships for some oceanic areas and also seasonally within given areas. Using the detailed HPLC measurements, the influences of pigment composition and package effect (the two main sources of variability in algal absorption for a given chlorophyll a concentration) were explicitly separated for each sample. It was found that while the pigment composition experiences large variations, even within a restricted chlorophyll range, it is often not (at least within the first optical depth) the dominant source of the biological noise. Instead, these deviations mostly result from variability in the pigment packaging effect (for a given chlorophyll a concentration) due to variations in algal community size structure. This conclusion is fully confirmed by an independent approach, which consists of estimating a “size index” of algal populations from the relative concentrations of taxonomic pigments.

The use of in situ measurements is essential in the validation and evaluation of the algorithms that provide coastal water quality data products from ocean colour satellite remote sensing. Over the past decade, various types of ocean colour algorithms have been developed to deal with the optical complexity of coastal waters. Yet there is a lack of a comprehensive intercomparison due to the availability of quality checked in situ databases. The CoastColour Round Robin (CCRR) project, funded by the European Space Agency (ESA), was designed to bring together three reference data sets using these to test algorithms and to assess their accuracy for retrieving water quality parameters. This paper provides a detailed description of these reference data sets, which include the Medium Resolution Imaging Spectrometer (MERIS) level 2 match-ups, in situ reflectance measurements, and synthetic data generated by a radiative transfer model (HydroLight). These data sets, representing mainly coastal waters, are available from doi:10.1594/PANGAEA.841950. The data sets mainly consist of 6484 marine reflectance (either multispectral or hyperspectral) associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: total suspended matter (TSM) and chlorophyll a (CHL) concentrations, and the absorption of coloured dissolved organic matter (CDOM). Inherent optical properties are also provided in the simulated data sets (5000 simulations) and from 3054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three data sets are compared. Match-up and in situ sites where deviations occur are identified. The distributions of the three reflectance data sets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.

Inshore estuarine, lagoonal, and reef waters of the Great Barrier Reef (Australia) were sampled between 2002 and 2005 during four dry and one wet tropical seasons. Relationships among three biogeochemical concentrations and five key water optical parameters measured at 129 stations were explored to optically characterize six predefined regions. A significant spatial and seasonal variability in some of the inherent optical properties and concentrations measured was found, reaching over two orders of magnitude in the estuaries. Total suspended solids concentrations ranged from 0.5 to ∼54 mg L⁻¹, TChl‐a ranged from 0.05 to ∼9 mg m⁻³, color dissolved organic matter (CDOM) ranged from 0.004 to 0.8 m⁻¹ at 440 nm, and the backscattering coefficient ranged from 0.001 to 1.18 m⁻¹ at 555 nm. Our data set was mainly composed of coastal stations (95%), leading to a poor correlation between the three concentrations (R² < 0.31). The range of variation in backscattering ratios, power law exponents, and the spectral slopes of CDOM and nonalgal particulate matter is comparable with findings from other coastal and open waters around the world. The empirical relationships between TChl‐a and a_ph(440) were found to differ from reference models, indicating differences in phytoplankton size structure and populations. High variability in backscattering ratios and associated power law exponents as well as particulate absorption ratios indicated different trends or relationships in particle size and composition between the different regions. Stations close to the reef matrix showed specific characteristics with concentrations typical of oceanic waters but CDOM spectral slopes similar to those of coastal environments.

To examine the source and magnitude of the variability of bio-optical properties in open ocean, we simultaneously measured inherent optical properties (IOPs) and biogeochemical quantities during late...