Temporal Variability of Ocean Colour Derived Products in the European Seas

The ten-year record of ocean colour data provided by the SeaWiFS mission is an important asset for monitoring and research activities conducted on the optically-complex European seas. This study mainly makes use of the SeaWiFS data set of normalized water leaving radiances LWN to study the major characteristics of temporal variability associated with optical properties across the entire European domain. Specifically, the time series of LWN, band ratios, diffuse attenuation coefficient Kd(490) and concentration of chlorophyll a Chla are decomposed into terms representing a fixed seasonal cycle, irregular variations and trends, and the contribution of these components to the total variance is described for the various basins. The diversity of the European waters is fully reflected by the range of results varying with regions and wavelengths. Generally, the Mediterranean and Baltic seas appear as two end-members with, respectively, high and low contributions of the seasonal component to the total variance. The existence of linear trends affecting the satellite products is also explored for each basin. The interpretation of the trends observed for LWN and band ratios is not straightforward, but it circumvents the limitations resulting from the levels of uncertainty, very variable in space and often high, that characterize derived products such as Chla in European waters. Results for Kd(490) and Chla are also analyzed. Statistically significant, and in some cases large, trends are detected in the Atlantic Ocean west of the European western shelf, the central North Sea, the English Channel, the Black Sea, the northern Adriatic, and various regions of the Mediterranean Sea and the northern Baltic Sea, revealing changes in the concentrations of optically significant constituents in these regions.JRC.H.3-Global environement monitorin

Aerosol Direct Radiative Effect in the Po Valley Region Derived from AERONET Measurements

The aerosol direct radiative effect (ADRE) affecting the Po Valley and the adjacent North Adriatic Sea is studied using 10-year series of measurements collected at two AERONET sites located in the western part of the Valley (Ispra), and on a platform (AAOT) offshore Venice. This region is characterized by a high, mostly continental, aerosol load with comparable average aerosol optical thickness (AOT) at both locations (0.21 at 500 nm) and more absorbing aerosols at Ispra. A dynamic aerosol model accounting for the changes in scattering phase function with AOT is used for radiative transfer calculations, together with boundary conditions representative of terrestrial and marine surfaces. A sensitivity analysis allows the construction of an error budget for the daily ADRE estimates, found to be of the order of 20% and mostly due to uncertainties on aerosol single scattering albedo and AOT. The daily radiative efficiencies, normalized by AOT at 500 nm, increase from December to June, from -17 to -24 W m-2 AOT-1 at top-of-atmosphere (TOA) and -33 to -72 W m-2 AOT-1 at surface for the Po Valley, and from -15 to -32 (TOA) and -35 to -65 W W m-2 AOT-1 (surface) for the AAOT site. The average of log-transformed ADRE for TOA, surface and atmosphere are -5.2, -12.2 and +6.8 W m-2 for the Po Valley case, and -6.5, -13.0 and +6.5 W m-2 for the AAOT site but these values can be much higher for individual days. Concurrent clear-sky days give indications on the regional atmospheric heating spatial gradients. Differences between the atmospheric ADRE at the two locations average 6.3 W m-2 with a gradient positive towards the inner valley in 65% of the cases. This study confirms the importance of duly considering the radiative impact of aerosols on the regional climate.JRC.H.3-Global environement monitorin

Multi-Year Analysis of Standard Ocean Colour Products for the European Seas

A 10-year time series of ocean colour products has been assembled for the European Seas from the SeaWiFS and MODIS full resolution satellite imagery. The JRC ocean colour archive is first briefly described. Then the study focuses on the analysis of the spatial and temporal variability of standard products such as the chlorophyll a pigment concentration and the diffuse attenuation coefficient. The European seas are partitioned into a set of specific regions for which average time series are derived and analysed in terms of seasonal and inter-annual variability. Finally, a statistical analysis yields a decomposition of the series into seasonal, irregular and linear trend components, thus providing a classification of the European waters on the basis of their temporal variations.JRC.H.3-Global environement monitorin

Selected UV Photochemical and Photobiological Impacts on Marine Ecosystems: General Characteristics and Sensitivity Analyses

In the recent years, numerous efforts have been performed in order to characterize the impacts of UVR on marine photobiology and photochemistry. The quantification of these UV-dependent processes through modelling approaches requires (i) an accurate description of UV underwater light field (ii) an adapted parameterization of the response of marine water compounds and/or organisms to spatio-temporal changes in solar radiations. The spatial and temporal variability of the absorption coefficient of the colored detrital material, which is a key element for studying undersea UV climate, has been characterized in the two basins selected for this study (the Mediterranean Sea and the Norwegian Seas) using the SeaWiFS products archive recently achieved for the period 1998-2006. Moreover, the various models currently available for the description of selected optical (CDOM photobleaching), photochemical (CO and DIC production) and photobiological (primary production inhibition) effects of UVR on marine waters have been described. Further, the general characteristics of these UV-dependent processes have been presented focusing, in particularly, on their variability along the daily, vertical and spectral dimensions. Several sensitivity analyses have been performed in order to define the relative importance of the various inputs of the spectral and depth resolved model on the final estimations. Finally, some of the straightforward models recently proposed in order to estimate some of the UV impacts at large temporal and or spatial scales have been tested and their limits of application have been discussed.JRC.H.3-Global environement monitorin

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.JRC.H.3-Global environement monitorin

System Vicarious Calibration for Copernicus Ocean Colour Missions: Updated Requirements and Recommendations for a European Site

The Copernicus Program has been established through the Regulation EU No377/2014 with the objective to ensure long-term and sustained provision of accurate and reliable data on environment and security through dedicated services. Among these, the Copernicus Marine Environment Monitoring Service and the marine component of the Climate Change Service, both rely on satellite ocean colour observations to deliver data on water quality and climate relevant quantities such as chlorophyll-a concentration used as a proxy for phytoplankton biomass. Satellite ocean colour missions require in situ highly accurate radiometric measurements for the indirect calibration (so called System Vicarious Calibration (SVC)) of the space sensor. This process is essential to minimize the combined effects of uncertainties affecting the space sensor calibration and those resulting from the inaccuracy of processing algorithms and models applied for the generation of data products. SVC is thus a fundamental element to maximize the return on investments for the Copernicus Program by delivering to the user science community satellite ocean colour data with accuracy granting achievement of target objectives from applications addressing environmental and climate change issues. The long-term Copernicus Program foresees multiple ocean colour missions (i.e., the Sentinel-3 satellites carrying the Ocean and Land Colour Instrument (OLCI)). The need to ensure the highest accuracy to satellite derived data products contributing to the construction of Climate Data Records (CDRs), suggests the realization, deployment and sustain of a European in situ infrastructure supporting SVC for Sentinel-3 missions, fully independent from similar facilities established and maintained by other space agencies (e.g., that operated in the Pacific Ocean by US agencies). It is emphasized that the need to cope with long-term Copernicus objectives on data accuracy, implies very stringent requirements for the in situ infrastructure and location providing reference measurements for SVC. These requirements, in fact, are much higher than those imposed by SVC for a single mission. The content of this Report, which is a revised version of a previous one (Zibordi et al. 2017), builds on the long-standing experience of the JRC on ocean colour radiometry. This experience counts on decadal field and laboratory measurements performed in support of validation and SVC applications, and additionally on activities comprehensively embracing measurement protocols, instruments characterization and the initiation of autonomous measurement infrastructures. Overall, this Report summarizes a number of recent investigations led by the JRC on SVC requirements for the creation of CDRs. The final objective is to consolidate in a single document the elements essential fJRC.D.2-Water and Marine Resource

System Vicarious Calibration for Copernicus Ocean Colour Missions: Requirements and Recommendations for a European Site

The Copernicus Program has been established through the Regulation EU No377/2014 with the objective to ensure long-term and sustained provision of accurate and reliable data on environment and security through dedicated services. Among these, the Copernicus Marine Environment Monitoring Service and the marine component of the Climate Change Service, both rely on satellite ocean colour observations to deliver data on water quality and climate relevant quantities such as chlorophyll-a concentration used as a proxy for phytoplankton biomass. Satellite ocean colour missions require in situ highly accurate radiometric measurements for the indirect calibration (so called System Vicarious Calibration (SVC)) of the space sensor. This process is essential to minimize the combined effects of uncertainties affecting the space sensor calibration and those resulting from the inaccuracy of processing algorithms and models applied for the generation of data products. SVC is thus a fundamental element to maximize the return on investments for the Copernicus Program by delivering to the user science community satellite ocean colour data with accuracy granting achievement of target objectives from applications addressing environmental and climate change issues. The long-term Copernicus Program foresees multiple ocean colour missions (i.e., the Sentinel-3 satellites carrying the Ocean and Land Colour Instrument (OLCI)). The need to ensure the highest accuracy to satellite derived data products contributing to the construction of Climate Data Records (CDRs), suggests the realization, deployment and sustain of a European in situ infrastructure supporting SVC for Sentinel-3 missions, fully independent from similar facilities established and maintained by other space agencies (e.g., that operated in the Pacific Ocean by US agencies). It is emphasized that the need to cope with long-term Copernicus objectives on data accuracy, implies very stringent requirements for the in situ infrastructure and location providing reference measurements for SVC. These requirements, in fact, are much higher than those imposed by SVC for a single mission. The content of this Report builds on the long-standing experience of the JRC on ocean colour radiometry. This experience counts on decadal field and laboratory measurements performed in support of validation and SVC applications, and additionally on activities comprehensively embracing measurement protocols, instruments characterization and the initiation of autonomous measurement infrastructures. Overall, this Report summarizes a number of recent investigations led by the JRC on SVC requirements for the creation of CDRs. The final objective is to consolidate in a single document the elements essential for the realization of a European SVC infrastructure in support of the Copernicus Program. Briefly, the various Chapters summarize: • General requirements for a long-term SVC infrastructure, which indicate the need for spatially homogenous oceanic optical properties, seasonal stability of marine and atmospheric geophysical quantities, negligible land perturbations, hyperspectral radiometry, and low measurement uncertainties; • Spectral resolution requirements for in situ SVC hyperspectral measurements as a function of bandwidths and center-wavelengths of most advanced satellite sensors, which specify the need for sub-nanometre resolutions to allow for supporting any scheduled satellite ocean color sensor; • Suitable SVC locations in European Seas showing the fitness of regions in the Eastern Mediterranean Sea to satisfy fundamental requirements.JRC.D.2-Water and Marine Resource

Ocean Colour Calibration and Validation: The JRC contribution to Copernicus

Copernicus Sentinel-3 missions, including the ongoing Sentinel-3A and -3B and the future Sentinel-3C and -3D, offer an unprecedented opportunity for long-term ocean colour observations to support global environmental and climate investigations. Nevertheless, any ocean colour mission incorporates calibration and validation activities essential for the indirect calibration of the space sensor and the validation of data products. These calibration and validation activities are largely centered on the production of highly accurate in situ reference measurements relying on state of the art measurement methods and instrumentation. Since the start of the operational ocean colour missions in 1997, the JRC sustained the required calibration and validation activities by developing unique expertise and setting up specific measurement programs and infrastructures. This expertise, measurement programs and infrastructures, currently support the Copernicus ocean colour calibration and validation tasks through the delivery and exploitation of in situ reference data essential for the quality control of satellite data products. This Technical Report aims at providing: i. a general introduction to the ocean colour paradigm; ii. an extended synopsis of requirements and strategies for satellite ocean colour missions with a detailed focus on the JRC experimental activities carried out during the last decades; and finally iii. a discussion supporting the need for a sustained support of the JRC laboratory and field measurement programs assisting the production and exploitation of in situ reference data for the validation of Sentinel-3 ocean colour products. The Report, mostly through section 2, should naturally satisfy readers interested in appraising the specific JRC activities performed to support ocean colour calibration and validation. The same Report through sections 1 and 3, should also satisfy the need for more essential information supporting the need for sustaining the JRC ocean colour validation activities currently embedded in the Copernicus Earth Observation program of major relevance for global marine and climate investigations.JRC.D.2-Water and Marine Resource

Toward an assessment of the fitness-for-purpose of Copernicus ocean colour data

The Copernicus Program has been established through the Regulation EU No377/2014 with the objective to ensure long-term and sustained provision of accurate and reliable data on environment and security through dedicated services. Among these, the Copernicus Marine Environment Monitoring Service and the marine component of the Climate Change Service, both rely on satellite ocean colour observations delivering data on water quality and climate relevant quantities such as chlorophyll-a concentration used as a proxy for phytoplankton biomass. This Report, building on the long-standing experience of the JRC on ocean colour, summarizes a number of recent investigations essential to assess the fitness-for-purpose of Copernicus ocean colour data products. These investigations embrace: i. The accuracy of radiometry data from the Ocean and Land Colour Instrument (OLCI) on board Sentinel-3a. The assessment is performed relying on geographically distributed in situ reference measurements from autonomous systems and dedicated oceanographic campaigns. ii. Uncertainty analysis of ocean colours radiometry data from a number of international missions. The analysis aims at assessing the potentials for the construction of Climate Data Records (CDRs) from independent missions. iii. The impact of adjacency effects in coastal data limiting the accuracy of ocean colour radiometry products. The study relies on state-of-the-art radiative transfer simulations and aims at quantifying adjacency effects in space data from sensors exhibiting different signal-to-noise ratios. iv. Uncertainties affecting in situ radiometry data as a result of the lack of comprehensive characterizations of field instruments. This is an attempt to illustrate the fundamental importance of comprehensive radiometric calibrations and characterizations for in situ instruments supporting validation activities. v. Reproducibility of the experimental determination of pigments concentrations for the validation of satellite data products. The analysis documents the differences affecting the quantification of pigments concentrations through the applicationJRC.D.2-Water and Marine Resource

Assessment of Copernicus OLCI Ocean Colour Data

The Copernicus Program has been established through the Regulation EU No377/2014 with the objective to ensure long-term and sustained provision of accurate and reliable data on environment and security through dedicated services. Among these, the Copernicus Marine Environment Monitoring Service and the marine component of the Climate Change Service, both rely on satellite ocean colour observations delivering data on water quality and climate relevant quantities such as chlorophyll-a concentration used as a proxy for phytoplankton biomass. This report summarizes results from activities carried out at the Joint Research Centre (JRC) to assess Copernicus Sentinel-3A and Sentinel-3B Ocean Land Colour Instrument (OLCI) radiometric data products in view of ensuring their confident use in environmental and climate applications.JRC.D.2-Water and Marine Resource