The societal benefits of satellite ocean colour include aiding the management of the marine ecosystem, helping understand the role of the ocean ecosystem in climate change, aquaculture, fisheries, coastal zone water quality, and the mapping and monitoring of harmful algal blooms. Ocean colour is also designated as an essential climate variable by the Global Climate Observing System (GCOS). However, in order to have confidence in earth observation data, measurements made at the surface of the Earth, with the intention of providing verification or validation of satellite mounted sensor measurements, should be trustworthy and of the same high quality as those taken with the satellite sensors themselves. In order to be trustworthy, in situ validation measurements should include an unbroken chain of SI traceable calibrations and comparisons and full uncertainty budgets for each of the in situ sensors used. This metrological traceability is beginning to be demanded by the space agencies for satellite validation measurements and, for ocean colour, should follow the guidelines and protocols of the ESA Fiducial Reference Measurements for Satellite Ocean Colour (FRM4SOC) project (www.frm4soc.org). Until now, this has not been the case for most measurements used for validation, including those taken in the Aegean and Eastern Mediterranean. Subsequently, the Hellenic Centre for Marine Research (HCMR), in cooperation with the Laboratory of Optical Metrology (LOM), has started to follow the FRM direction by ensuring that the radiometers of its optical suite underwent SI-traceable absolute radiometric calibration. This included an estimate of the radiometry calibration uncertainty budget and was performed at the marine optical laboratory of the European Commission’s Joint Research Centre prior to their deployment on the recent PERLE-2 oceanographic cruise in the Eastern Mediterranean (Feb-Mar 2019). As well as irradiance and radiance sensors, the HCMR optical suite also houses instruments for measuring inherent optical properties (IOP) of the water column. Therefore, this paper presents the in-water radiometry matchups from PERLE-2 with Sentinel-3 Ocean and Land Colour Instrument (OLCI) measurements, and investigates their validation potential. It also presents the PERLE-2 cruise profile chlorophyll and backscatter measurements that aid this effort through characterizing the light scattering and absorbing constituents that contribute to the signal detected by satellite ocean colour sensors during validation matchups.
In the Aegean Sea and Eastern Mediterranean there are large discrepancies between in situ and satellite ocean colour
derived chlorophyll concentrations. The quantity that is monitored by ocean colour satellites and that can be used in the
estimation of chlorophyll concentration is the remote sensing reflectance, defined as the ratio of the water leaving
spectral radiance to the downwelling spectral irradiance. It can be determined in the field, with either above or in-water
radiance and irradiance measurements. The complex optical properties of the North-East Aegean Sea, including radiance
and irradiance, were studied during the AegeanMarTech project. Chlorophyll concentration estimates were derived from
simultaneous above and in-water radiometric measurements. These were validated against chlorophyll concentration
field data and compared against concurrent MODIS data from which chlorophyll was derived using two simple empirical
algorithms. It was found that the MedOC3 algorithm outperforms the operational OC3M-547 algorithm and produces the
least bias when compared against HPLC derived in situ chlorophyll. It is concluded that the greatest uncertainty in the
inversion arises due to CDOM absorption below the 488 nm band. The reflectance ratios indicated that there is always an
excess of yellow matter present in the study area and the water type could not be characterized optically as ‘’typical open
ocean” Case 1.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.