This study aims to develop Ocean Colour products of Inherent Optical Properties for Sentinel-3 OLCI.
There has been increasing interest over the last two decades in inverse methods dedicated to the estimation of Inherent Optical Properties (IOPs) of natural surface waters from Ocean Color remote sensing observations. The IOPs are determined by optical state equations of the constituents of seawater, including water molecules, phytoplankton, heterotrophic bacteria, viruses, non-algal particulate matter (organic detritus and mineral particles), gas bubbles, and coloured dissolved organic matter.
While the pure seawater IOPs are quasi constant (depending somewhat on water temperature and salinity), a large variability in aquatic bulk IOPs is tightly linked to variations in the concentration of different constituents, the size distribution and composition of particulate matter, including chemical composition of individual particles (refractive index), as well as composition of dissolved organic matter. These links make the IOPs the major carrier of information about various biogeochemically-important constituents of aquatic environments, for example the particulate and dissolved stocks of organic carbon and phytoplankton community structure.
Being able to retrieve IOPs from space observations of Ocean Color offers the particular benefit of improving the investigations of the biogeochemical status of the aquatic surface layers at large basin and regional scales over long periods of time, beyond the application of the standard satellite data product of chlorophyll-a concentration, Chl.
For this reason, the IOPs are now included in a suite of Essential Climate Variables (ECVs) in the frame of the Climate Change Initiative international program. Satellite-derived IOP products have been used in many studies addressing various characteristics of aquatic constituents of biogeochemical significance, primary production, water quality, and characterisation of water masses and other physical processes.
The objective of the study is to develop Ocean Colour products of Inherent Optical Properties for Sentinel-3 OLCI and to validate them via a community review process.
In the frame of this project, different IOPs algorithms suitable to the OLCI spectral bands are being selected and implemented after consultation with a representative panel of expert and end-users.
While there are existing algorithms that can directly be applied to the OLCI spectral bands, the potential offered by the extended spectral coverage of OLCI is being analysed, and research is performed to account for such specifics within the IOPs retrieval algorithm (and associated accuracy).
A specific metric to be used for the IOP product evaluation is being developed and submitted to the panel review for agreement, prior to the validation: the selected algorithms are being implemented and evaluated against different, but complementary, IOPs data sets (synthetic, in situ, and match-up).
A prototype of the resulting OLCI Inherent Optical Properties (IOPs) ATBD will be delivered, dealing with the waters in open ocean, regional seas, coastal areas and inland, as per the consensus of the international Ocean Colour Scientific community which has been reached in the last 10 years, in order to complement the EO products that are supplied with MODIS and VIIRS measurements or with the past missions’ products (MERIS, SeaWIFS, etc.) (Figure 1, top right, click to expand).
A standard iterative development process will be applied:
- Definition of IOP product requirements.
- Design of a state-of-the-art algorithm by testing various hypothesis and related solutions.
- Coding of a data processor prototype, inclunding validation of its outputs, in a ‘community’ framework (involving the scientific community in the review process).
The work is divided in five work packages (WPs).
Studies will start with the first WP, which is dedicated to the review of user requirements for marine IOP products, with attention to the OLCI specific capabilities.
The second WP will focus on the development of the algorithms.
The third WP is the implementation of the algorithm(s) in the form of data processor prototype.
The validation of products, and a fortiori the selected data processor, is performed in WP4, and WP5 is dedicated to the organization of the community/user reviews.
Most important are the tasks related to the development of IOP algorithms, their intercomparisons, and the selection of the best approach. Though mainly in WP2, it is an iterative process which requires the implementation of the algorithms in data processors for processing of global OLCI-IOP data (WP3) and performing validation tasks (WP4) whose results are submitted to the panel of international experts (WP5).
|WP1||Review of user requirements for marine IOP products, with the attention to the OLCI specific capabilities.|
|WP2||Development of a state-of-the-art IOP algorithm for OLCI.|
|WP3||Software prototype of the IOP algorithms.|
|WP4||Validation of the IOP products.|
|WP4||Organisation of the community/user review process.|
|Phase||Date and location|