CoastColour Round Robin data sets: a database to evaluate the performance of algorithms for the retrieval of water quality parameters in coastal waters

Bouchra Nechad ,Carolina Sá ,Yu-Hwan Ahn ,Rüdiger Röttgers ,David G Foley ,Kevin Ruddick ,Isabel Caballero ,Mhd Suhyb Salama ,Stéphane Maritorena ,Tawnya D Peterson ,Jasmine Nahorniak ,David Blondeau-Patissier ,Andrew Clive Banks ,P Jeremy Werdell ,Arnold G Dekker ,Vittorio E Brando ,Lesley Clementson ,Kadija Oubelkheir ,A Siliò-Calzada ,Nagur Cherukuru ,Marco Peters ,Gavin H Tilstone ,Thomas Schroeder ,Z Lee ,Morgaine Mckibben ,Vanda Brotas ,Victor Martínez-Vicente ,Carsten Brockmann

doi:10.5194/essd-7-319-2015

Abstract

Abstract. 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.

Highlights

Several studies on the intercomparison of ocean colour algorithms have been carried out to provide recommendations on appropriate methodologies and identify the domains of applicability and limitations or weaknesses of the algorithms, e.g. O’Reilly et al (1998), Maritorena et al (2006), Brewin et al (2015), Odermatt et al (2012), and Werdell et al (2013)
The distributions of water depth, temperature and salinity, chlorophyll a (CHL) and total suspended matter (TSM) concentrations, inherent optical properties (IOPs), and AOPs are presented in Sects. 3.1–3.6, followed by the analysis of the covariation between CHL and TSM and bio-optical relationships existing in the CoastColour Round Robin (CCRR) data sets (Sect. 3.7)
The bio-optical relationships within the match-up field and in situ data sets are compared to the models, as well as to the ranges of TSM, CHL, and CDOM concentrations assumed in the simulated CCRRv1

Summary

Introduction

Several studies on the intercomparison of ocean colour algorithms have been carried out to provide recommendations on appropriate methodologies and identify the domains of applicability and limitations or weaknesses of the algorithms, e.g. O’Reilly et al (1998), Maritorena et al (2006), Brewin et al (2015), Odermatt et al (2012), and Werdell et al (2013). The diversity of approaches is especially high in case 2 waters (Morel and Prieur, 1977) with higher complexity of the optical properties and larger ranges of in-water constituent concentrations To understand how these elements can affect the performance of algorithms, the CoastColour Round Robin (CCRR) project was designed (Ruddick et al, 2010). The CCRR uses a variety of reference data sets to test algorithms and compare their accuracy for retrieving water quality (WQ) parameters These WQ parameters include chlorophyll a (CHL) and total suspended matter (TSM) concentrations, inherent optical properties (IOPs), underwater light attenuation coefficients such as the diffuse attenuation of the downwelling irradiance (Kd) or the photosynthetically available radiation (PAR) with which a set of satellite data processing quality flags are associated

Methods

Results

Conclusion