Abstract
AbstractInland and coastal waterbodies are critical components of the global biosphere. Timely monitoring is necessary to enhance our understanding of their functions, the drivers impacting on these functions and to deliver more effective management. The ability to observe waterbodies from space has led to Earth observation (EO) becoming established as an important source of information on water quality and ecosystem condition. However, progress toward a globally valid EO approach is still largely hampered by inconsistences over temporally and spatially variable in‐water optical conditions. In this study, a comprehensive dataset from more than 250 aquatic systems, representing a wide range of conditions, was analyzed in order to develop a typology of optical water types (OWTs) for inland and coastal waters. We introduce a novel approach for clustering in situ hyperspectral water reflectance measurements (n = 4045) from multiple sources based on a functional data analysis. The resulting classification algorithm identified 13 spectrally distinct clusters of measurements in inland waters, and a further nine clusters from the marine environment. The distinction and characterization of OWTs was supported by the availability of a wide range of coincident data on biogeochemical and inherent optical properties from inland waters. Phylogenetic trees based on the shapes of cluster means were constructed to identify similarities among the derived clusters with respect to spectral diversity. This typification provides a valuable framework for a globally applicable EO scheme and the design of future EO missions.
Highlights
Becoming established as an important source of information on water quality and ecosystem condition
The global importance of aquatic systems is incontestable since they play a fundamental role in biogeochemical cycling, the maintenance of biodiversity, and human wellbeing and prosperity (Galloway et al 2004; World Resources Institute 2005; Cole et al 2007; Borges et al 2015; Le Quere et al 2015) and as such are fundamental to the delivery of the UN Sustainable Development Goals
The aim of the present study is to extend our knowledge of the optical diversity of aquatic systems, and in particular inland waters
Summary
Becoming established as an important source of information on water quality and ecosystem condition. Phylogenetic trees based on the shapes of cluster means were constructed to identify similarities among the derived clusters with respect to spectral diversity This typification provides a valuable framework for a globally applicable EO scheme and the design of future EO missions. A range of parameters linked to the observed variability in water color has been encompassed in classification schemes These include water column parameters such as Secchi disk depth (ZSD, see Table 1 for a list of symbols and acronyms) (e.g., Arnone 1985), inherent optical properties (IOPs; mainly absorption: e.g., Babin et al 2003; Shi et al 2014) as well as radiometric quantities measured below or above the water surface (e.g., Le et al 2011; Moore et al 2014)
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