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The NERC and CEH trade marks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. The growth of mass populations of toxin-producing cyanobacteria is a serious concern for the 2 ecological status of inland waterbodies and for human and animal health. In this study we 3 examine the performance of four semi-analytical algorithms for the retrieval of chlorophyll a 4 (Chl a) and phycocyanin (C-PC) from data acquired by the Compact Airborne Spectrographic 5Imager-2 (CASI-2) and the Airborne Imaging Spectrometer for Applications (AISA) Eagle 6Sensor. The retrieval accuracies are compared to those returned by semi-empirical band-ratio 7 algorithms optimised for these datasets. The best-performing algorithm for the retrieval of 8Chl a was a semi-empirical band-ratio model (R 2 = 0.832; RMSE = 29.8%). The best 9 performing model for the retrieval of C-PC was a semi-analytical nested band ratio model (R 2 10 = 0.984; RMSE = 3.98 mg m -3 ). The concentrations of C-PC retrieved using the semi-11 analytical model were also correlated with those of cyanobacterial cells (R 2 = 0.380) and of 12 the particulate and total (particulate plus dissolved) pools of microcystins (R 2 = 0.858 and 13 0.896 respectively). Importantly, both the semi-empirical and semi-analytical algorithms 14 were able to retrieve the concentration of C-PC at cyanobacterial cell concentrations below 15 current warning thresholds for cyanobacteria in waterbodies. This demonstrates the potential 16 of remote sensing to contribute to early-warning detection and monitoring of cyanobacterial 17 blooms for human health protection, at regional and global scales. 18 19

Inland 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 5 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.

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Time-series airborne remote sensing was used to monitor diurnal changes in the spatial distribution of a bloom of the potentially toxic cyanobacterium Microcystis aeruginosa in the shallow eutrophic waters of Barton Broad, United Kingdom. High spatial resolution images from the Compact Airborne Spectrographic Imager (CASI-2) were acquired over Barton Broad on 29 August 2005 at 09:30 h, 12:00 h, and 16:00 h Greenwich mean time. Semiempirical water-leaving radiance algorithms were derived for the quantification of chlorophyll a (R 2 5 0.96) and C-phycocyanin (R 2 5 0.95) and applied to the CASI-2 imagery to generate dynamic, spatially resolving maps of the M. aeruginosa bloom. The development of the bloom may have been fostered by a combination of the recent improvements in the ambient light environment of Barton Broad, allied to the acute depletion of bioavailable nutrient pools, and stable hydrodynamic conditions. The vertical distribution of M. aeruginosa was highly transient; buoyant colonies formed early morning and late afternoon near-surface aggregations across the lake during periods of nonturbulent mixing (wind speed ,4 m s 21 ). However, the extent of these near-surface aggregations was highly spatially variable, and nearshore morphometry appeared to be crucial in creating localized regions of nonturbulent water in which pronounced and persistent near-surface aggregations were observed. The formation of these near-surface scums would have been vital in alleviating light starvation in the turbid waters of Barton Broad. The calm water refuges in which persistent near-surface accumulations occurred may have been an important factor in determining the persistence of the bloom.