Variability in specific-absorption properties and their use in a semi-analytical ocean colour algorithm for MERIS in North Sea and Western English Channel coastal waters

Tilstone, G.H.; Peters, S.W.M.; van der Woerd, H.J.; Eleveld, M.A.; Ruddick, K.; Schönfeld, W.; Krasemann, H.; Martinez-Vicente, V.; Blondeau-Patissier, D.; Röttgers, R.; Sørensen, K.; Jørgensen, P.V.; Shutler, J.D.

doi:10.1016/j.rse.2011.11.019

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Variability in specific-absorption properties and their use in a semi-analytical ocean colour algorithm for MERIS in North Sea and Western English Channel coastal waters

Tilstone, G.H.; Peters, S.W.M.; van der Woerd, H.J.; Eleveld, M.A.; Ruddick, K.; Schönfeld, W.; Krasemann, H.; Martinez-Vicente, V.; Blondeau-Patissier, D.; Röttgers, R.; Sørensen, K.; Jørgensen, P.V.; Shutler, J.D. (2012). Variability in specific-absorption properties and their use in a semi-analytical ocean colour algorithm for MERIS in North Sea and Western English Channel coastal waters. Remote Sens. Environ. 118: 320-338. http://dx.doi.org/10.1016/j.rse.2011.11.019

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VLIZ: Open Marine Archive 254212 [ download pdf ]

Keywords

Aquatic communities > Plankton > Phytoplankton
ANE, North Sea [Marine Regions]
Marine/Coastal

Author keywords

Case 2 waters; Inherent optical properties; Ocean colour remote sensing; Western English Channel

Authors		Top
Tilstone, G.H., more Peters, S.W.M. van der Woerd, H.J. Eleveld, M.A., more Ruddick, K., more	Schönfeld, W., more Krasemann, H. Martinez-Vicente, V., more Blondeau-Patissier, D.	Röttgers, R. Sørensen, K. Jørgensen, P.V. Shutler, J.D.

Abstract

Coastal areas of the North Sea are commercially important for fishing and tourism, and are subject to the increasingly adverse effects of harmful algal blooms, eutrophication and climate change. Monitoring phytoplankton in these areas using Ocean Colour Remote Sensing is hampered by the high spatial and temporal variations in absorption and scattering properties. In this paper we demonstrate a clustering method based on specific-absorption properties that gives accurate water quality products from the Medium Resolution Imaging Spectrometer (MERIS). A total of 468 measurements of Chlorophyll a (Chla), Total Suspended Material (TSM), specific- (sIOP) and inherent optical properties (IOP) were measured in the North Sea between April 1999 and September 2004. Chla varied from 0.2 to 35 mg m^- 3, TSM from 0.2 to 75 g m^- 3 and absorption properties of coloured dissolved organic material at 442 nm (a_CDOM(442)) was 0.02 to 0.26 m^- 1. The variation in absorption properties of phytoplankton (a_ph) and non-algal particles (a_NAP) were an order of magnitude greater than that for a_ph normalized to Chla (a_ph*) and a_NAP normalized to TSM (a_NAP*). Hierarchical cluster analysis on a_ph*, a_NAP* and a_CDOM reduced this large data set to three groups of high a_NAP*–a_CDOM, low a_ph* situated close to the coast, medium values further offshore and low a_NAP*–a_CDOM, high a_ph* in open ocean and Dutch coastal waters. The median sIOP of each cluster were used to parameterize a semi-analytical algorithm to retrieve concentrations of Chla, TSM and a_CDOM(442) from MERIS data. A further 60 measurements of normalized water leaving radiance (nL_w), Chla, TSM, a_CDOM(442) and a_NAP(442) collected between 2003 and 2006 were used to assess the accuracy of the satellite products. The regionalized MERIS algorithm showed improved performance in Chla and a_CDOM(442) estimates with relative percentage differences of 29 and 8% compared to 34 and 134% for standard MERIS Chla and a_dg(442) products, and similar retrieval for TSM at concentrations > 1 g^- 3.

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