title: True colour classification of natural waters with medium-spectral resolution satellites: SeaWiFS, MODIS, MERIS and OLCI.
abstract: The colours from natural waters differ markedly over the globe, depending on the water composition and illumination conditions. The space-borne "ocean colour" instruments are operational instruments designed to retrieve important water-quality indicators, based on the measurement of water leaving radiance in a limited number (5 to 10) of narrow (≈10 nm) bands. Surprisingly, the analysis of the satellite data has not yet paid attention to colour as an integral optical property that can also be retrieved from multispectral satellite data. In this paper we re-introduce colour as a valuable parameter that can be expressed mainly by the hue angle (α). Based on a set of 500 synthetic spectra covering a broad range of natural waters a simple algorithm is developed to derive the hue angle from SeaWiFS, MODIS, MERIS and OLCI data. The algorithm consists of a weighted linear sum of the remote sensing reflectance in all visual bands plus a correction term for the specific band-setting of each instrument. The algorithm is validated by a set of 603 hyperspectral measurements from inland-, coastal- and near-ocean waters. We conclude that the hue angle is a simple objective parameter of natural waters that can be retrieved uniformly for all space-borne ocean colour instruments.
authors.affiliation: Royal Netherlands Institute for Sea Research, Physical Oceanography, Marine Optics & Remote Sensing, PO box 59, Den Burg1790AB, Texel, The Netherlands. Hans.van.der.Woerd@nioz.nl.|Institute for Environmental Studies (IVM), VU University Amsterdam, De Boelelaan 1087, Amsterdam 1081HV, The Netherlands. Hans.van.der.Woerd@nioz.nl.
authors.forename: Hendrik J van der
authors.initials: HJ
authors.lastname: Woerd
authors.affiliation: Royal Netherlands Institute for Sea Research, Physical Oceanography, Marine Optics & Remote Sensing, PO box 59, Den Burg1790AB, Texel, The Netherlands. Marcel.Wernand@nioz.nl.
authors.forename: Marcel R
authors.initials: MR
authors.lastname: Wernand
keywords: MERIS; MODIS; OLCI; SeaWiFS; citizen science; colourimetry; hue angle; ocean colour remote sensing; spectral bands; water quality