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The modern Forel-Ule scale: a 'do-it-yourself' colour comparator for water monitoring
Novoa, S.; Wernand, M.R.; van der Woerd, H.J. (2014). The modern Forel-Ule scale: a 'do-it-yourself' colour comparator for water monitoring. JEOS: RP 9: 14025 1-10.
In: Journal of the European Optical Society: Rapid Publications. European Optical Society: Hannover. ISSN 1990-2573, more
Peer reviewed article  

Available in Authors 

Author keywords
    Forel-Ule scale; water quality; participatory science; ocean colour; colourimetry; citizen science; water monitoring

Authors  Top 
  • Novoa, S., more
  • Wernand, M.R., more
  • van der Woerd, H.J.

    The colour comparator Forel-Ule scale has been used to estimate the colour of natural waters since the 19th century, resulting in one of thelongest oceanographic data series. This colour index has been proven by previous research to be related to water quality indicators suchas chlorophyll and coloured dissolved organic material. The aim of this study was to develop an affordable, ‘Do-it-Yourself’ colour scalethat matched the colours of the original Forel-Ule scale, to be used in water quality monitoring programs by citizens. This scale can bemanufactured with high-quality lighting filters and a white frame, an improvement with respect to the materials employed to manufacturethe original scale from the 19th century, which required the mixing of noxious chemicals. The colours of the new scale were matched tothe original colours using instrumental and visual measurements carried out under controlled lighting conditions, following the standardmeasurement protocols for colour. Moreover, the colours of the scale are expressed in Munsell notations, a standard colour system alreadysuccessfully used in water quality monitoring. With the creation of this Modern Forel-Ule scale, as a ‘Do-it-yourself’ kit, the authors foreseea possible use of the Forel-Ule number as a water quality index that could be estimated by means of participatory science and used byenvironmental agencies in monitoring programs.

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