AUTHOR=Brewin Robert J. W. , Sun Xuerong , Wood Joanne L. , Brewin Thomas G. , McBride Delaney , Frensley B. Troy , Bresnahan Philip J. , Simis Stefan G. H. , Schmidt Norbert , George Grinson , Stoy Ancy C. , Menon Nandini N. , Chekidhenkuzhiyil Jasmin , Abdulaziz Anas , Sathyendranath Shubha , Krug Lilian A. , Das Nabanita , Sarker Subrata , Pasche Natacha , Haller Laurence , Ghadyani Yasmin , Odermatt Daniel , Camus Alexandre , Mader Suzanne , Bonny Adrien , Pochelon Alexis , Akinnigbagbe Akintoye Edward , Noernberg Mauricio Almeida , Mahu Edem , Diankha Ousmane , Gonzalez-Silvera Adriana , Ahmed Waqar , Kidwai Samina , Hernandez-Moresino Rodrigo , Mohamed Ahmed Hussein , Panassa Wilfried Essowè , Purba Noir Primadona , Betancur-Turizo Stella Patricia , Bernawis Lamona Irmudyawati , Smeti Houssem , Moshi Happiness Anold 

TITLE=An innovation of two established methods for monitoring water colour and clarity: participatory science using the mini- and midi- secchi disks

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 13 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2025.1610130

DOI=10.3389/fenvs.2025.1610130

ISSN=2296-665X

ABSTRACT=Measurements of water colour and clarity are used to track the environmental status of lakes, estuaries and oceans. The oldest standardised methods for measuring water clarity and colour are the Secchi disk and Forel-Ule colour scale. Both techniques were developed in the 19th century and require use of the human eye. Despite the advent of optoelectronic-based sensing, these visual methods are still used today, owing to their sensitivity, affordability, simplicity and long history of use. Recently, a hand-held device was developed for measuring the Secchi depth and Forel-Ule colour (presented in two formats, named the mini- and midi-Secchi disk). Designed to be small, light and convenient-to-use, it is well suited for participatory science projects that involve monitoring water colour and clarity. To date, over 900 mini- and midi-Secchi disks have been distributed to citizens and scientists, primarily through six projects, with data mostly transferred via mobile phone applications to data servers and dashboards. In this paper, we describe the methods used in the projects and show some characteristics of the datasets collected so far. We showcase how the device can be used for scientific applications, such as verifying satellite data products, gaining new scientific insights, and supporting public engagement and education. Finally, we provide suggestions for methodological improvements and future developments.