EyeOnWater Raspberry Pi: a do-it-yourself maker sensor system project to measure and classify natural water colour based on the Forel–Ule scale

Abstract. The EyeOnWater Raspberry Pi (EOW–RPI) is a do-it-yourself maker project for citizen science to measure and classify the natural colour of water. It describes the systematic development (from concept to the prototype and application) and evaluation of a replicable optical sensor system that enables the automatic determination of water's colour according to the Forel–Ule colour scale using a Raspberry Pi and associated camera. Within the framework of image data processing, the system was automated in accordance with the criteria of scientific methods such that application errors were minimised from the initial image acquisition to the colour analysis. The overarching purpose of this project was to promote the independence of scientifically interested and technically skilled laypersons in building their own research device and collecting and providing their own data through a community website. Furthermore, the project can serve as inspiration for the maker community with respect to the development of enhanced extensions. For this purpose, it is crucial that the documentation of software and hardware is made available as open-source information. In this project, we follow a systemic methodology that extends from the requirement analysis and conceptualisation phase through to the system architecture, with the aim of developing suitable hardware and software. To this end, the sensor system was implemented as a prototype and its technical feasibility; handling; and the scientific quality of data acquisition, processing, and Forel–Ule colour analysis were evaluated.