Monitoring water quality with a do-it-yourself modular instrument

Monitoring water transparency provides an indicator of the environmental status of the water body. One parameter to estimate the water transparency is the light diffuse attenuation coefficient (Kd) (Mobley, 1994). Historically, water transparency has been measured with a simple and inexpensive tool: The Secchi disk, a black and white disk that is lowered from above the water surface and tracked visually until it goes out of sight (Pitarch, 2020). Despite it being a valuable index of visual water clarity, the quality of its measurements is user-dependent, owing to differences between observers (Bruckner, 2018). In addition, ZSD (Secchi disk depth) measured data is discrete in time, and it is dependent on external factors such as water surface conditions and sunlight intensity. For this reason, we need electronic devices to get accurate measures and facilitate evaluations on a long-term scale for water quality monitoring. This need to develop novel approaches for monitoring environmental data is reflected in the recent growing attention toward citizen science (Njue et al., 2019). Citizen science is an expanding practice in which scientists and citizens actively collaborate to produce new knowledge for science and society (Vohland et al., 2021). Nowadays, we can find a wide range of projects to monitor aquatic ecosystems thanks to the progress in marine citizen science, especially enabled and promoted through technological developments (Garcia-Soto et al., 2021). Within the framework of H2020 MONOCLE project, it is developed the KduPRO, a cost-affordable and DIY (Do-It-Yourself) moored system evolved from the KdUINO (Bardaji et al, 2016). It is based on a modular system of light sensors, independent of each other, measuring the irradiance at different depths. The depth of each module can be modified according to the requirements of the project or the environment, offering to the user a custom array of sensors. To estimate Kd, the KduPRO measures the light intensity in