Estimating the Underwater Diffuse Attenuation Coefficient with a Low-Cost Instrument: The KdUINO DIY Buoy

Raul Bardaji,Jaume Piera,Marcel Wernand,Carine Simon,Albert-Miquel Sánchez

doi:10.3390/s16030373

Abstract

A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility.

Highlights

IntroductionOne parameter to quantify water transparency is the diffuse attenuation coefficient (Kd ), which is estimated by measuring the decrease of downwelling irradiance with depth
Water transparency is a common indicator to assess the environmental status of water bodies as it is strongly affected by different water quality components such as the concentration of phytoplankton or dissolved organic and inorganic components [1,2].One parameter to quantify water transparency is the diffuse attenuation coefficient (Kd ), which is estimated by measuring the decrease of downwelling irradiance with depth
When applied to a liquid medium, it states that the light intensity decreases exponentially as a function of depth which is mathematically written as: E2 “ E1 eKd ∆z where E2 is the irradiance of the light at depth z2, E1 is the irradiance of the light at depth z1, and

Summary

Introduction

One parameter to quantify water transparency is the diffuse attenuation coefficient (Kd ), which is estimated by measuring the decrease of downwelling irradiance with depth. About 90% of the diffusely reflected light from the water column comes from a surface layer at a depth 1/Kd [1], making. Kd a key parameter to correctly interpret remote sensing data. From the operational point of view, Kd is a very practical parameter to use as it is computed from relative changes of irradiances (see Figure 1), and does not require the absolute radiometric calibration of sensors. KdUINO’s design and computation of Kd as the slope of the linear regression regression ofofthe measurements.

Methods

Results

Conclusion