Fundamentals of in Situ Digital Camera Methodology for Water Quality Monitoring of Coast and Ocean

Lonneke Goddijn-Murphy,Dave Bowers,Damien Dailloux,Martin White

doi:10.3390/s90705825

Abstract

Conventional digital cameras, the Nikon Coolpix885® and the SeaLife ECOshot®, were used as in situ optical instruments for water quality monitoring. Measured response spectra showed that these digital cameras are basically three-band radiometers. The response values in the red, green and blue bands, quantified by RGB values of digital images of the water surface, were comparable to measurements of irradiance levels at red, green and cyan/blue wavelengths of water leaving light. Different systems were deployed to capture upwelling light from below the surface, while eliminating direct surface reflection. Relationships between RGB ratios of water surface images, and water quality parameters were found to be consistent with previous measurements using more traditional narrow-band radiometers. This current paper focuses on the method that was used to acquire digital images, derive RGB values and relate measurements to water quality parameters. Field measurements were obtained in Galway Bay, Ireland, and in the Southern Rockall Trough in the North Atlantic, where both yellow substance and chlorophyll concentrations were successfully assessed using the digital camera method.

Highlights

Remote sensing offers a useful way to monitor water resources over different space and time scales
The response spectra illustrated that both digital cameras are fundamentally three-band radiometers, with bands centred on wavelengths in the red, green and blue parts of the visible spectrum
It was concluded that a conventional digital camera can act as a simple but practical three-band radiometer

Summary

Introduction

Remote sensing offers a useful way to monitor water resources over different space and time scales. On the order of 1 km, while useful in shelf seas, cannot be used in coastal areas and inland waters where shallow water and land borders contaminate the images. In such regions, in situ or airborne mounted systems must be employed. The use of relatively complex multi-spectral instruments may be costly, . This current study explores the possibilities of employing a conventional digital camera, as an alternative low-cost technique, to estimate water composition from optical properties of the water surface

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