Abstract
Rapid and widespread monitoring of inland and coastal water quality occurs through the use of remote sensing and near-surface water quality sensors. A new addition is the development of smartphone applications (Apps) to measure and record surface reflectance, water color and water quality parameters. In this paper, we present a field study of the HydroColor (HC, measures RGB reflectance and suspended particulate matter (SPM)) and EyeOnWater (EoW, determines the Forel–Ule scale—an indication to the visual appearance of the water surface) smartphone Apps to evaluate water quality for inland waters in Eastern Australia. The Brisbane river, multiple lakes and reservoirs and lagoons in Queensland and New South Wales were visited; hyperspectral reflection spectra were collected and water samples were analysed in the laboratory as reference. Based on detailed measurements at 32 sites, covering inland waters with a large range in sediment and algal concentrations, we find that both water quality Apps are close, but not quite on par with scientific spectrometers. EoW is a robust application that manages to capture the color of water with accuracy and precision. HC has great potential, but is influenced by errors in the observational procedure and errors in the processing of images in the iPhone. The results show that repeated observations help to reduce the effects of outliers, while implementation of camera response functions and processing should help to reduce systematic errors. For both Apps, no universal conversion to water quality composition is established, and we conclude that: (1) replicated measurements are useful; (2) color is a reliable monitoring parameter in its own right but it should not be used for other water quality variables, and; (3) tailored algorithms to convert reflectance and color to composition could be developed for lakes individually.
Highlights
Surface freshwater is a finite resource essential for human and ecosystem existence
The results show that the measurements taken across the 13 water bodies have covered a wide range of water qualities from oligotrophic to hypertrophic
The spread3o.1f.CWHateLr Qleuvaeliltsy Csuongdgiteiosntss that the majority of sites included within this study have relatively low chlorophyllInaTcaobnlecSe1n, tarsautmiomnasr.yTohf tehemmaejoanriltayboorfatsoirtyesreasureltswfoitrhCiHnLthaned1S.5PMμgco/Lnc(eLnatrkateioSntsCislgaiivre)nt,o 26 μg/L
Summary
Surface freshwater is a finite resource essential for human and ecosystem existence. Adequate freshwater quality and quantity is required for sustainable development necessary for human consumption, irrigation, fishing and recreational use [1,2]. To monitor the thousands of natural lakes, freshwater reservoirs, billabongs and river systems in Australia, a system is required that is able to access these waters with high spatial and temporal resolution. Wernand et al [25] introduced a new parameter that can be retrieved accurately from the MERIS ocean color sensor—the Forel–Ule index (FUI). This FUI is a discrete number system developed at the start of the 20th century to quantify the color of water, as perceived by the human eye. IInn 22001144,, tthhee EEyyeeOOnnWWaatteerr ((EEooWW)) aanndd HHyyddrrooCCoolloorr ((HHCC)) ssmmaarrttpphhoonnee aapppplliiccaattiioonnss ((AAppppss)) bbeeccaammee aavvaaiillaabbllee ttoo mmeeaassuurree tthhee ccoolloorr ooff wwaatteerr. TThhee aaccccuurraaccyy aanndd pprreecciissiioonn ooff wwaatteerr ccoolloorr mmeeaassuurreemmeennttss ffoorr wwaatteerr qquuaalliittyy ffrroomm tthhee ttwwoo ssmmaarrttpphhoonnee aapppplliiccaattiioonnss ffoorr cciittiizzeenn sscciieennccee wweerree rreeffeerreenncceedd totorerfleeflcetcatnacnecme emaseuarseumreemntesnmtsadmeawdeithwaitshtanadsatradnudnadrderwunadteerrswpaetcetrrosrapdeciotrmoeratedri.oFmineatellry., Fainndalwlyh, earnedawpphreorperaiaptpe,rothperiaptoet,etnhteiapl ofoternwtiaaltefrorcowloartemr ecaoslourremmeeanstusretomdenertsivteoodthereirvewoatthererqwuaaltietyr qpuaraalimtyetpearrsaims detiescrsusisseddis. cussed
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