Abstract
Remote sensing by satellite-borne sensors presents a significant opportunity to enhance the spatio-temporal coverage of environmental monitoring programmes for lakes, but the estimation of classic water quality attributes from inland water bodies has not reached operational status due to the difficulty of discerning the spectral signatures of optically active water constituents. Determination of water colour, as perceived by the human eye, does not require knowledge of inherent optical properties and therefore represents a generally applicable remotely-sensed water quality attribute. In this paper, we implemented a recent algorithm for the retrieval of colour parameters (hue angle, dominant wavelength) and derived a new correction for colour purity to account for the spectral bandpass of the Landsat 8 Operational Land Imager (OLI). We used this algorithm to calculate water colour on almost 45,000 observations over four years from 1486 lakes from a diverse range of optical water types in New Zealand. We show that the most prevalent lake colours are yellow-orange and blue, respectively, while green observations are comparatively rare. About 40% of the study lakes show transitions between colours at a range of time scales, including seasonal. A preliminary exploratory analysis suggests that both geo-physical and anthropogenic factors, such as catchment land use, provide environmental control of lake colour and are promising avenues for future analysis.
Highlights
The colour of water as perceived by a human observer is intuitively associated with its suitability for consumption, quality of food collection, fitness for recreation, and aesthetic value, making it arguably one of the oldest water-quality attributes [1,2,3]
Each centroid was expanded to a circle area of interest (AOI) of 45 m radius and the AOI’s placement was inspected visually against aerial photos [32] to confirm or adjust its location over a central region of the lake away from islands or obvious shallow regions. 2334 lakes were excluded from the analysis, because the AOI could not be placed in openwater or the lakes were considered to be optically shallow, leaving a set of 1486 lakes
The relationships that we described between lake colour and catchment land use, lake elevation, and depth suggest that colour can be predicted from a suitable set of driver variables and future effort will be devoted to finding these relationships
Summary
The colour of water as perceived by a human observer is intuitively associated with its suitability for consumption, quality of food collection, fitness for recreation, and aesthetic value, making it arguably one of the oldest water-quality attributes [1,2,3]. Perceived colour is the physiological sensation originating from the sensitivity of the human eye to light in the spectral range of the primary colours red, blue, and green e.g., [5]. In the case of water, a medium that is not self-luminous, the light perceived by an observer is sunlight scattered back from within the water mass. This upwelling light is of a different colour than the incident solar radiation due to wavelength-dependent absorption and scattering of light by water and its constituents [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
