Spectral Response of Water Under Different Concentrations of Suspended Sediment: Measurement and Simplified Modeling

Abstract

Understanding the spectral behaviour of water is of the greatest importance to the quality management of water resources. Continuous monitoring by remote sensing is therefore essential for administrators seeking the efficient management of its many uses. The aim of this research was to characterise the spectral response of water submitted to different concentrations of sediments of varying textural properties, organic matter and salts, and to identify the implications of these characteristics using simplified modelling. The experiment was conducted at the Radiometry Laboratory of the Department of Agricultural Engineering of the Federal University of Ceará, Brazil. The soils used in the research came from two areas of irrigated agriculture in Ceará, one in Morada Nova and the other in Pentecoste. Both soils were classified as Fluvic Neosols; the first saline and the second saline-sodic, and presented significant differences in granulometric composition and organic matter content. From the results, it can be concluded that: (i) sediments added at different concentrations cause an increase and deformation of the reflectance curves, and that maximum spectral partitioning occurs at two reflectance peaks; (ii) derivative analysis favours the identification of wavelengths that best differentiate sediment concentration, allowing more-efficient modelling of the process; (iii) the characteristics of texture, organic matter and salt content have little effect on estimating suspended-sediment concentration in the water, making multiple linear regression modelling a viable option for this purpose.