Investigating small unoccupied aerial systems (sUAS) multispectral imagery for total suspended solids and turbidity monitoring in small streams

Abstract

Small unoccupied aerial systems (sUAS) are increasingly used for field data collection and remote sensing purposes. Their ease of use, ability to carry sensors, low cost, precise manoeuvrability and navigation makes them versatile tools. The goal of this study is to investigate if sUAS multispectral imagery can be utilized to measure turbidity and total suspended solids (TSS) of small streams. sUAS multispectral imagery and water samples at varying depths were collected before and after rain events on three sampling dates in 2019 from Moores Creek in Lanett, Alabama (AL), United States of America (USA), which was restored in 2017. The water samples were processed for TSS and turbidity and related to pixel values from the multispectral imagery. Linear regression was used to develop models for TSS and turbidity. The models were then tested on Moores Mill Creek in Chewacla State Park, AL, USA. For Lanett, TSS and turbidity regression models for low flows had coefficients of determination (R 2) values of 0.77 and 0.78, respectively. During high flows, different single bands and band ratios were required for comparable R 2 values, suggesting separate models may be needed for high and low flow events. When the Lanett models were applied to Chewacla State Park, predicted TSS and turbidity were not comparable to measured values indicating that location-specific models may be required. Future research should incorporate depth as a variable since streambed visibility likely impacts results, along with other modelling and data analysis methods, such as machine learning.

Measuring High Levels of Total Suspended Solids and Turbidity Using Small Unoccupied Aerial Systems (sUAS) Multispectral Imagery

“…Sampling with respect to exact location and depth was not achieved with no account for how the streambed might influence results. Despite these limitations, results agreed with similar previous studies such as [29,32]. Prior et al [32] also used sUAS multispectral imaging for TSS and turbidity modeling, but in a small stream setting along with cross-site model testing.…”

“…Despite these limitations, results agreed with similar previous studies such as [29,32]. Prior et al [32] also used sUAS multispectral imaging for TSS and turbidity modeling, but in a small stream setting along with cross-site model testing. Low and high flow events were modeled separately because different single bands and band ratios were significant.…”

“…In contrast, Prior et al [32] showed that separate models were required to relate sUAS multispectral imagery to TSS for cases with low and high sediment loads due to stream flow variation. Even with elevated suspended sediment levels present during high flow events, the models still struggled, likely due to influence from stream bed reflectance.…”

“…All statistical analyses were performed in SAS (SAS, Cary, NC, USA) [41,42] and Matlab 2020a (Mathworks, Natick, MA, USA). The above methods of developing unique TSS and turbidity models from multispectral data followed procedures from Prior et al [32].…”

“…Note that the blue rectangle in each map is the lamella plate settler and the blue shading that perpendicularly transects the sediment basin is three rows of wire backed coir baffles attached to metal posts dividing the basin into four sections. Lastly, reflectance values along with TSS and turbidity measurements from this study and from Prior et al [32] were compared ( Figure 6).…”