Abstract
The recent and continuous development of unmanned aerial vehicles (UAV) and small cameras with different spectral resolutions and imaging systems promotes new remote sensing platforms that can supply ultra-high spatial and temporal resolution, filling the gap between ground-based surveys and orbital sensors. This work aimed to monitor siltation in two large rural and urban reservoirs by recording water color variations within a savanna biome in the central region of Brazil using a low cost and very light unmanned platform. Airborne surveys were conducted using a Parrot Sequoia camera (~0.15 kg) onboard a DJI Phantom 4 UAV (~1.4 kg) during dry and rainy seasons over inlet areas of both reservoirs. Field measurements of total suspended solids (TSS) and water clarity were made jointly with the airborne survey campaigns. Field hyperspectral radiometry data were also collected during two field surveys. Bio-optical models for TSS were tested for all spectral bands of the Sequoia camera. The near-infrared single band was found to perform the best (R2: 0.94; RMSE: 7.8 mg L−1) for a 0–180 mg L−1 TSS range and was used to produce time series of TSS concentration maps of the study areas. This flexible platform enabled monitoring of the increase of TSS concentration at a ~13 cm spatial resolution in urban and rural drainages in the rainy season. Aerial surveys allowed us to map TSS load fluctuations in a 1 week period during which no satellite images were available due to continuous cloud coverage in the rainy season. This work demonstrates that a low-cost configuration allows dense TSS monitoring at the inlet areas of reservoirs and thus enables mapping of the sources of sediment inputs, supporting the definition of mitigation plans to limit the siltation process.
Highlights
Conventional monitoring of water quality in lakes and reservoirs relies on frequently conducted pointwise limnologic surveys but usually fails to capture the spatial variability of the underlying processes [1]
Remote sensing techniques over inland waters are based on the analysis of water optical properties, such as the apparent and inherent optical properties, and of the optically active components (OAC)—total suspended solids (TSS), chlorophyll-a (Chl-a), and colored dissolved organic matter (CDOM)—by applications of either empirical, semi-empirical, semi-analytical, quasi-analytical, or analytical bio-optical models [4]
It can be seen that the selection of the model is an important step, as the results present a wide range of TSS concentrations
Summary
Conventional monitoring of water quality in lakes and reservoirs relies on frequently conducted pointwise limnologic surveys but usually fails to capture the spatial variability of the underlying processes [1]. Remote sensing is increasingly used to fill gaps in conventional monitoring thanks to its capacity to acquire spatialized data and to the ability to generate long time series by combining information from different sensors [2,3]. Despite advances in the use of remote sensing, there are a series of limitations in the application of orbital images for inland water quality monitoring:. Manned aerial missions have been applied for inland water quality monitoring, seeking more detailed mapping of the OAC with high precision [7]. This resource has high operational costs and, when surveys are realized at a high flight altitude, atmospheric corrections cannot be overlooked [8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
