Low-Cost Unmanned Aerial Multispectral Imagery for Siltation Monitoring in Reservoirs

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.

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

“…Many UAS aquatic remote sensing studies use Structure-from-Motion (SfM) photogrammetric techniques to stitch individual UAS images into ortho-and georectified mosaics (Arango and Nairn, 2019;Castro et al, 2020;McEliece et al, 2020;Olivetti et al, 2020). This approach applies matching key points from overlapping UAS imagery in camera pose estimation algorithms to resolve 3D camera location and scene geometry (Westoby et al, 2012;Arango et al, 2020).…”

“…Commonly used software (e.g. Pix4D) provide workflows that radiometrically calibrate, georeference, and stitch individual UAS images using a weighted average approach to create at-sensor reflectance 2D orthomosaics (Olivetti et al, 2020). L SR removal methods and water quality algorithms can be directly applied to reflectance orthomosaics to effectively derive water quality products of an entire water body.…”

“…UAS fill an operational gap between in situ and satellite remote sensing methods. While the current available commercial multispectral UAS sensor technology is geared toward terrestrial applications, mostly precision agriculture, the spectral bands have been useful in retrieving water quality parameters in aquatic water bodies (Choo et al, 2018;Arango and Nairn, 2019;Baek et al, 2019;Castro et al, 2020;Olivetti et al, 2020). A UAS sensor package designed for aquatic environments would undoubtedly improve remotely sensed retrievals and water quality measurements.…”

Application of Drone Technologies in Surface Water Resources Monitoring and Assessment: A Systematic Review of Progress, Challenges, and Opportunities in the Global South

“…The advent of drone technologies has seen the utility of sensors, such as Nikon (NIKKOR AF-S 24-85 mm f/3.5-4.5G ED VR) and the Nikon D800 [47], GoPro Hero 4 Black Edition [48], Feiyu Mini 3D Pro [48], Sony [44], and CMOS [49] to the multispectral sensors such as the MicaSense, Parrot Sequoia [28,[50][51][52][53][54][55] Sentera [38], MicaSense RedEdge multispectral [29,56], and the hyperspectral sensors such as Headwall Photonics Inc (207 bands), Ocean Optics STS-VIS (640 bands) [27], AvaSpec-dual Gaia (640 bands) [35,57], Sky-mini Nano-Hyperspec [30], Canon EOS 5DS R, and Headwall Nano-Hyperspec (640 bands) for local-scale water remote sensing applications (Table 2). However, as the spectral resolution of drone sensors increases, the associated costs also increase linearly.…”

Radiometric Correction of Multispectral UAS Images: Evaluating the Accuracy of the Parrot Sequoia Camera and Sunshine Sensor

“…In addition, Parrot provides instructions of how to perform sensor specific correction for vignetting [33] and how to calibrate for differences in exposure settings to convert the DN of the images to radiance using a unit (homogeneous to W•s −1 •m −2 ) common for all Parrot Sequoia cameras [34]. In several studies, radiometric correction of data collected with the Parrot Sequoia camera and sunshine sensor has been applied, e.g., to study post-fire recover of forests [35], for precision agriculture applications [36], and for siltation monitoring [37], albeit without explicitly studying the radiometric quality of the data.…”