Small unmanned aerial systems (sUAS) are becoming increasingly popular due to their affordability and logistical ease for repeated surveys. While sUAS-based remote sensing has many applications in water resource management, their applicability and limitations in fluvial settings is not well defined. This study uses a combined thermal-optic sUAS to monitor the seasonal geothermal influence of a 1-km-long reach of the Yellowstone River, paired with in-situ streambed temperature profiles to evaluate geothermal seep interactions with Yellowstone River in Montana, USA. Accurate river water surface elevation along the shoreline was estimated using structure from motion (SfM) photogrammetry digital surface models (DSMs); however, water surface elevations were unreliable in the main river channel. Water temperature in thermal infrared (TIR) orthomosaics was accurate in temperature ranges of tens of degrees (>≈30 °C), but not as accurate in temperature ranges of several degrees (>≈15 °C) as compared to in-situ water temperature measurements. This allowed for identification of geothermal features but limited the ability to identify small-scale temperature changes due to river features, such as pools and riffles. The study concludes that rivers with an average width greater than or equal to 123% of the ground area covered by a TIR image will be difficult to study using structure from motion photogrammetry, given Federal Aviation Administration (FAA) altitude restrictions and sensor field of view. This study demonstrates the potential of combined thermal-optic sUAS systems to collect data over large river systems, and when combined with in-situ measurements, can further increase the sUAS utility in identifying river characteristics.
Beaver dam analogs (BDAs) are being installed on streams where restoration goals include reconnecting the stream to its floodplain, increasing water storage in the stream corridor, and improving the extent and vigor of riparian vegetation. This study evaluated the effects on vegetation vigor of a BDA treatment on Blacktail Creek in southwest Montana, USA, using data from Sentinel-2 satellites and a small unmanned aerial system (sUAS; a.k.a. drone). The goal of this research was to determine if BDA installation increased the health of riparian vegetation. Sentinel-2 remote sensing data from 2016 to 2021 were used to compare the pre- and post-treatment periods, and to evaluate effects in the treated area relative to control areas. Enhanced Vegetation Index (EVI) values were calculated to quantify vegetation response from the addition of BDAs. These data suggest that installing BDAs at this site has not led to an apparent increase in late-summer vegetation vigor relative to the controls. One potential explanation for these results is that the vegetation was not water limited prior to treatment in this study reach. This is an important consideration for water resource managers prior to installation of BDAs if the main restoration goal is the improvement of riparian vegetation health. Two high spatial resolution sUAS multispectral datasets were collected to evaluate the bias introduced by using the relatively course resolution (10 m) satellite imagery to assess these changes. High-resolution sUAS data allow fine-scale differences in vegetation and inundated area to be distinguished; however, historical sUAS datasets are rarely available. Satellite-based remote sensing has much lower resolution; however, Sentinel-2 satellite data have been available for the entire earth since 2016. This study demonstrates that the combination of sUAS and satellite based remote sensing data provides a method to compare high-resolution datasets for spatial analysis while gaining insight into relatively low-resolution historical data for temporal analysis.
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