Integrated workflow for use of unmanned aerial vehicles in monitoring water resources

Unmanned aerial vehicles (UAVs) offer possibilities to enhance monitoring of river basins, wetlands, and other important water bodies. Opportunities to use UAVs in environmental studies include periodic and autonomous flights to detect and provide warnings of algal blooms, access to areas that are difficult to explore, and more rich data sets of water coverage, vegetation, and other features. In order to benefit from UAV technology, appropriate flight planning, data collection, and post-flight data processing strategies must be developed. In this study, we present recommendations for integrating UAVs into the study of water bodies. We first provide an overview of the key aspects of flight planning that take into account the desired accuracy and number of images required. Given the computational resources required to generate aerial maps, we consider merging of adjacent point clouds. We evaluate ground control point placement to connect maps into existing coordinate systems and improve map accuracy. The workflow is demonstrated using a river basin located in an urban setting that is bound on both sides by flood-control levees. A 2.7 ha area was mapped using 200 images with a ground sampling distance of approximately 1.65 cm/pixel. Average root mean square error along the levees was 3.1cm in the horizontal plane, and 6.9cm in the vertical direction. Error near the river was much higher (35-40cm), suggesting more control points be placed near water bodies. The results of this study demonstrate that UAVs can be introduced into water resource monitoring, but that UAV integration into current projects requires planning, resource investment, and education on the part of the users of such technology.