A Bird's Eye View of Fish Habitat: Use of High Resolution Low Altitude Aerial Photography in Assessments of Salmonid Habitat in Streams

Aerial photography has been used for decades to evaluate changes in the landscape; however the low resolution of these photos limits their use in documenting changes in stream morphology relevant to fishes. More recently high resolution digital photography and different platforms such as blimps and unmanned aerial vehicles (UAVs) have been demonstrated to provide information of stream bathymetry, sediment types, large wood and riparian vegetation at a resolution that might prove informative at describing fish habitat and that can be processed in a GIS environment.  In-stream habitat surveys provide higher resolution information but over a more limited extent than can be sampled using aerial platforms.  In this study, we explore the use of aerial photography collected from UAVs and blimps to in-stream surveys to evaluate the trade-offs in the information content provided on fish habitat metrics.  Multi-spectral pixel colors from UAV surveys were correlated to stream depths collected during in-stream surveys to create digital elevation models (DEMs) of stream bathymetry. High resolution DEMs were also created from total station surveys in overlapping areas. Additional habitat information, such as the channel unit type and large wood were also collected during these surveys.  We were able to recreate stream bathymetry using aerial photography; however, the resolution was much lower than total station surveys and inconsistencies in lighting from shadows of vegetation and clouds added noise in depth estimates. Several other stream habitat features could also be observed in these photographs such as gravel bars, large wood, and riparian vegetation. The benefits of gaining information over large spatial extents can provide valuable data for evaluating fish habitat and when possible should be integrated with in-stream habitat assessments to provide spatial context.