A Methodological Intercomparison of Topographic and Aerial Photographic Habitat Survey Techniques

Numerous field and analytical methods exist to assist in the quantification of the quantity and quality of in-stream habitat for salmonids.  These methods range from field sketches or ‘tape and stick’ ground-based surveys, through to spatially explicit topographic and aerial photographic surveys from a mix of ground-based and remotely sensed airborne platforms.  Although some investigators have assessed the quality of specific individual survey methods, the inter-comparison of competing techniques across a diverse range of habitat conditions (wadeable headwater channels to non-wadeable mainstem channels) has not yet been elucidated. In this study, we seek to quantify relative quality (i.e. accuracy, precision, extent) of habitat metrics and inventories derived from different ground-based, boat-based and remotely sensed surveys of varying degrees of sophistication, as well as enumerate the effort and cost in completing the surveys.  Over the summer of 2010, seven sample reaches of varying habitat complexity were surveyed in the Lemhi River Basin, Idaho, USA.  Complete topographic/bathymetric surveys were attempted at each site using separate rtkGPS, total station, ground-based LiDaR, traditional airborne LiDaR, and imagery-based spectral correlation methods. Separate, georectified aerial imagery surveys were acquired using a tethered blimp, a drone UAV, and a traditional fixed-wing aircraft.  Preliminary results from the surveys highlight that no single technique outperforms the others across the full range of conditions where stream habitat surveys are needed. The results are helpful for understanding the strengths and weaknesses of each approach in specific conditions, and how a hybrid of data acquisition methods can be used to build a more complete quantification of salmonid habitat conditions in rivers of the Columbia River Basin.