Accuracy and optimal altitude for physical habitat assessment (PHA) of stream environments using unmanned aerial vehicles (UAV)

Abstract

Physical Habitat Assessments (PHA) are useful to characterize and monitor stream and river habitat conditions, but can be costly and time-consuming. Alternative methods for data collection are getting attention, such as Unmanned Aerial Vehicles (UAV). The objective of this work was to evaluate the accuracy of UAV-based remote sensing techniques relative to ground-based PHA measurements, and to determine the influence of flight altitude on those accuracies. A UAV quadcopter equipped with an RGB camera was flown at the altitudes of 30.5 m, 61.0 m, 91.5 m and 122.0 m, and the metrics wetted width (Ww), bankfull width (Wbf) and distance to water (Dw) were compared to field PHA. The UAV-PHA method generated similar values to observed PHA values, but underestimated distance to water, and overestimated wetted width. Bankfull width provided the largest RMSE (25–28%). No systematic error patterns were observed considering the different flight altitudes, and results indicated that all flight altitudes investigated can be reliably used for PHA measurements. However, UAV flight at 61 m provided the most accurate results (CI = 0.05) considering all metrics. All UAV parameters over all altitudes showed significant correlation with observed PHA data, validating the use of UAV-based remote sensing for PHA.