Evaluation of Bare Ground on Rangelands Using Unmanned Aerial Vehicles: A Case Study

Attention is currently being given to methods that assess the ecological condition of rangelands throughout the United States. Bare ground is being considered by a number of agencies and resource specialists as a key indicator that can be evaluated over a broad area. Traditional methods of measuring bare ground rely on field technicians collecting data along a line transect or from a plot. Unmanned aerial vehicles (UAVs) provide an alternative to collecting field data, can monitor a large area in a relatively short period of time, and in many cases, can enhance the safety and time required to collect data. In this study, both fixed-wing and helicopter UAVs were used to measure bare ground in a sagebrush steppe ecosystem. The data were collected with digital imagery and read using the image analysis software, Sample-Point. The approach was tested over seven different plots and compared against traditional field methods to evaluate accuracy for assessing bare ground. The field plots were located on the Idaho National Laboratory (INL) site west of Idaho Falls, Idaho, in locations where there is very little disturbance by humans and the area is grazed only by wildlife. Mean fixed-wing and helicopter UAV bare ground values were within 1% of field estimates. This study shows that if a high degree of detail and data accuracy is desired, a helicopter UAV may be a good platform. If the data collection objective is to assess broad-scale landscape level changes, the collection of imagery with a fixed-wing system is probably more appropriate.