Unmanned Aerial Vehicles for Rangeland Mapping and Monitoring: a Comparison of Two Systems

Aerial photography from unmanned aerial vehicles (UAVs) bridges the gap between ground-based observations and remotely sensed imagery from aerial and satellite platforms. UAVs can be deployed quickly and repeatedly, are less costly and safer than piloted aircraft, and can obtain very high-resolution imagery. At the Jornada Experimental Range in New Mexico, ongoing research is aimed at determining the utility of UAVs for rangeland mapping, assessment and monitoring. Digital images of arid rangelands were acquired with two UAVs that differed in size/weight, payload capacity, flight duration, GPS guidance capability and cost. The first system was a modified model airplane equipped with GPS and able to fly along preloaded waypoints and acquire images with a digital camera. The second UAV was a BAT 3 (MLB Systems) with fully autonomous flight capability and equipped with color video and digital cameras. Both units provide a data file containing GPS and elevation for each image, but the BAT also records roll, pitch and heading data. Both systems acquired high quality, high-resolution images of approximately 5 cm ground resolution (at 150 m flying height). Because the images have a small footprint (152 m x 114 m), mosaicking is required for further image analysis. Inclusion of camera calibration parameters (lens distortion, focal length, principal point) greatly increased the accuracy of the aero triangulation process and the resulting orthophotos. Due to the greater stability of the BAT and its longer flight range, the BAT imagery is better suited for analysis of larger areas than the imagery from the model airplane. However, the model airplane offers comparable image resolution and a cost effective alternative to the larger and more expensive UAV systems. Details of both systems, image acquisition and image processing results are discussed and compared.