Modeling Vegetation Heights from High Resolution Stereo Aerial Photography: An Application for Broad-Scale Rangeland Monitoring
Jeffrey Gillan
Jason Karl
Michael Duniway
Publication Year

Vertical vegetation structure in rangeland ecosystems can be a valuable indicator for monitoring rangeland health or progress toward management objectives because of its importance for assessing riparian areas, post-fire recovery, wind erosion, and wildlife habitat. Federal land management agencies are directed to monitor and manage rangelands at landscapes scales, but traditional field methods for measuring vegetation heights are often too costly and time consuming to apply at these broad scales. Emerging remote sensing techniques (e.g., LiDAR or synthetic aperture radar) are too expensive, require specialized sensors, or are not of high enough resolution for broad-scale application. An alternative remote sensing approach is to measure vegetation heights from digital stereo aerial photographs. The purpose of this study was to test the feasibility and accuracy of estimating shrub heights from high-resolution (HR, 3-cm ground sampling distance) digital stereo-pair aerial images. Overlapping HR imagery was taken in March 2009 near Lake Mead, Nevada and 5 cm resolution digital terrain models (DTMs) were created for twenty-six 2,500 m2 test plots. We compared the heights of individual shrubs and plot averages derived from the DTMs to field measurements. Modeling success was highly variable, dependent primarily on the type of vegetation in the plot. The resolution of the imagery was too coarse to accurately capture the heights of herbaceous vegetation and fine shrub branches. However, compact shrubs were modeled very accurately. Through the use of statistically derived correction factors, though, vegetation heights from HR DTMs could be a valuable technique for broad-scale rangeland monitoring needs.

Additional Information
Jeffrey Gillan1, Jason Karl1, Michael Duniway2 --- 1USDA-ARS Jornada Experimental Range, Las Cruces, New Mexico, USA, 2Canyonlands Research Station, USGS-BRD, Moab, Utah, USA