Extreme close-range photogrammetry was used to monitor erosion on five plots in areas of high off-highway vehicle (OHV) use on Bureau of Land Management administered rangeland near Montrose, Colorado. The technique developed enables precise measurements to be made from photographs taken with hand held or tripod mounted high-quality digital cameras.

Plots were established on five sites exhibiting impacts of OHV use. A series of stereoscopic photographs were taken of the subject areas in 2005 concurrently with oblique-orientation photographs to collect digital photo data and facilitate stereoscopic viewing of the subject area. Adam Tech 3DM software was used to recreate, in three dimensions, the geometry of the soil surface for the purpose of compiling data on it. The software creates a digital terrain model that consists of a closely spaced grid of thousands of x, y, z data points. The sites were revisited in 2006, for the purpose of monitoring surface elevation change.

Ten unique, highly detailed 3D surface data sets were produced by the processing with the 3DM Analyst Suite. The estimated vertical accuracy of this data is between 0.1 and 1.0 centimeters. The ten (two years for each of five plots) 3D digital terrain datasets were analyzed in ArcGIS using ArcMap and ArcScene. This process included creating a tin surface from the 3D data sets, converting the tin to a grid, and generating a hillshade from the grid (Figure 2). The grids were created with a resolution of 3 centimeters. Cut and fill and surface subtractions were conducted utilizing the surface grids. Based on the results of the analysis of the surfaces all five sample plots exhibited high levels of loss and gain (or movement) of soil.