Photogrammetric estimation of wheel rut dimensions and soil compaction after increasing numbers of forwarder passes

Compaction and rutting on forest soils are consequences of harvesting operations. The traditional methods used to investigate these consequences are time consuming and unable to represent the entire longitudinal profile for a forest trail. New methods based on photogrammetry have been developed. The overall objective was to compare photogrammetry and traditional methods (e.g. cone penetrometer, manual rut depth measurements, bulk density and porosity) used for the evaluation of soil compaction and rutting (i.e. depth and rut volume) after multiple passes of a loaded forwarder using two different tyre pressure levels. The comparison of photogrammetric versus manually measured profiles resulted in R2 0.93. Both tyre inflation pressure and number of passes had effect on soil disturbance. The rut volumes on 100m long trails after 60 passes were 8.48 and 5.74m(3) for tire pressures of 300 and 150kPa, respectively. Increased rut volume correlated positively with increased soil compaction and decreased soil porosity. Structure-from-motion photogrammetry is an accurate method for informing the creation of high-resolution digital evolution models and for the morphological description of forest soil disturbance after forest logging. However, a problem with photogrammetry is object reflection (grass, logging residues and water) that in some cases influence the accuracy of the method.