Off-the-shelf laser scanning and close-range digital photogrammetry for measuring agricultural soils microrelief

Small-scale roughness on bare agricultural soils deter-mines very important properties such as infiltration, runoff or soil erosion. In this work, a method based on photogrammetric tools has been developed for the generation of automatic digital elevation models (DEMs) in agricultural soils, and is compared with a method based on very accurate off-the-shelf three-dimensional (3D) laser scanners. High resolution and accurate DEMs are generated by both of these non-contact techniques on two agricultural field plots of about 0.2 m(2): (i) untilled and smooth soil, and (ii) very cloddy tilled surface. Furthermore, classical microrelief parameters such as Random Roughness and Maximum Depressional Storage are computed from grid DEMs obtained by laser scanning and close-range photogrammetry. Both techniques are compared on agricultural soils in terms of data acquisition and analysis performance, resolution, accuracy, and capability of representing microrelief and for computing microrelief parameters. Both the techniques tested have proved able to generate, under ideal conditions, DEMs with high accuracy (standard deviations of the residuals were 0.121 mm and 0.467 mm for laser and photogrammetry, respectively) and resolution (about 0.4 mm for laser scanning and 1 mm for the photogrammetric method). It is also worth noting that soil DEMs can be generated by both methods in less than 2 h, using devices in field assays that are not too expensive. Laser scanning produces a far more detailed surface allowing it to reproduce smaller aggregates than the photogrammetric method. On the other hand, data acquisition is faster with digital photogrammetry. The worse performance with either method happens when they are used on a rougher type of soil. Regarding the proposed non-contact methodologies, field soil microrelief can be attained in a fast, accurate, and economic way. In addition, the microrelief parameters computed from agricultural soil grid DEMs by laser scanning and photogrammetry show quite similar values. (C) 2009 IAgrE. Published by Elsevier Ltd. All rights reserved.