Advancements in three-dimensional (3D) digital surface scanning have opened up the possibility of capturing soil morphological information from irregular objects in high resolution. One of these advancements has been the development of a multistripe laser triangulation (MLT) technique that sweeps a series of laser stripes across a surface, while a camera offset from the laser source monitors the deformation and intensity of the reflected laser stripes. MLT scanning can be used to describe soil architecture (i.e., soil structure and porosity) from soil surfaces and soil specimens. The technique allows for the geometry of both small (<1 cm) and large (several meters) objects to be digitally captured in fine detail. In this paper, we provide examples of how MLT scanning has been applied to 3D soil specimens including the determination of bulk density from clods, the quantification of ped geometries, and the development of morphometrics from casted bio-pores. Examples of soil surface application of MLT scanning include the quantification of soil structure and interpedal pores from the field (excavation walls) and quantification of volume changes and crack formation in the laboratory (soil cores). When combined with other digital morphometric tools such as computed tomography, 3D laser scanning has the potential to quantify the architecture of soils across scales ranging from submicrometers to meters.

Core Ideas Soil structure quantified in the field using a 3D laser scanning technique (MLT). MLT data and coefficient of linear extensibility combined into a structure metric. Soil water contents recorded at four depths in a field lysimeter and used in HYDRUS‐1D. Saturated conductivity (Ks) estimated with a Markov chain Monte Carlo approach. New metric better correlated to Ks in horizons with strong soil structure. Soil structure affects saturated hydraulic conductivity (Ks) by creating highly conductive macropores that preferentially transmit soil water. In this study, we explored the relationship between Ks and macropores in an Oxyaquic Vertic Argiudoll in northeastern Kansas. Macropores were quantified from an excavation wall using multistripe laser triangulation (MLT) scanning. Soil water contents were measured at four depths within a soil lysimeter installed within 2 m of the MLT‐scanned soil profile and adjacent to an Ameriflux tower monitoring precipitation, air temperature, and solar radiation. Selected hydraulic properties of soil horizons within the lysimeter were optimized to water content data using a Markov chain Monte Carlo technique in combination with the mobile–immobile water (MIM) model in HYDRUS‐1D. Estimates of Ks varied between 4198 cm d−1 in the A horizon and 0.6 cm d−1 in a 2Btss2 horizon with strongly expressed wedge structure. Approximately 87% of the variation in Ks was explained by the geometric mean of the widths of pores quantified with the MLT technique and modified by the coefficient of linear extensibility (COLE). The use of the COLE allows the widths of the macropores obtained under dry conditions to be approximated at saturation. Two models that predict Ks from either texture or water retention data resulted in Ks estimates that were similar to each other but significantly lower than Ks values predicted with MIM in horizons where structural pores dominate water flow. This technique shows a great deal of promise in better understanding and predicting the relationship of soil structure to water flow.

Soil structure is a fundamental property referring to the morphology of soil aggregates and the network of void spaces between them. Structure affects many pedogenic, hydrological, and other ecosystem service processes. While its importance is generally recognized, the tortuous nature of soil structure and its variable size and expression make this property difficult to quantify, especially at the pit scale. The absence of quantitative soil structure metrics also inhibits the ability to accurately model water flux. This research explores the application of multistripe laser triangulation (MLT) scanning to a soil profile in the field. MLT scan data were analyzed for their ability to quantitatively characterize soil structure. The study site was located near Lawrence, KS in a Grundy soil series with vertic properties, where soil moisture sensors were installed in a lysimeter next to an exposed profile. Several logistical problems concerning MLT field operations and data processing are addressed in this work including: ambient light, MLT scanner positioning in relation to the soil surface, and post-processing procedures for the resulting data. MLT scans capture the profile surface along with areas of missing data, termed surface scan gaps (SSGs), which represent preferential flow paths (PFPs) actually observed in the soil. Metrics describing SSGs were first studied to determine whether the digital data could be related to conditions observed in the field. These metrics were then examined in relation to soil hydraulic parameters, especially saturated hydraulic conductivity (Ks) and water retention curve (WRC) parameters. Soil moisture data collected at the lysimeter, in conjunction with atmospheric data from an adjacent tower, were used as inputs for Hydrus 1-D to predict, then separately to verify hydraulic parameters that were obtained using quantitative soil structure metrics. Several close relationships were identified with WRC parameters such as α and n, as well as relationships with Ks. These connections, enabled by quantification of soil structure as a

Soil structure is fundamental for understanding pedogenic, hydrological, and environmental processes, and its quantitative characterization is essential for advancing our understanding of soils. Despite this importance, structure quantification at scales relevant to field-based investigations has remained elusive. In this study, multistripe laser triangulation (MLT) scanning was investigated as a method for quantifying soil structure from excavation walls. An exposed soil profile in a Grundy soil series (fine, smectitic, mesic, Oxyaquic Vertic Argiudoll) was scanned using a commercially available MLT scanner. The field of view (FOV) for each scan overlapped adjacent FOVs in the vertical and horizontal directions. Data of interest from the MLT scans were areas where laser stripes were undetected by the scanner. These surface scan gaps (SSGs) outline structural units. We discovered that the angle between the scanner and excavation wall produces significant differences in the resulting data. Observed SSGs best represented structure outlines on the left side of the scan data FOVs. Several metrics describing SSG shape, size, and orientation were produced. Surface scan gap density, SSG fraction, relative surface area, and average unit size (i.e., size of areas outlined by SSGs) were related to soil structure described in the field. Average unit size compared well to the size classes from a traditional morphological description, and SSG orientation corresponded to structure type. Multistripe laser triangulation scanning holds potential for quantitative characterization of soil structure with implications for water flux modeling and advancing understanding of pedological and hydrological processes.