The important variable of horizontal visibility within forest stands is gaining increasing attention in studies and applications involving terrestrial laser scanning (TLS), photographic measurements of forest structure, and autonomous mobility. We investigated distributions of visibility distance, open arc length, and shaded arc length in three mature forest stands. Our analysis was based (1) on tree position maps and TLS data collected in 2013 and 2019 with three different scanners, and (2) on simulated digital twins of the forest stands, constructed with two pattern-generation models incorporating commonly used indices of tree position clumping. The model simulations were found to yield values for visibility almost identical to those calculated from the corresponding tree location maps. The TLS measurements, however, were found to diverge notably from the simulations. Overall, the probability of free line of sight was found to decrease exponentially with distance to target, and the probabilities of open arc length and shaded arc length were found to decrease and increase, respectively, with distance from the observer. The TLS measurements, which are sensitive to forest understory vegetation, were found to indicate increased visibility after vegetation removal. Our chosen visibility prediction models support practical forest management, being based on common forest inventory parameters and on widely used forest structure indices.

Soil penetration resistance (Pr) measurement is important for assessing compaction and permeability; however, Pr is heavily dependent on soil moisture. Therefore, the interpretation of Pr data is significantly more reliable if moisture is measured simultaneously and in the same soil layer. In addition, reliable assessment of permeability requires consideration of both soil moisture and penetration resistance. The aim of this work was to develop a prototype of a hand-held combined device in which a volumetric moisture sensor operating on the principle of a galvanic cell is integrated into the Pr measurement cycle, allowing simultaneous measurements at different depths. The device simultaneously determined the penetration resistance acting on the cone, the measurement depth (with a laser sensor), the volumetric moisture (Cu–Zn electrode pair), and the location of the measurement site (GNSS). The moisture sensor was found to be neutral to the influence of the mineral part of the soil on moisture measurement, which in the case of other alternative measurement methods significantly affects the soil moisture measurement data. The calibration of the galvanic moisture sensor was performed under laboratory conditions (VWC 5–50%) based on a gravimetric reference. The relationship was approximately linear at lower moistures and nonlinear at higher moistures. The salinity effect test indicated that the TDR-based reference device gave a strongly overestimated moisture reading in saline soil, while the galvanic cell-based measurement remained within a realistic range compared to the gravimetric method. The results indicate that Pr measurement integrated with a galvanic sensor creates a practical prerequisite for the simultaneous collection of Pr and moisture profiles and is useful in conditions where dielectric methods are affected by salinity or minerality interference.

Soil disturbance will remarkably alter physical properties of the soil  and the recovery of the structure as well as mechanical strength recovery will take  years. Typically deforestation works, e.g. needed for the establishment of open military training areas, seriously influences soil mechanical state. Deforestation works involve processes like felling of trees, uprooting of stumps followed by levelling of ground. For the establishment of more favourable conditions for grass cover development, tree stumps and felling residues are mixed into the soil with a rotary thriller. Therefore, the final disturbed ground  has low density and high porosity resulting in low mechanical strength. On the  contrary, military training includes high intensity movement by soldiers and trafficking by vehicles. Thus, these types of activities presume stable soil conditions with a high mechanical strength. The aim of our research was to investigate soil density status of disturbed grassland with computed tomography. The soil samples were collected from the undisturbed area and from the grassland which was treated with the rotary thriller 2 years ago. The undisturbed soil samples were collected using plastic cylinders (of 10 cm diameter and 20 cm height) in 3 repetitions.  For comparison, smaller soil samples (5.3 cm diameter and 4 cm height) were obtained at 0, 5, 10, 15, 20, 30 cm depths  for determining the soil bulk density. In the  laboratory, the high resolution industrial computed tomography system Yxlon FF 35 CT was used with the larger soil samples. The soil samples were analyzed using the software Volume Graphics VGSTUDIO MAX 3.2.  Our results indicated the possibility of determination of distribution of pores in the soil and the changes in the porosity of soils depending on the soil treatment and the type.

Military training areas have to sustain the intensive usage of tracked and wheeled vehicles and the dismounted movement of soldiers. The periodic nature of training activities causes heavy loads, including a high number of loading repetitions on the soil; this makes the mechanical strength and recovery of soil a consequential issue. In many cases, the preparation of new training areas involves field preparations, e.g. earthmoving or deforestation activities that lead to serious disturbance of soil, especially its natural mechanical strength. The goal of this study was to investigate the potential methods to determine the conditions of previously disturbed military training areas. Soil measurements were carried out two years after deforestation works. Within this study, soil samples were collected and the mechanical strength of soil was determined in July and November 2020, with the aim to characterize soil conditions during dry and wet periods. Soil bulk density as well as cone penetrometer and dynamic cone penetrometer measurements were carried out.  In chemical parameters of soil, the total carbon content was measured as an indicator of uniformity by mixing organic matter in the soil surface (25 cm) layer. As the development of plant cover and especially its tight root system is very important for increasing the mechanical strength of soil, the content of plant available nutrients (P, K, Mg and Ca) was also measured. To evaluate the uniformity of blended upper soil layer, the soil was divided into 5 different layers of 5 cm thick each. The bulk density was determined for each layer. The chemical parameters of soil were determined for each layer separately and a diagram of element content in profile was created according to obtained results. This presentation will address the preliminary results of field measurements.