Variation of structured laser beam pattern and optimization for an alignment reference line creation.

The alignment of particle accelerators demands a dedicated measurement system based on a straight-line reference. This straight line can be provided by a laser beam. The alignment then involves accurately measuring the offset of accelerator components with respect to this light path. In order to be efficient, the laser beam needs to serve as a stable and straight reference for distances of several hundreds of meters. The attainable accuracy depends, among other parameters, on the laser spot size, which should ideally change very little over the distances at which the alignment system needs to operate. Due to the significant divergence of Gaussian laser beams, we propose using a structured laser beam (SLB) for alignment. Its transversal intensity profile is similar to a Bessel beam and consists of an intense inner core (IC) and concentric rings. The divergence of the IC, i.e., the growth of its size with distance, can be limited to 10µrad using a favorable generator configuration. Thus an SLB may be suitable as a straight-line reference for long-distance alignment applications. However, the SLB is distorted if obstructions cover parts of the outermost ring (OR) of the beam within, which should therefore also be small. In this paper, we investigate the relationship between the size of the IC and OR depending on the design parameters of the SLB generator. We use numerical simulations and experiments with different generators over distances up to 50 m to analyze the transversal intensity profile and wavefronts of different SLBs. The results indicate the general suitability of an SLB as a reference line for long-distance alignment but also expose tradeoffs between small IC and small OR. The findings outlined in the paper help to describe the optimal SLB parameters for given conditions.

Assessment of the Possibility of Using Unmanned Aerial Vehicles (UAVs) for the Documentation of Hiking Trails in Alpine Areas.

The research described in this paper deals with the documentation of hiking trails in alpine areas. The study presents a novel research topic, applying up-to-date survey techniques and top quality equipment with practical applications in nature conservation. The research presents the initial part of the process-capturing imagery, photogrammetric processing, quality checking, and a discussion on possibilities of the further data analysis. The research described in this article was conducted in the Tatra National Park (TNP) in Poland, which is considered as one of the most-visited national parks in Europe. The exceptional popularity of this place is responsible for intensification of morphogenetic processes, resulting in the development of numerous forms of erosion. This article presents the outcomes of research, whose purpose was to verify the usability of UAVs to check the condition of hiking trails in alpine areas. An octocopter equipped with a non-metric camera was used for measurements. Unlike traditional methods of measuring landscape features, such a solution facilitates acquisition of quasi-continuous data that has uniform resolution throughout the study area and high spatial accuracy. It is also a relatively cheap technology, which is its main advantage over equally popular laser scanning. The paper presents the complete methodology of data acquisition in harsh conditions and demanding locations of hiking trails on steep Tatra slopes. The paper also describes stages that lead to the elaboration of basic photogrammetric products relying on structure from motion (SfM) technology and evaluates the accuracy of the materials obtained. Finally, it shows the applicability of the prepared products to the evaluation of the spatial reach and intensity of erosion along hiking trails, and to the study of plant succession or tree stand condition in the area located next to hiking trails.