L-alueen taajuuspyyhkäisevän radiometrin suunnittelu ja toteutus

L-band (1-2 GHz) radiometry has been an ongoing research topic in the Department of Radio Science and Engineering for a number of years. In addition to remote sensing and radioastronomy applications, a radiometer can be used for detecting unwanted radio emissions in a protected frequency band. A frequency scanning radiometer (FIRaL) for detecting radio interference at the frequency interval of 1920 – 1980 MHz is designed and realised in this Licentiate thesis work. The aforementioned frequency band is reserved for mobile communication applications. The theory of radiometry is presented to the necessary extent in order to facilitate the FIRaL radiometer design. The design of the receiver and local oscillator electronics and pyramidal horn antenna is presented. Radiometer performance is studied by measuring the relevant device parameters in laboratory conditions. The feasibility of the radiometer to perform real-world interference surveys is tested by on-site measurements. The realised radiometer receiver input noise temperature is 661 ± 58 K or better. The radiometer is deemed suitable for interference measurements. The preliminary on-site measurements suggests that further measurements are feasible in order to study the extent of radio emissions in the 1920 – 1980 MHz mobile communications band.Radiotieteen ja –tekniikan laitoksella on jo useita vuosia tutkittu L-alueen (1-2 GHz) radiometriasovelluksia. Kaukokartoituksen ja radioastronomian ohella radiometreillä voidaan tutkia radiotaajuisia häiriöitä suojatuilla taajuusalueilla. Tässä työssä on suunniteltu ja toteutettu L-alueen taajuuspyyhkäisevä radiometri (FIRaL) 1920-1980 MHz:in taajuusalueelta mahdollisesti löytyvien radiotaajuisten häiriöiden tutkimiseen. Edellä mainittu taajuuskaista on varattu matkaviestintäsovellusten käyttöön. Radiometria esitellään FIRaL radiometrin suunnittelun taustatiedoksi tarvittavalla laajuudella. Vastaanottimen ja paikallisoskillaattorin elektroniikan ja pyramiditorviantennin suunnittelu esitellään. Radiometrin suorituskykyä tutkitaan mittaamalla kyseisen laitteen parametrit laboratorio-olosuhteissa. Radiometrin soveltuvuus käytännön häiriömittauksiin testataan tekemällä mittauksia tyypillisessä matkaviestintätukiaseman sijaintipaikassa. Rakennetun radiometrin kohinalämpötila on maksimissaan 661 ± 58 K. Radiometri todetaan käyttökelpoiseksi häiriömittauksiin. Alustavista mittauksista löytyi todennäköisiä häiriölähteitä 1920 – 1980 MHz matkaviestintäkaistalta ja lisätutkimukset häiriöiden laajempaan kartoitukseen ovat perusteltuja

Modern empirical and modelling study approaches in fluvial geomorphology to elucidate sub-bend-scale meander dynamics

Major developments in theory and modelling techniques have taken place within the past couple of decades in the field of the fluvial geomorphology. In this review, we examine the state-of-the-art empirical and modelling approaches and discuss their potential benefits and shortcomings in deepening understanding of the sub-bend-scale fluvial geomorphology of meander bends. Meandering rivers represent very complex 3D flow and sedimentary processes. We focus on high-resolution techniques which have improved the spatial and temporal resolution of the data and thereby enabled investigation of processes, which have been thus far beyond the capacity of the measurement techniques. This review covers the measurement techniques applied in the field and in laboratory circumstances as well as the close-range remote sensing techniques and computational approaches. We discuss the key research questions in fluvial geomorphology of meander bends and demonstrate how the contemporary approaches have been and could be applied to solve these questions.</jats:p

Performance Assessment of Reference Modelling Methods for Defect Evaluation in Asphalt Concrete

The deterioration of road conditions and increasing repair deficits pose challenges for the maintenance of reliable road infrastructure, and thus threaten, for example, safety and the fluent flow of traffic. Improved and more efficient procedures for maintenance are required, and these require improved knowledge of road conditions, i.e., improved data. Three-dimensional mapping presents possibilities for large-scale collection of data on road surfaces and automatic evaluation of maintenance needs. However, the development and, specifically, evaluation of large-scale mobile methods requires reliable references. To evaluate possibilities for close-range, static, high-resolution, three-dimensional measurement of road surfaces for reference use, three measurement methods and five instrumentations are investigated: terrestrial laser scanning (TLS, Leica RTC360), photogrammetry using high-resolution professional-grade cameras (Nikon D800 and D810E), photogrammetry using an industrial camera (FLIR Grasshopper GS3-U3-120S6C-C), and structured-light handheld scanners Artec Leo and Faro Freestyle. High-resolution photogrammetry is established as reference based on laboratory measurements and point density. The instrumentations are compared against one another using cross-sections, point-point distances, and ability to obtain key metrics of defects, and a qualitative assessment of the processing procedures for each is carried out. It is found that photogrammetric models provide the highest resolutions (10-50 million points per m2) and photogrammetric and TLS approaches perform robustly in precision with consistent sub-millimeter offsets relative to one another, while handheld scanners perform relatively inconsistently. A discussion on the practical implications of using each of the examined instrumentations is presented

Auditing an urban park deck with 3D geovisualization—A comparison of in-situ and VR walk-along interviews

Virtual reality-based urban audit methods are gaining increasing attention; however, most virtual urban audit studies have focused on panoramic views. The 3D city model-based geovisualizations have remained until now rather unexplored in user studies for urban audits and for communicative urban planning. We explored the feasibility of a 3D geovisualization-based urban audit in virtual reality (VR) for assessing the perceived quality of an urban park deck in Helsinki, Finland. For this purpose, we created a photorealistic and geometrically accurate 3D model (Bryga 3D) based on photogrammetric and laser scanning data. Bryga 3D was implemented on a game engine to be viewed with a head-mounted VR display. Bryga 3D's ability to convey information in a subjective urban audit, that is, subjectively perceived affordances of a park deck, was tested in a walk-along interview study comparing auditing in situ and via the VR method. A comparison of the results with in-situ (n = 13) and VR interviews (n = 21) show that the perception of several tangible elements, such as spatial division, landforms, paths, and chairs when using Bryga VR was similar to when performed in situ. Perception of vegetation was weaker in VR in terms of its detailed quality, which somewhat affected the presented development ideas and assessment of the seasonal context. Also, weaker perception of the surroundings and city context affected the results in VR. However, considering that Bryga 3D presents an example of a highly automated 3D city modeling process conducted with minimal manual work, its results are encouraging for future attempts to advance such realizations for the purposes of communicative urban planning. 3D geovisualization-based virtual audits could be used when urban green space audits are not possible or when they are demanding to implement in situ.</p

Area-Based Approach for Mapping and Monitoring Riverine Vegetation Using Mobile Laser Scanning

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Advances in Forest Inventory Using Airborne Laser Scanning

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Airborne laser scanning outperforms the alternative 3D techniques in capturing variation in tree height and forest density in southern boreal forests.

ArticleBaltic Forestry. 24(2): 268-277. (2018)journal articl

Airborne Laser Scanning Outperforms the Alternative 3D Techniques in Capturing Variation in Tree Height and Forest Density in Southern Boreal Forests

The objective of this study is to better understand the relationship between forest structure and point cloud features generated from certain airborne and space borne sensors. Point cloud features derived from airborne laser scanning (ALS), aerial imagery (AI), WorldView-2 imagery (WV2), TerraSAR-X, and Tandem-X (TDX) data were classified as features characterizing forest height and density as well as variation in tree height. Correlations between these features and field-measured attributes describing forest height, density and tree height variation were investigated at plot scale. From the field-measured attributes, basal area (G) and the number of trees per unit area (N) were used as forest density indicators whereas maximum tree height (H-max) and standard deviation in tree height (H-std) were used as indicators for forest height and tree height variation, respectively. In the analyses, field observations from 91 sample plots (32 m x 32 m) located in southern Finland were used. Even though ALS was found to be the most accurate data source in characterizing forest structure, AI, WV2, and TDX were also capable of characterizing forest height at plot scale with correlation coefficients stronger than 0.85. However, ALS was the only data source capable of providing separate features for characterizing also the variation in tree height and forest density. Features related to forest height, generated from the other data sources besides ALS, also provided strongest correlation with the forest density attributes and variation in tree height, in addition to H-max. Due to these more diverse characterization capabilities, forest structural attributes can be predicted more accurately by using ALS, also in the areas where the relation between the attributes of interest is not solely dependent on forest height, compared to the other investigated 3D remote sensing data sources.Peer reviewe