Abstract. The emergence of single-frequency, navigation-type Global Navigation Satellite System receivers capable to provide carrier phase data [the so-called high sensitivity (HS) carrier phase positioning] has been steadily growing over the recent years. The main purpose of this study is to metrologically evaluate two low-cost, HS receivers, namely the u-blox LEA-6T and NEO-7P, in control surveying specifications. The evaluation was carried out within a published framework of standards and associated guidelines that are consistent with standards from the International Standards Organisation. The survey results were obtained from sufficient independent testing and proof and achieved an accuracy classification of '1 cm' at 95% confidence level. This indicates that the particular type of receiver used with geodetic antennas can provide positioning results for general purpose control surveying applications that are comparable to using geodetic receivers and with a significantly lower cost.

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Abstract. Narrow space surveying and mapping is of high importance for many applications, with the demand for digital 3D models in a low-cost and relatively fast way growing rapidly. This paper examines SLAM-based and image-based mapping systems for indoor mapping and focuses on the comparison of the 3D point clouds acquired from two commercial mapping systems, Leica BLK2GO and Matterport Pro2 3D (MC250). Issues that are addressed include the effect of the mapping trajectory on the produced mapping result, and the amount of mapping propagation error in narrow space surveying. The two systems are experimentally compared against both an ideal geometric target facility and in an example environment of a narrow corridor. Finally, results are given with derived metrics that can be possibly extended to several real applications.

Dynamic characterization and Structural Health Monitoring (SHM) are crucial tools, of increasing demand, for reliable operation and predictive maintenance of large infrastructures, as the percentage of critically ageing infrastructures is growing steadily. We present a minimally invasive and synchronous fiber optic monitoring system for SHM, based on Phase-Optical Time-Domain Reflectometry (Phase-OTDR), and we assess its applicability and performance on a modular Bailey-type bridge of 1 : 2.5 scale. Phase-OTDR systems, along with other fiberoptic-distributed techniques have proven their capabilities in long-range SHM applications, although their complexity and high cost limits drastically their applicability and SHM market penetration. Here, we propose the use of a prototype Phase-OTDR system, featuring customized interrogation instrumentation with a balanced trade-off between performance and cost. Its experimental validation is achieved by comparison with well-established commercial monitoring systems, such as Ground-Based Radar Interferometer (GBRI), laser tracker, and multipoint optical Fiber Bragg Gratings (FBGs), in various excitation conditions and structure-damage scenarios, easily implementable in the model bridge. Finite-element modelling (FEM) and simulations were employed to study the bridge behaviour and provide a reference and comparison framework for the experimental characterization. The Phase-OTDR system successfully detected the structural behaviour in an efficient distributed manner, demonstrating comparable performance to commercial point sensor systems, thus demonstrating its application potential.

This paper presents the dynamic testing of a roadway, single-span, cable-stayed bridge for a sequence of static load and ambient vibration monitoring scenarios. Deck movements were captured along both sideways of the bridge using a Digital Image Correlation (DIC) and a Ground-based Microwave Interfererometer (GBMI) system. Cable vibrations were measured at a single point location on each of the six cables using the GBMI technique.Dynamic testing involves three types of analyses; firstly, vibration analysis and modal parameter estimation (i. e., natural frequencies and modal shapes) of the deck using the combined DIC and GBMI measurements. Secondly, dynamic testing of the cables is performed through vibration analysis and experimental computation of their tension forces. Thirdly, the mechanism of cable-deck dynamic interaction is studied through their Power Spectra Density (PSD) and the Short Time Fourier Transform (STFT) analyses. Thereby, the global (deck and cable) and local (either deck or cable) bridge modes are identified, serving a concrete benchmark of the current state of the bridge for studying the evolution of its structural performance in the future. The level of synergy and complementarity between the GBMI and DIC techniques for bridge monitoring is also examined and assessed.