Vibration Analyses of a Gantry Structure by Mobile Phone Digital Image Correlation and Interferometric Radar

The study presents results from applying the Real Aperture Radar interferometry technique and Digital Image Correlation through a mobile phone camera to identify static and dynamic deformations of a gantry during surveying operations on the Michelangelo’s David at the Galleria dell’Accademia di Firenze Museum in Florence. The statue has considerable size and reaches an elevation of more than seven meters on its pedestal. An ad-hoc gantry was designed and deployed, given the cramped operating area around the statue. The scanner had a stability control system that forbid surveying in instrument movements. However, considering the unicity of the survey and its rare occurrence, the previous survey had been carried out in the year 2000; verifying stability and recording deformations is a crucial task, and necessary for validation. As the gantry does not have an on-board stability sensor, and considering the hi-survey accuracy requested, a redundant, contactless, remote monitoring system of the gantry and the statue stability was chosen to guarantee the maximum freedom of movement around the David to avoid any interference during scanning operations. Thanks to the TInRAR technique, the gantry and the statue were monitored with an accuracy of 0.01 mm. At the same time, a Digital Image Correlation analysis was performed on the gantry, which can be considered a Multi-Degree-Of-Freedom (MDOF) system, to accurately calculate the vibration frequency and amplitude. A comparison between TInRAR and DIC results reported substantial accordance in detecting gantry’s oscillating frequencies; a predominant oscillation frequency of 1.33 Hz was identified on the gantry structure by TinSAR and DIC analysis.

Mine surveying technique and steel storage tank base deformation removal

Introduction. Vertical steel tanks are extensively used in oil fields to hold crude oil and other liquids. Their construction requires continuous surveying control. However, measurement procedures, data processing, and deviations and documentation correction are not universal and cannot be applied for tanks with a capacity of less than 3000 m3. Moreover, the process of correcting the detected bottom irregularities is poorly substantiated and intuitive. Research objective is to improve the as-built survey accuracy and reliability of the low-capacity steel tank bottom, substantiate the minimum height of its irregularities, increase the objectivity and productivity of measurement processing, develop an unambiguous method for time-predictable correction of bottom irregularities, and substantiate the optimal contents of its relief’s as-built scheme. Methods of research. Geometric leveling for the bottom profile survey failed to provide adequate accuracy and was therefore replaced by the method of trigonometric leveling. A method has been developed for determining the deviations of the existent tank bottom profile from the design position by means of algebraic actions with surfaces of a topographic order. The accuracy of determining the smallest height of bottom irregularities has been estimated under the tacheometric survey. A method has been proposed for controlling the correction of tank bottom irregularities based on evaluation calculations of bottom deformations by the finite element method. Research results. All the development results are exemplified by a specific production example. It was found that for a full completion of work, two iterations of tank bottom irregularities correction are enough. Methods of optimal design for the facility’s as-built schemes are presented. Conclusions. A simple, accurate, low-cost, productive, and time-predictable method of mine surveying, mathematical processing and correction of deviations in the tank bottom profile has been developed. This technique reduces the construction period and increases the operating time of the facility.

MULTI-TEMPORAL IMAGE CO-REGISTRATION OF UAV BLOCKS: A COMPARISON OF DIFFERENT APPROACHES

Traditionally, data co-registration of survey epochs in photogrammetry relied on Ground Control Points (GCP) to keep the reference system unchanged. In the last years, Unmanned Aerial Systems (UAV) are increasingly used in photogrammetric environmental monitoring. The diffusion of affordable UAV platforms equipped with GNSS (Global Navigation Satellite System) centimetre-grade receivers might reduce, but not eliminate, the need for GCP. Conversely, if GNSS-assisted orientation cannot be used or if additional ground control and reliability checks are required, alternatives to repeated GCP survey have been proposed, taking advantage of Structure from Motion (SfM) photogrammetry. In particular, co-registering different epochs image blocks together, identifying corresponding features, has been demonstrated as a viable and efficient approach. In this paper four different strategies easily implementable in a generic commercial photogrammetric software are presented and compared considering three different test sites in Italy subject to different amounts of environmental changes. The influence of the amount and distribution of inter-epoch corresponding points on the accuracy of the reconstruction is investigated. The results show that some of the tested strategies obtains very good results and can be used (although not needed) also in RTK centimetre-grade UAV surveys, leveraging the additional information coming from previous epochs survey to actually increase the survey accuracy and reliability.

Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber

Ultrasonic bat detectors are useful for research and monitoring purposes to assess occupancy and relative activity of bat communities. Environmental “clutter” such as tree boles and foliage can affect the recording quality and identification of bat echolocation calls collected using ultrasonic detectors. It can also affect the transmission of calls and recognition by bats when using acoustic lure devices to attract bats to mist-nets. Bat detectors are often placed in forests, yet automatic identification programs are trained on call libraries using echolocation passes recorded largely from open spaces. Research indicates that using clutter-recorded calls can increase classification accuracy for some bat species and decrease accuracy for others, but a detailed understanding of how clutter impacts the recording and identification of echolocation calls remains elusive. To clarify this, we experimentally investigated how two measures of clutter (i.e., total basal area and number of stems of simulated woody growth, as well as recording angle) affected the recording and classification of a synthesized echolocation signal under controlled conditions in an anechoic chamber. Recording angle (i.e., receiver position relative to emitter) significantly influenced the probability of correct classification and differed significantly for many of the call parameters measured. The probability of recording echo pulses was also a function of clutter but only for the detector angle at 0° from the emitter that could receive deflected pulses. Overall, the two clutter metrics were overshadowed by proximity and angle of the receiver to the sound source but some deviations from the synthesized call in terms of maximum, minimum, and mean frequency parameters were observed. Results from our work may aid efforts to better understand underlying environmental conditions that produce false-positive and -negative identifications for bat species of interest and how this could be used to adjust survey accuracy estimates. Our results also help pave the way for future research into the development of acoustic lure technology by exploring the effects of environmental clutter on ultrasound transmission.

SURVEY ACCURACY AND SPATIAL RESOLUTION BENCHMARK OF A CAMERA SYSTEM MOUNTED ON A FAST FLYING DRONE

Many drones are used to obtain high resolution imagery. Subsequent 3D object point derivation from images of these systems is an established technique. While rotor-craft drones are often used to capture fine, detailed structures and objects in small-scale areas fixed-wing versions are commonly used to cover larger areas even far beyond line of sight. Usually, these drones fly at much higher velocities during data acquisition and therefore the according sensor requirements are much higher.This paper presents the evaluation of a prototype camera system for fast flying fixed-wing drones. Focus of investigation is to find out if higher operating velocities, up to 100 km/h during image acquisition, has any influence on photogrammetric survey and image quality itself. It will be shown that images, obtained by the presented camera system and carrier, do not suffer from motion blur and that the overall survey accuracy is approximately 1/4 of ground sample distance.Survey accuracy analysis is carried out using standard photgrammetric procedures using signaled control- and checkpoints and verifying their conformity in image space and object space.Fundamentals of image quality will be introduced, as well asan approach to determine and evaluate motion smear of remote sensing senors (in theory and practical use case). Furthermore, it will be shown that the designed camera system mounted on a fixed-wing carrier does not suffer from motion smear.

The impact of sensors for satellite derived bathymetry within the Canadian Arctic

Canada’s coastline presents challenges for charting. Within Arctic regions, in situ surveying presents risks to surveyors, is time consuming and costly. To better meet its mandate, the Canadian Hydrographic Service (CHS) has been investigating the potential of remote sensing to complement traditional charting techniques. Much of this work has focused on evaluating the effectiveness of empirical satellite derived bathymetry (SDB) techniques within the Canadian context. With greater knowledge of applying SDB techniques within Canadian waters, CHS is now interested in understanding how characteristics of optical sensors can impact SDB results. For example, how does the availability of different optical bands improve or hinder SDB estimates? What is the impact of spatial resolution on SDB accuracy? Do commercial satellites offer advantages over freely available data? Through application of a multiple band modelling technique to WorldView-2, Pléiades, PlanetScope, SPOT, Sentinel-2, and Landsat-8 imagery obtained over Cambridge Bay, Nunavut, this paper provides insight into these questions via comparisons with in situ survey data. Result highlights in the context of these questions include the following: Similarities between sensors: Overall linear error at 90% (LE90) results for each sensor ranged from 0.88 to 1.91 m relative to in situ depths, indicating consistency in the accuracy of SDB estimates from the examined satellites. Most estimates achieved Category of Zone of Confidence level C accuracy, the suggested minimum survey accuracy level for incorporating SDB information into navigational charts. SDB coverage: Between sensors, differences in the area of the sea floor that could be measured by SDB were apparent, as were differences in the ability of each sensor to properly represent spatial bathymetry characteristics. Sensor importance: Though relationships between SDB accuracy and sensor resolution were found, significant advantages or disadvantages for particular sensors were not identified, suggesting that other factors may play a more important role for SDB image selection (e.g., sea floor visibility, sediments, waves). Findings from this work will help inform SBD planning activities for hydrographic offices and SDB researchers alike.

RECEPTORES DE SINAIS DO SISTEMA GLOBAL DE NAVEGAÇÃO POR SATÉLITE SUBMETIDOS A INTERFERÊNCIAS FÍSICAS

RECEPTORES DE SINAIS DO SISTEMA GLOBAL DE NAVEGAÇÃO POR SATÉLITE SUBMETIDOS A INTERFERÊNCIAS FÍSICAS JOÃO LUIZ JACINTHO1, GABRIEL ARAÚJO E SILVA FERRAZ2, LUCAS SANTOS SANTANA3, PATRÍCIA FERREIRA PONCIANO FERRAZ4 1 Instituto Federal do Norte de Minas Gerais - IFNMG, Campus Araçuaí BR 367, km 278, s/n - Zona Rural, 39600-000, Araçuaí - MG, Brasil. [email protected]. 2 Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. 3Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. 4 Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. RESUMO: Incertezas são encontradas em trabalhos com receptores do Sistemas Global de Navegação por Satélite GNSS. Diante disso, objetivou-se com este estudo investigar a influência de obstáculos físicos nos erros de acurácia e precisão em levantamentos com receptores GNSS e suas aplicações agrícolas. Foram implantados quatros pontos de controle rastreados no modo estático (base) e oito pontos de estudos rastreados no modo cinemático em tempo real (RTK) e Estático Rápido (ER), utilizando um par de receptores GNSS e um par de receptores GNSS-RTK. Os níveis de acurácia e precisão foram avaliados em oito pontos obtidos por rastreios do tipo ER e RTK. Combinados com quatro bases fixas, alocados de três formas: mínima, média e alta interferência física. Pontos provenientes do levantamento RTK, apresentaram diferenças na ordem de milímetros a centímetros, quando comparados às coordenadas obtidas do levantamento (ER). Para os níveis de obstrução, a mínima interferência apresentou erro dentro dos limites estipulados pelo equipamento, a máxima interferência apresentou menor acurácia. O efeito do multipercurso do sinal foi o fator mais determinante para a redução da acurácia das coordenadas dos pontos. Recomenda-se a aplicação do levantamento RTK para trabalhos onde a precisão das coordenadas seja mais relevante que a acurácia. Palavras-chaves: Geodésia, levantamento planialtimétrico, acurácia, precisão. GLOBAL SATELLITE NAVIGATION SYSTEM RECEIVERS SUBMITTED TO PHYSICAL INTERFERENCES ABSTRACT: Uncertainties are found in works with Global Navigation Satellite System receivers (GNSS). Therefore, this study aimed to investigate influence physical obstacles on accuracy and precision errors in surveys with GNSS receivers and their agricultural applications. Four control points tracked in static (base) mode and eight study points tracked in a kinematic mode in real-time (RTK) and Fast Static (ER) were implemented, using a pair of GNSS receivers and pair of GNSS-RTK receivers. Accuracy levels and precision were evaluated at eight points obtained by ER and RTK, combined with four fixed bases, allocated in three ways: minimal, medium and high physical interference. RTK survey points showed differences order millimeters to centimeters when compared to the survey (ER) coordinates. The obstruction levels, interference minimum, had an error within limits stipulated by equipment, interference maximum showed low accuracy. RTK survey is recommended for jobs where the coordinate precision is more relevant than accuracy. Keywords: Geodesy, planialtimetric survey, accuracy, precision.

The Accuracy and Value of Voter Validation in National Surveys: Insights from Longitudinal and Cross-Sectional Studies

Ansolabehere and Hersh and others have examined the reported voting behavior of survey respondents using a variety of validation methods, including matching with national voter files provided by outside vendors. This analysis provides the first examination of a thirty-year national longitudinal study and compares the insights obtained from this longitudinal analysis to two 2016 national cross-sectional studies of voting behavior using structural equation modeling. We find that respondents of the longitudinal study overreport at lower rates than respondents in our 2016 samples, and the traditional predictors of overreporting such as political interest, engagement, and partisanship predict overreporting among respondents in both our longitudinal and 2016 short-term panel studies, but our longitudinal data include novel predictors of overreporting such as parent socialization factors. We conclude with a discussion of the phenomenon of overreporting in surveys and how survey accuracy becomes increasingly important for both the public and policymakers in an era of decreasing trust in institutions and expertise.

Compensation Method for Diurnal Variation in Three-Component Magnetic Survey

Considering that diurnal variation interferes with three-component magnetic surveys, which inevitably affects survey accuracy, exploring an interference compensation method of high-precision is particularly desirable. In this paper, a compensation method for diurnal variation is proposed, the procedure of which involves calibrating the magnetometer error and the misalignment error between magnetometer and non-magnetic theodolite. Meanwhile, the theodolite is used to adjust the attitude of the magnetometer to unify the observed diurnal variation into the geographic coordinate system. Thereafter, the feasibility and validity of the proposed method were verified by field experiments. The experimental results show that the average error of each component between the observed value of the proposed method and that of Changchun Geomagnetic station is less than 1.2 nT, which indicates that the proposed method achieves high observation accuracy. The proposed method can make up for the deficiency that traditional methods cannot meet the requirements of high accuracy diurnal variation compensation. With this method, it is possible for us to set up temporary diurnal variation observation station in areas with complex topography and harsh environment to assist aeromagnetic three-component survey.