1,721,081 research outputs found
THIMRAN: A MATLAB toolbox for thermal image processing aimed at damage recognition in large bodies
No full textTHIMRAN (THermal Images Mosaicking, Registration and ANalysis) is a new MATLAB toolbox proposed for processing data provided by infrared thermography (IRT). The toolbox is able to perform a contactless recognition of damage of a large body like a masonry/concrete wall or a rock cliff, leading to useful information for health state evaluation and/or hazard assessment. In an IRT measurement session, series of thermal images are acquired throughout one or more heating/cooling diurnal cycles. The proposed approach relies on evaluation of the time history of the thermal contrast related to one or more thermal transients. This is an extension to large bodies of a method currently used in laboratory non-destructive testing. The toolbox contains all the necessary functions for a complete IRT-based evaluation of a large body: (i) preliminary image processing (mosaicking, or stitching, and registration); (ii) computation of thermal contrast for each image; (iii) damage recognition by means of pixel-by-pixel comparison of thermal images registered into the same reference frame. The toolbox is available as Supplemental data of this paper. The results of its application of to two case studies, i.e. a leaning bell tower and a rock cliff, are also described
Improving strain rate estimation from velocity data of non-permanent GPS stations: The central apennine study case (Italy)
No full textAn efficient procedure is proposed to define realistic lower limits of velocity errors of a non-permanent GPS station (NPS), i. e., a station where the antenna is installed and operates for short time periods, typically 10-20 days per year. Moreover, the proposed method is aimed at being independent of standard GPS data processing. The key is to subsample appropriately the coordinate time series of several continuous GPS stations situated nearby or inside the considered NPS network, in order to simulate the NPS behavior and to estimate the velocity errors associated with the subsampling procedure. The obtained data are used as lower limits to accept or correct the error estimates provided by standard data processing. The proposed approach is applied to data from the dense, non-permanent network in the Central Apennine of Italy based on a sequence of solutions for the overlapping time spans 1999-2003, 1999-2004, 1999-2005 and 1999-2007. Both the original and error-corrected velocity patterns are used to compute the strain rate fields. The comparison between the corresponding results reveals large differences that could lead to divergent interpretations about the kinematics of the study area. © 2009 Springer-Verlag
Long-term performance of an irregular shaped borehole heat exchanger system: Analysis of real pattern and regular grid approximation
No full textA reliable evaluation of long-term performance of a heat pump coupled with a borehole heat exchanger (BHE) field is necessary to verify the stability of its heat exchange capability over the time. The BHE field pattern is often assumed to be regular (e.g., rectangular, L-shaped, T-shaped, etc.), or is assumed to be adequately approximated by one of these shapes. Moreover, a planned geothermal system is often designed regardless of the presence of other existing or planned BHE systems. In order to evaluate the validity and the possible limitations of these assumptions commonly made by the designer, a number of 25-year time span simulations have been carried out by means of 2D finite element modeling. In particular, the case of a real 28 BHE field, irregularly shaped and related to a building located in Northern Italy, has been studied together with its 7-by-4 regular grid approximation and a series of 28 BHE fields having different shapes. Besides the real annual thermal load profile characterized by quasi-balanced winter heating and summer cooling, two other profiles characterized by increasingly unbalanced operation have been taken into account. The numerical study shows that (i) the regularly shaped approximation, a common choice in BHE design, seems to be reasonable under the condition that groundwater flow is absent for all the thermal load profiles; (ii) if a strong heating/cooling imbalance occurs, the thermal footprint of a BHE field can be very extensive, preventing the installation of future nearby BHE systems. © 2012 Elsevier Ltd
Strain rate computation in Northern Victoria Land (Antarctica) from episodic GPS surveys
No full textThe monitoring of crustal motions in Northern Victoria Land (NVL) of Antarctica by means of episodic GPS stations (EGPSs) provides an accurate and dense (∼50-km spaced) velocity field. The data, gathered starting in Austral summer 1999, derive from a series of benchmarks belonging to the Victoria Land Network for DEFormation control (VLNDEF) geodetic network. The velocity uncertainties are checked on the basis of length and returning time of the episodic surveys, to obtain a meaningful strain rate field by means of a least-square computation where the contribution of a GPS station is weighted by the inverse square of its velocity error. The study shows that the NVL is characterized by a complex kinematics and that, although three subregions with different prevailing deformational behaviour can be recognized, the single blocks cannot be resolved because too few stations exist. Only features having 150-200 km size at least can be recognized. Moreover, it is demonstrated that an appropriate data processing of EGPS data can lead to an accurate evaluation of the strain rate field even in a harsh environment like Antarctica. © 2012 The Authors Geophysical Journal International © 2012 RAS
Grid_strain and grid_strain3: Software packages for strain field computation in 2D and 3D environments
No full textTwo MatlabTM software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least-square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude points too far from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations (strain ≈10-8-10-6) or rapid landslide collapses (10-4-102), and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided. © 2008 Elsevier Ltd. All rights reserved
Hacking the topographic ruggedness index
No full textThe topographic ruggedness index (TRI) is widely adopted for the analysis of digital elevation models, providing information on local surface spatial variability. In this work, the TRI is interpreted according to a geostatistical perspective, highlighting its main characteristics and drawbacks. TRI can be interpreted as an omnidirectional short-range spatial variability index, computed according to a pixel centered perspective. The simplicity and interpretability of the index, free from user-dependent selections, promoted its implementation in several software environments and its application in a wide set of case studies. However, the index has several drawbacks for its application in earth sciences, such as a strong dependency on local slope (it is basically an average adjacent neighbor slope algorithm) and the selection of different lag distances in the computation of spatial variability along the main directions and the diagonal ones. We propose a new metric radial roughness index (RRI) in order to solve the main drawbacks of TRI but maintaining its main philosophy (i.e., pixel centered perspective and simplicity of the algorithm). The new index corrects for the differences in lag distances and resolves the dependency on trend using increments of order 2. The code of the index, implemented in R statistical language, and test data are provided with the paper (https://doi.org/10.5281/zenodo.7132160) to promote its implementation in other software environments
Effects of surface irregularities on intensity data from laser scanning: an experimental approach.
Full text linkThe results of an experiment carried out with the aim to investigate the role of surface irregularities on the intensity data provided by a terrestrial laser scanner (TLS) survey are reported here. Depending on surface roughness, the interaction between an electromagnetic wave and microscopic irregularities leads to a Lambertian-like diffusive light reflection, allowing the TLS to receive the backscattered component of the signal. The described experiment consists in a series of TLS-based acquisitions of a rotating artificial target specifically conceived in order to highlight the effects on the intensity data due to surface irregularity. This target is articulated in a flat plate and in an irregular surface, whose macro-roughness has a characteristic length with the same order of the spot size. Results point out the different behavior of the plates. The intensity of the signal backscattered by the planar element decreases if the incidence angle increases, whereas the intensity of the signal backscattered by the irregular surface is almost constant if the incidence angle varies. Since the typical surfaces acquired in a geological/geophysical survey are generally irregular, these results imply that the intensity data can be easily used in order to evaluate the reflectance of the material at the considered wavelength, e.g. for pattern recognition purposes
Contactless recognition of concrete surface damage from laser scanning and curvature computation
No full textA method conceived for automatic recognition of mass loss of concrete using data acquired by terrestrial laser scanner is presented here. The method is based on computation of mean and Gaussian curvatures of the surface and on piecewise comparison of the corresponding distributions, since these distributions strongly change if an area is affected by damage. This contactless damage recognition system, which could be applied together with other NDT techniques to provide a complete picture of the health of the observed structure, has been successfully applied to a concrete bridge. © 2008 Elsevier Ltd. All rights reserved
SURMODERR: A MATLAB toolbox for estimation of velocity uncertainties of a non-permanent GPS station
No full textSURMODERR is a MATLAB toolbox intended for the estimation of reliable velocity uncertainties of a non-permanent GPS station (NPS), i.e. a GPS receiver used in campaign-style measurements. The implemented method is based on the subsampling of daily coordinate time series of one or more continuous GPS stations located inside or close to the area where the NPSs are installed. The continuous time series are subsampled according to real or planned occupation tables and random errors occurring in antenna replacement on different surveys are taken into account. In order to overcome the uncertainty underestimation that typically characterizes short duration GPS time series, statistical analysis of the simulated data is performed to estimate the velocity uncertainties of this real NPS. The basic hypotheses required are: (i) the signal must be a long-term linear trend plus seasonal and colored noise for each coordinate; (ii) the standard data processing should have already been performed to provide daily data series; and (iii) if the method is applied to survey planning, the future behavior should not be significantly different from the past behavior. In order to show the strength of the approach, two case studies with real data are presented and discussed (Central Apennine and Panarea Island, Italy). © 2010 Elsevier Ltd
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