- [Show abstract] [Hide abstract] ABSTRACT: This paper describes a project entitled 'ORFEUS' supported by the European Commission's 7th Framework development programme. Horizontal directional drilling (HDD) offers significant benefits for urban environments by minimising the disruption caused by street works. Use of the technique demands an accurate knowledge of underground utility assets and other obstructions in the drill path. This project is aimed at improving the results of a previous project developed under the 6th Framework programme; specifically it addresses some issues that were formerly unresolved, in order to produce a commercially viable product. In fact, ORFEUS activities concern the research of the optimum antenna configuration, the design of an angular position sensor and a communication module, as well as the identification/validation of the most effective bore-head GPR data processing algorithms. The final system is expected to offer the operator information directly from the drilling head, in real time, allowing objects to be avoided; this is a unique feature that will enhance safety and efficiency, reduce risk, reduce the environmental impact (e.g. damage to natural habitats, less CO2 emissions) and lead to positive economic benefits in terms of cost and time savings for the operator, manufacturers and wider supply chain.
- [Show abstract] [Hide abstract] ABSTRACT: Measurement of molten glass level in glass furnaces is a key issue for the control of the production process. Nowadays several different technologies shall be used for this purpose, with their advantages and drawbacks. In this paper a novel level sensor is proposed, it is based on radar interferometry technique, and it is designed to provide high accuracy measurements, high reliability and a very low maintenance.
- [Show abstract] [Hide abstract] ABSTRACT: Interferometric radar is a rather popular equipment able to remotely perform dynamic testing of large structures (towers, bridges, buildings …) by detecting the relative displacement in the line of sight between the radar and geometric discontinuities in the engineering structure under test. This technique has been demonstrated effective when the radar is positioned at ground on a stable position. Unfortunately there are practical cases for which a suitable stable position is not available. This is the case of the towers of San Gimignano (Italy) that are embedded in the narrow streets of the old town. A solution to monitor the towers is to install the radar on the top of a tower, which is located in a central position of the town. The tower is not a stable arrangement for the radar and in this paper the authors propose and test the use of an accelerometer fixed to the radar head for detecting and removing its own movement.
- [Show abstract] [Hide abstract] ABSTRACT: Interferometric radars are sensors able to remotely detect the dynamic displacements of large structures such as bridges and towers, but they have to be positioned on stable ground. There are several applications for which this limitation is critical, so in this paper the authors propose and evaluate in field a possible solution for overcoming this requirement. The basic premise is to install an accelerometer inside the radar head to detect its own movement. This device with suitable data process chain, in the best conditions, is able to mitigate the effects of movements of the radar head above 30 dB. Lower values have been obtained in operative conditions.
- [Show abstract] [Hide abstract] ABSTRACT: Ground-based radar interferometry is an increasingly popular technique for monitoring civil infrastructures. In this paper, the static testing of a bridge is reported. It was an 8-span bridge, 297 m long, named "Ponte degli Alpini," crossing the valley of the Ardo River. The radar has been used for testing a lateral span and a central span. The obtained results present elements of novelty not previously reported in the literature. In fact, some displacement measurements of the lateral span have been affected by a horizontal shift that has to be taken into account for a correct interpretation of the measured data. Furthermore, the measurements of the central span have been carried out with the radar positioned transversally with respect to the bridge deck; this unusual arrangement has allowed for obtaining displacement maps less geometrically distorted with respect to other cases reported in the literature.
Conference Paper: A reconfigurable stepped frequency GPR (GPR-R): The antenna subsystem[Show abstract] [Hide abstract] ABSTRACT: GPR-R technology fully exploits the unique advantages of the stepped frequency radar technique. A GPR equipment based on this technology has been recently developed by the authors: it is able to reconfigure its integration time and transmitted power vs. frequency in order to increase penetration capability and radiofrequency interference immunity. This paper describes the antenna subsystem of this radar.
Conference Paper: Radar gauge for molten glass level measurement[Show abstract] [Hide abstract] ABSTRACT: Level gauges for glass furnaces are critical control elements in the production process. The authors designed and tested an interferometric radar with characteristics and performances meeting the harsh working conditions in a glass furnace and the strict issues of this kind of sensor. The equipment has been tested in a real furnace.
Conference Paper: Landslide observation by ground-based SAR interferometry[Show abstract] [Hide abstract] ABSTRACT: A ground-based synthetic aperture radar (GB-SAR) system was installed for the observation and monitoring of post-landslide slope in Kurihara-city, Miyagi, Japan. The system is operated at 17 GHz (Ku-band) with a frequency bandwidth of 150 MHz. Horn antennas scan about 2 m horizontally to cover a large observation area and SAR processing is applied to achieve higher azimuth and range resolutions. In addition, the interferometric technique is used to detect very small changes on the target, resulting in the expected interferometer resolution of 0.1 mm. In 2011, the system operated from November to December to acquire preliminary results and to study the feasibility of the technique for monitoring landslide surface. During the period, major events on the landslide surface did not happen and, thus, no significant changes were detected by the GB-SAR system. However, it detected small movements at some locations approaching to the system that is likely caused by a snowfall. It demonstrates the capability of the GB-SAR technique in detecting very small changes on a target.
- [Show abstract] [Hide abstract] ABSTRACT: A novel ground based multi bistatic interferometric radar sensor has been realized in order to measure the three dimensional displacement vector of civil structures as buildings, bridges and towers. Data processing techniques were developed to determine the position of each target and to calculate three dimensional displacement starting from mono dimensional displacement measured from three different positions in space. Experimental tests were finally carried out in controlled environment in order to validate the proposed technique and to assess the accuracy of displacement’s measurement.
- [Show abstract] [Hide abstract] ABSTRACT: Large bandwidth microwave signals propagate in dispersive media as pulses that attenuate according to a non-exponential law. Although this is a direct consequence of wellknown theory of propagation in dispersive media, this fact is rarely acknowledged. The aim of this paper is an experimental study of this effect in fresh water and wet sand, both media of interest in Ground Penetrating Radar, which performances dramatically rely on capability of microwaves to propagate through soil.
- [Show abstract] [Hide abstract] ABSTRACT: Radar data collected at an experimental facility arranged on purpose suggest that the footprint of atmospheric turbulence might be encoded in the radar signal statistics. Radar data probability distributions are calculated and nicely fitted by a one-parameter family of generalized Gumbel (GG) distributions, Ga. A relation between the wind strength and the measured shape parameter a is obtained. Strong wind fluctuations return pronounced asymmetric leptokurtic profiles, while Gaussian profiles are eventually recovered as the wind fluctuations decrease. Besides stressing the crucial impact of air turbulence for radar applications, we also confirm the adequacy of Ga statistics for highly correlated complex systems.
- [Show abstract] [Hide abstract] ABSTRACT: A novel Ground Based Synthetic Aperture Interferometric radar was set up for slope stability monitoring in open pit quarries. It is a wide view angle system which is easily adapted to the typical geometry of a quarry, and it automatically generates interferometric DEMs of the area under investigation. The system was tested during a 40 days field survey in a stone quarry in Tuscany, Italy.
- [Show abstract] [Hide abstract] ABSTRACT: Large bandwidth microwave signals propagating in dispersive media can result in pulses decaying according to a non-exponential law. In particular, large bandwidth signals in the microwave band, propagating in media that can be described by the Debye model (for example fresh water), decays as the square root of the inverse of the propagation distance, instead of exponentially. Although it is a direct consequence of well-known theory of propagation in dispersive media, this result is a bit surprising and its experimental evidence has required a careful set-up.
- [Show abstract] [Hide abstract] ABSTRACT: Belvedere Glacier, east face of the Mount Rosa, has experienced drastic changes in flow regime and morphology in the last years. Within the activities of the GALAHAD project funded by the European Commission, a ground-based SAR (GB-SAR) interferometer was employed on this glacier. Although based on the ground, the sensor works with the same principles as satellite radar interferometry measuring the deformation field of the illuminated surface. It was used for the first time on this glacier in 2004 and a new survey, here reported, was arranged last summer (2007). During this latter survey, the radar antenna moved around a vertical axis in order to illuminate a larger part of the glacier. It provided deformation maps of a wider part of the glacier every half an hour almost continually for 1 month. Finally, a procedure for building a digital elevation model (DEM) of the glacier was developed and the obtained DEM was compared with an available topographic map dated July 2005. Large differences in the ice surface height appear from the comparison confirming the overall reduction of the ice mass.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, we report on an experimental activity aimed at investigating the potential of two terrestrial remote-sensing techniques, namely, ground-based SAR (GB SAR) interferometry and terrestrial laser scanning, in order to retrieve snow-depth (SD) measurements in mountainous regions. Terrestrial laser scanning is a more consolidated technique based on the measurement of the optical (near infrared) reflectivity, and it is affected by the surface of the snow layer: a temporal data sequence allows us to estimate the absolute SD variation. Recent use of SAR interferometry to evaluate snow-mass characteristics is based on relating the measured interferometric phase shift to a change in the snow mass. Interferometric GB SAR measurements and terrestrial laser scanner scans were collected together with pointwise conventional measurements of physical snow parameters during the winters of 2005/2006 and 2006/2007. The experiment was carried out in the Wattener Lizum, a high Alpine area at about 2000-m elevation north of the main ridge of the Austrian Alps in Tyrol. Notwithstanding the difficulty of providing both lengthy data record in dry snow conditions and detailed knowledge of the observed snow characteristics, the obtained results confirmed the presence of a clearly measurable interferometric phase variation in relation to the growing height of the snow layer. A comparison of the SD maps obtained through the two techniques shows differences partly due to the different nature of the two observations.
- [Show abstract] [Hide abstract] ABSTRACT: This work reports on the results obtained with a high speed ground based radar interferometer applied to the monitoring of the explosive activity of Stromboli volcano, Italy. The sensor illuminated a few craters below the summit distinguishing among them according to their distances from the sensor. The sampling rate allowed tracking the craters' movements even while they were erupting providing information about both the area affected from the deformation and its extent. Radar data were compared with seismic signals from the permanent monitoring network. The comparison demonstrated that the radar interferometer is a powerful device for retrieving ground deformation before and after an explosive event. In particular, eruptions were clearly identified from the observation of peculiar characteristics of the amplitude, phase and coherence data.
- [Show abstract] [Hide abstract] ABSTRACT: Belvedere Glacier, east face of the Mount Rosa, has experienced drastic changes in flow regime and morphology in the last years. Within the activities of the European project GALAHAD a Ground Based SAR (GB-SAR) interferometer was employed for the first time on this glacier. In the present work it is reported how the sensor capability of generating digital elevation models (DEMs) was exploited in order to retrieve information about the occurred surface changes. In particular, in this case study, the DEM obtained by the radar on summer 2007 was compared with two previous DEMs from other sources: one relative to summer 2005 and the other to summer 1995. Significant differences in the ice surface height have appeared from the comparison reflecting both the extraordinary surge type movement occurred in 2003-2004 and afterwards the overall reduction of the ice mass.
- [Show abstract] [Hide abstract] ABSTRACT: Terrestrial laser scanner (TLS) and interferometric synthetic aperture radar (InSAR) allow the acquisition of data on an observed surface with high spatial sampling rate. The data provided by TLS observation of a landslide ground surface can be used to generate a very detailed digital model of this surface, and multitemporal observations with TLS or continuous or multitemporal observation with InSAR can provide a reliable displacement map. In order to acquire useful information about the analogies, differences, and capabilities, as well as limitations of these techniques, a joint experimentation of TLS and InSAR was performed over two years in various sites in the Italian Alps. The results have indicated that these techniques can provide high‐quality data, can be very useful in the monitoring intended for the mitigation of hydrogeological risk in a wide range of cases, and must be supported by a topographical georeferenced network.
University of Florence
Florens, Tuscany, Italy
- Dipartimento di Ingegneria dell'Informazione