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Properties Of Concrete

Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.

Water on Mars

The new level of precision and global coverage provided by satellite altimetry is rapidly advancing studies of ocean circulation. It allows for new insights into marine geodesy, ice sheet movements, plate tectonics, and for the first time provides high-resolution bathymetry for previously unmapped regions of our watery planet and crucial information on the large-scale ocean features on intra-season to interannual time scales. Satellite Altimetry and Earth Sciences has integrated the expertise of the leading international researchers to demonstrate the techniques, missions, and accuracy of satellite altimetry, including altimeter measurements, orbit determination, and ocean circulation models. Satellite altimetry is helping to advance studies of ocean circulation, tides, sea level, surface waves and allowing new insights into marine geodesy. Satellite Altimetry and Earth Sciences provides high resolution bathymetry for previously unmapped regions of our watery planet. Satellite Altimetry and Earth Sciences is for a very broad spectrum of academics, graduate students, and researchers in geophysics, oceanography, and the space and earth sciences. International agencies that fund satellite-based research will also appreciate the handy reference on the applications of satellite altimetry.

Satellite altimetry and Earth sciences :a handbook of techniques and applications

Spaceborne differential synthetic aperture radar interferometry (DInSAR) has already proven its potential for mapping ground deformation phenomena, e.g. volcano dynamics. However, atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability. These drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors (Permanent Scatterers, PS) and exploiting long temporal series of interferometric data. Results obtained by processing 55 images acquired by the European Space Agency (ESA) ERS SAR sensors over Southern California show that the PS approach pushes measurement accuracy very close to its theoretical limit (about 1 mm), allowing the description of millimetric deformation phenomena occurring in a complex fault system. A comparison with corresponding displacement time series relative to permanent GPS stations of the Southern California Integrated GPS network (SCIGN) is carried out. Moreover, the pixel-by-pixel character of the PS analysis allows the exploitation of individual phase stable radar targets in low-coherence areas. This makes spaceborne interferometric measurements possible in vegetated areas, as long as a sufficient spatial density of individual isolated man-made structures or exposed rocks is available. The evolution of the Ancona landslide (central Italy) was analysed by processing 61 ERS images acquired in the time span between June 1992 and December 2000. The results have been compared with deformation values detected during optical levelling campaigns ordered by the Municipality of Ancona. The characteristics of PS, GPS and optical levelling surveying are to some extent complementary: a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring. D 2002 Elsevier Science B.V. All rights reserved.

Monitoring Landslides and Tectonic Motions with the Permanent Scatterers Technique

Communication systems: An introduction to signals and noise in electrical communication

Management and conservation of natural heritage are becoming increasingly important as health of ancient trees is threatened by the presence of unknown and aggressive pathogens [1]. In this regard, root systems are threatened by fungal infections inducing rotting of roots and eventually leading to death of trees. These infections may easily spread to nearby trees and affect larger areas. As these decays may not show evident symptoms, an early-stage identification is crucial to protect trees.
In this context, non-destructive testing (NDT) methods are gaining momentum as they are faster and more
versatile than destructive techniques. Specifically, ground penetrating radar (GPR) has emerged as an increasingly reliable geophysical inspection method for mapping tree roots [2]. Automated algorithms for tracking roots in a three-dimensional environment have been developed [3]. More recently, interconnections between tree roots of different tree species have been investigated based on mass density distributions of roots in depth [4].
The aim of this research is to improve upon existed methods and provide a more commercially appealing
framework for root characterisation. To this extent, advanced signal processing – both in time and frequency
domain - is applied in an effort to reduce false alarms and retain a high probability of root detection. In addition, data collected on various types of trees using different antenna systems and survey methodologies are processed to investigate how these parameters affect the overall performance of GPR.
Results presented in this abstract are part of a major research project that the authors have undertaken for the last two years.

Advances in Ground Penetrating Radar Signal Processing for Mapping Tree Root Systems

Ground-penetrating radar (GPR) is considered as one of the most flexible geophysical tools that can be effectively and efficiently used in many different applications. In the field of pavement engineering, GPR can cover a wide range of uses, spanning from physical to geometrical inspections of pavements. Traditionally, such inferred information are integrated with mechanical measurements from other traditional (e.g. plate bearing test) or non-destructive (e.g. falling weight deflectometer) techniques, thereby resulting, respectively, in time-consuming and low-significant measurements, or in a high use of technological resources. In this regard, the new challenge of retrieving mechanical properties of road pavements and materials from electromagnetic measurements could represent a further step towards a greater saving of economic resources. As far as concerns unpaved and bound layers it is well-known that strength and deformation properties are mostly affected, respectively, by inter-particle friction and cohesion of soil particles and aggregates, and by bitumen adhesion, whose variability is expressed by the Young modulus of elasticity. In that respect, by assuming a relationship between electromagnetic response (e.g. signal amplitudes) and bulk density of materials, a reasonable correlation between mechanical and electric properties of substructure is therefore expected. In such framework, a pulse GPR system with ground-coupled antennae, 600 MHz and 1600 MHz centre frequencies was used over a 4-m×30-m test site composed by a flexible pavement structure. The horizontal sampling resolution amounted to 2.4×10-2 m. A square regular grid mesh of 836 nodes with a 0.40-m spacing between the GPR acquisition tracks was surveyed. Accordingly, a light falling weight deflectometer (LFWD) was used for measuring the elastic modulus of pavement at each node. The setup of such instrument consisted of a 10-kg falling mass and a 100-mm loading plate so that the influence domain of the elasticity measure could be comparable to that of the radar signal. Good agreement were found between high Young modulus values and repaved zones, whereas damaged areas were characterized by lower values of E. Tomographic maps of amplitudes along the z axis were extracted up to a depth of z < 200 mm, consistent with the depth domain of the LFWD, and some values on the nodes were randomly selected and thus related to the corresponding elastic modulus both for calibration and validation of the model. Comparison between predicted and measured elastic modulus showed relatively good results. Percentage errors ranging from -44% and +34% demonstrated an overall underestimate of the model with respect to the real truth. Future research activities could be addressed towards an improvement of the model by calibrating in laboratory environment under controlled conditions, and by using different GPR centre frequencies of investigation. This work benefited from networking activities carried out within the EU funded COST Action TU1208 “Civil Engineering Applications of Ground Penetrating Radar”.

Investigation of mechanical properties of pavement through electromagnetic techniques

Ground-penetrating radar (GPR) is being increasingly used for pavements maintenance due to the wide range of
applications spanning from physical to geometrical inspections, thereby allowing for a reliable diagnosis of the main causes of road structural damages.
In this work, an off-ground GPR system was used to investigate a large-scale rural road network. Two sets of
surveys were carried out in different time periods, with the main goals to i) localize the most critical sections; ii) monitor the evolution of previous damages and localize newborn deep faults, although not revealed at the pavement surface level; iii) analyze the causes of both evolution and emergence of faults by considering environmental and human factors.
A 1-GHz GPR air-launched antenna was linked to an instrumented van for collecting data at traffic speed. Other support techniques (e.g. GPS data logger, odometer, HD video camera) were used for cross-checking,. Such centre frequency of investigation along with a 25-ns time window allow for a signal penetration of 900 mm, consistent with the deepest layer interfaces. The bottom of the array was 400 mm over the surface, with a minimum distance of 1200 mm from the van body. Scan length of maximum 10 km were provided for avoiding heavy computational loads.
The rural road network was located in the District of Rieti, 100 km north from Rome, Italy, and mostly develops
in a hilly and mountainous landscape. In most of the investigated roads, the carriageway consists in two lanes of 3.75 meters wide and two shoulders of 0.50 meters wide. A typical road section includes a HMA layer (65 mm
average thickness), a base layer (100 mm average thickness), and a subbase layer (300 mm average thickness), as described by pavement design charts.
The first set of surveys was carried out in two days at the beginning of spring in moderately dry conditions.
Overall, 320-km-long inspections were performed in both travel directions, thereby showing a productivity of
approximately 160 km/day at 40 km/h speed, on the average.
After processing and first-checking, GPR profiles were divided into homogeneous sections according to the combination of different parameters (e.g. route analyzed, long distance conditions of regularity/irregularity in layers arrangement). In such context, a high consistency between surface damages, mismatches from the GPR scans,
and boundary environmental conditions was demonstrated. In addition, deep mismatches were detected even for
early-stage or unrevealed faults.
The second set of surveys was carried out in autumn in high humidity conditions, due to recent rainfalls. 160 km
of relevant routes from the same road network were investigated.
Results showed a high consistency with those collected during the first-stage of surveys. Minor changes were
found in those sections with low traffic loads (e.g. farther away from the biggest town of Rieti), whereas major mismatches were detected in wetlands (e.g. close to rivers), work zones, and nearby those sections already deeply damaged in the past.
This work benefited from networking activities carried out within the EU funded COST Action TU1208 “Civil
Engineering Applications of Ground Penetrating Radar”.

On-site inspections of pavement damages evolution using GPR

In this work, a novel signal processing framework for polarimetric GPR measurements is presented for inspection of tree trunks’ decay. The framework combines a polarimetric noise filter and an arc-shaped diffraction imaging algorithm. The polarimetric noise filter can increase the signal-to-noise ratio (SNR) of B-scans caused by the bark and the high-loss propriety of the tree trunk based on a 3D Pauli feature vector of the Bragg scattering theory. The arc-shaped diffraction stacking and an imaging aperture are then designed to suppress the effects of the irregular shape of the tree trunk on the signal. The proposed detection scheme is successfully validated with real tree trunk measurements. The viability of the proposed processing framework is demonstrated by the high consistency between the results and the real-truth trunk cross-sections.

/pdf/tree-trunk-inspections-using-a-polarimetric-gpr-system-8fufs7z19i.pdf

Tree trunk inspections using a polarimetric GPR system

Street trees are broadly acknowledged to be an essential asset of cities. Nonetheless, the growth of tree roots can lead to critical damage, such as the uplifting or cracking of road pavements and curbs, with severe implications on the infrastructure’s safety. For this reason, the assessment and control of tree root systems’ development have become crucial task in forestry and urban management. Within this framework, Ground Penetrating Radar (GPR) is widely recognised as an effective non-destructive testing (NDT) method for the monitoring and assessment of road infrastructures. This study aims to demonstrate the capability of GPR in mapping the root system’s architecture of street trees. To this end, a GPR system equipped with a 700 MHz central frequency antenna was employed to investigate the area around a street tree, located in the vicinity of a flexible pavement structure. A novel processing framework based on the analysis of the signal reflectivity was implemented, in order to automatically identify the reflections from the pavement layers and apply dedicated advanced signal processing techniques. A multistage data processing methodology was employed to map the tree root system architecture. Finally, information on the mass density of roots at different depths was also provided. Results have proven the potential of the proposed methodology to achieve an automatic detection and mapping of roots under road pavements.

/pdf/a-reflectivity-based-gpr-signal-processing-methodology-for-450pa9z6o4.pdf

Fabio Tosti

Papers

Advances in Ground Penetrating Radar Signal Processing for Mapping Tree Root Systems

Investigation of mechanical properties of pavement through electromagnetic techniques

On-site inspections of pavement damages evolution using GPR

Tree trunk inspections using a polarimetric GPR system

A Reflectivity-Based GPR Signal Processing Methodology for Mapping Tree Root Systems of Street Trees