The Use of Ground Penetrating Radar and Microwave Tomography for the Detection of Decay and Cavities in Tree Trunks

Acknowledgements This paper is dedicated to the memory of Jonathan West; a friend, a colleague, a forester, a conservationist and an environmentalist, who died following an accident in the woodland that he loved.Peer reviewedPublisher PD

TeraHertz inspections of painted steel samples

International audienceAerospace industry needs accurate coating thickness measurement as well as adhesion testing for preventing the corrosion of wear of metal substrates. Recently, a constant attention is focused towards the potentialities offered by non-invasive sensing techniques and their technological advancements. This communication deals with time of flight THz imaging, enhanced by a noise filtering procedure based on the Singular Value Decomposition of the data matrix. In this work, THz imaging is exploited to analyse painted steel samples in order to detect paint coating layers and provide images of them and of the interface between the coating layer and the steel substrate

GPR and microwave tomography for the assessment of hollowed tree trunks

The danger related to the structural stability of hollowed trees is a matter of wide discussion among the scientific community. Hollow cores in trees can extend to more than 50% of the total diameter [1] and, while the presence of a hollow tree might appear dramatic in terms of public safety, it is not always a cause of concern. It is known that hollow trees can form in many years or even decades [2] and, although the heartwood is effectively dead, the tree can continue to form sapwood on the exterior of the trunk to create a cylinder. However, robustness and structural support provided by this cylinder to the trunk and canopy above depend on the ratio of healthy to diseased tissue. In this context, Ground Penetrating Radar (GPR) has proven to be an effective non-invasive tool, capable of generating information about the inner structure of tree trunks in terms of existence, location, and geometry of defects [3], [4]. Nevertheless, it had been observed that the currently available and known GPR-related processing and data interpretation methods and tools are able to provide only limited information on the tree inner structure. In this study, we present a microwave tomographic approach for improved GPR data processing with the aim of detecting and characterising the geometry of hollowed trees. Tests were performed at Gunnesbury Park, London, UK. In particular, a number of 15 circular measurements were collected around the tree using the Aladdin 2 GHz hand-held antenna system manufactured by IDS GeoRadar (Part of Hexagon), covering a height of 140 cm. The tree was eventually felled and three sections were cut for validation purposes. Results presented in this abstract are part of a major research project that the authors have undertaken for the last three years

X-Band Wave Radar for Coastal Upwelling Detection off the Southern Coast of Sicily

AbstractThe main aim of this work is to show the potentialities of an X-band radar system about the detection of the coastal upwelling phenomenon. This is made possible by means of the estimation of the sea surface current, which moves from the coastal areas toward the open sea for wind-induced upwelling events. The study presents the results of the X-band radar data processing for a system installed at Capo Granitola (southwestern Sicily). In particular, the radar data acquired in three different periods—namely, 5–6 November 2013, 8–9 February 2015, and 6 March 2015—indicated upwelling events. The occurrence of these events was confirmed by independent information derived from in situ wind data provided by a meteorological station and the analysis of the satellite-derived sea surface temperature (SST) and chlorophyll-a (Chl-a) concentration

Stereo imaging and X-band radar wave data fusion: An assessment

The use of spatial and spatio-temporal data is rapidly changing the paradigm of wind wave observations, which have been traditionally restricted to time series from single-point measurements (e.g. from buoys, wave gauges). Active and passive 2D remote sensors mounted on platforms, ships, airplanes and satellites are now becoming standards in the oceanographic community and industry. Given the covered area ranging from centimeters to kilometers, such sensors are now a valuable tool for ocean and coastal observations. In this paper, we intercompare spatio-temporal wind wave data acquired with two state-of-the-art techniques, namely the stereo wave imaging and the X-band marine radar. The comparison was performed by operating the two instruments on an oceanographic research platform during a crossing-sea condition. We analyzed the statistical properties of the wave field, and its directional and omni-directional energy distributions. From our analysis, we suggest that stereo data can be exploited to find the best radar Modulation Transfer Function and scale factor needed to estimate wave parameters. Moreover, the fusion of the two systems will allow to broaden the scales covered by any one measurement, and to retrieve reliable directional wave spectra from short (∼1 m) to mid-wavelengths (∼100 m)

Application of X-Band Wave Radar for Coastal Dynamic Analysis: Case Test of Bagnara Calabra (South Tyrrhenian Sea, Italy)

Sea state knowledge has a key role in evaluation of coastal erosion, the assessment of vulnerability and potential in coastal zone utilization, and development of numerical models to predict its evolution. X-band radar measurements were conducted to observe the spatial and temporal variation of the sea-state parameters along a 3 km long sandy-gravelly pocket beaches forming a littoral cell on Bagnara Calabra. We produced a sequence of 1000 images of the sea state extending offshore up to 1 mile. The survey has allowed monitoring the coastline, the directional wave spectra, the sea surface current fields, and the significant wave heights and detecting strong rip currents which cause scours around the open inlets and affect the stability of the submerged reef-type breakwaters. The possibility to validate the data acquired with other datasets (e.g., LaMMA Consortium) demonstrates the potential of the X-band radar technology as a monitoring tool to advance the understanding of the linkages between sea conditions, nearshore sediment dynamics, and coastal change. This work proves the possibility to obtain relevant information (e.g., wave number, period, and direction) for evaluation of local erosion phenomena and of morphological changes in the nearshore and surf zone

A Microwave Tomography Strategy for Underwater Imaging via Ground Penetrating Radar

Detection and monitoring of underwater structures is one of the most challenging applicative scenarios for remote sensing diagnostic techniques, among which ground penetrating radar (GPR). With this aim, an imaging strategy belonging to the family of microwave tomographic approaches is proposed herein. This strategy allows the imaging of objects located into a wet sand medium below a freshwater layer and it can find application in investigation of lakes, rivers, and hydraulic structures. The proposed strategy accounts for the layered structure of the scenario under test by exploiting a spatially variable equivalent permittivity in the inverse scattering model. This allows a reliable reconstruction of depth and horizontal size of underwater hidden objects. The imaging capabilities of the strategy are verified by processing experimental data referred to a laboratory environment reproducing a submerged archeological site at scale 1:1. The results are compared with those obtained by modelling the reference scenario as a homogeneous medium, in order to verify the effective improvement in terms of reconstruction accuracy

Estimation of the Significant Wave Height from Marine Radar Images without External Reference

In the context of the sea state monitoring by means of the X-band marine radar, the estimation of a significant wave height ( H s ) is, currently, one of the most challenging tasks. For its estimation, a calibration is usually required using an external reference, such as in situ sensors, and mainly buoys. In this paper, a method that allows us to avoid the need for an external reference for H s estimation is presented. This strategy is, mainly, based on the correlation between a raw radar image and the corresponding non-calibrated wave elevation image to which varying its amplitude by using a scale factor creates a mathematical model for the radar imaging. The proposed strategy has been validated by considering a simulated waves field, generated at varying sea state conditions. The results show a good estimation of the significant wave height, confirmed by a squared correlation coefficient greater than 0.70 for each considered sea state

Editorial for Special Issue “Radar Technology for Coastal Areas and Open Sea Monitoring”

The sea has always played a fundamental role in the social and economic development, as well as in the shaping and functioning of natural ecosystems and services [...