Machine Learning for Arctic Sea Ice Physical Properties Estimation Using Dual-Polarimetric SAR Data

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This work introduces a novel method that combines machine learning (ML) techniques with dual-polarimetric (dual-pol) synthetic aperture radar (SAR) observations for estimating quad-polarimetric (quad-pol) parameters, which are presumed to contain geophysical sea ice information. In the training phase, the output parameters are generated from quad-pol observations obtained by Radarsat-2 (RS2), and the corresponding input data consist of features obtained from overlapping dual-pol Sentinel-1 (S1) data. Then, two, well-recognized ML methods are studied to learn the functional relationship between the output and input data. These ML approaches are the Gaussian process regression (GPR) and neural network (NN) for regression models. The goal is to use the aforementioned ML techniques to generate Arctic sea ice information from freely available dual-pol observations acquired by S1, which can, in general, only be generated from quad-pol data. Eight overlapping RS2 and S1 scenes were used to train and test the GPR and NN models. Statistical regression performance measures were computed to evaluate the strength of the ML regression methods. Then, two scenes were selected for further evaluation, where overlapping optical images were available as well. This allowed the visual interpretation of the maps estimated by the ML models. Finally, one of the methods was tested on an entire S1 scene to perform prediction on areas outside of the RS2 and S1 overlap. Our results indicate that the studied ML techniques can be utilized to increase the information retrieval capacity of the wide swath dual-pol S1 imagery while embedding physical properties in the methodology

The design of hardware and signal processing for a stepped frequency continuous wave ground penetrating radar

Includes bibliographical references.A Ground Penetrating Radar (GPR) sensor is required to provide information that will allow the user to detect, classify and identify the target. This is an extremely tough requirement, especially when one considers the limited amount of information provided by most GPRs to accomplish this task. One way of increasing this information is to capture the complete scattering matrix of the received radar waveform. The objective of this thesis is to develop a signal processing technique to extract polarimetric feature vectors from Stepped Frequency Continuous Wave (SFGWV) GPR data. This was achieved by first developing an algorithm to extract the parameters from single polarization SFCW GPR data and then extending this algorithm to extract target features from fully polarimetric data. A model is required to enable the extraction of target parameters from raw radar data. A single polarization SFCW GPR model is developed based on the radar geometry and linear approximations to the wavenumber in a lossy medium. Assuming high operating frequencies and/or low conductive losses, the model is shown to be equivalent to the exponential model found in signal processing theory. A number of algorithms exist to extract the required target parameters from the measured data in a least squared sense. In this thesis the Matrix Pencil-of-Function Method is used. Numerical simulations are presented to show the performance of this algorithm for increasing model error. Simulations are also provided to compare the standard Inverse Discrete Fourier Transform (IDFT) with the algorithm presented in this thesis. The processing is applied to two sets of measured radar data using the radar developed in the thesis. The technique was able to locate the position of the scatterers for both sets of data, thus demonstrating the success of the algorithm on practical measurements. The single polarization model is extended to a fully polarimetric SFCW GPR model. The model is shown to relate to the multi-dimensional exponential signal processing model, given certain assumptions about the target scattering damping factor. The multi-snapshot Matrix Pencil-of-Function Method is used to extract the scattering matrix parameters from the raw polarimetric stepped frequency data. Those Huynen target parameters that are independent of the properties of the medium, are extracted from the estimated scattering matrices. Simulations are performed to examine the performance of the algorithm for increasing conductive and dielectric losses. The algorithm is also applied to measured data for a number of targets buried a few centimeters below the ground surface, with promising results. Finally, the thesis describes the design and development of a low cost, compact and low power SFCW GPR system. It addresses both the philosophy as well as the technology that was used to develop a 200 - 1600 MHz and a 1 - 2 GHz system. The system is built around a dual synthesizer heterodyne architecture with a single intermediate frequency stage and a novel coherent demodulator system - with a single reference source. Comparison of the radar system with a commercial impulse system, shows that the results are of a similar quality. Further measurements demonstrate the radar performance for different field test cases, including the mapping of the bottom of an outdoor test site down to 1.6 m

Enhanced Microwave Imaging of the Subsurface for Humanitarian Demining Applications

© Cranfield University 2020. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright ownerThis thesis presents a theoretical analysis and applied evaluation deploying ground penetrat ing radar (GPR) for landmine detection. An original contribution has been made in designing and manufacturing a light-weight, low-cost, fully polarimetric antenna system for GPR, enabling easy transportation and as sembly. This facilitates extensive use by various smaller communities in remote areas. By achieving the goal of supplying various smaller communities with advanced ground pene trating radar technology the technological standard of landmine detection can be improved beyond existing solutions such as metal detection or manual probing. The novel radar system itself allows detection of various subsurface targets of different shapes and sizes, metallic and non-metallic, in a number of different soils, such as sand, loam or gravel and therefore can be used in versatile environments. The GPR system has been realised by designing novel light-weight, 3D printed X-band horn antennas, manufactured from single piece plastic then copper electroplated. These an tennas are 50% lighter than their commercial equivalents. They are incorporated in an an tenna array as a group of four to allow full-polarimetric imaging of the subsurface. High resolution images of landmines and calibration targets were performed in the subsurface over an experimental sand test bed. For performing subsurface measurements in the near-field, four novel gradient-index (GRIN) lenses were designed and 3D printed to be incorporated in the apertures of the X band antennas. The improved target detection from these lenses was proven by scanning the test bed and comparing the imaging data of the antenna array with and without lenses attached. A rigorous theoretical study of different decomposition techniques and their effect on the imaging and detection accuracy for polarimetric surface penetrating data was performed and applied to the gathered imaging data to reliably isolate and detect subsurface targets. Studied decomposition techniques were Pauli decomposition parameters and Yamaguchi polarime try decomposition. It was found that it is paramount to use both algorithms on one set of subsurface data to detect all features of a buried target. A novel temporal imaging technique was developed for exploiting natural occurring changes in soil moisture level, and hence its dielectric properties. Contrary to the previously intro duced imaging techniques this moisture change detection (MCD) mechanism does not rely on knowledge of the used measurement setup or deploying clutter suppression techniques. This time averaged technique uses several images of a moist subsurface taken over a period while the moisture evaporates from the soil. Each image pixel is weighted by the phase change occurring over the evaporation period and a resulting B-scan image reveals the subsurface targets without surrounding clutter. Finally, a multi-static antenna set-up is examined on its capability for suppressing sur face clutter and its limitations are verified by introducing artificial surface clutter in form of pebbles to the scene. The resulting technique was found to suppress up to 30 The GPR antenna system developed in this thesis and the corresponding imaging tech niques have contributed to a significant improvement in subsurface radar imaging perfor mance and target discrimination capabilities. This work will contribute to more efficient landmine clearance in some of the most challenged parts of the world.Ph

Enhanced microwave imaging of the subsurface for humanitarian demining applications

© Cranfield University 2020. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright ownerThis thesis presents a theoretical analysis and applied evaluation deploying ground penetrating radar (GPR) for landmine detection. An original contribution has been made in designing and manufacturing a light-weight, low-cost, fully polarimetric antenna system for GPR, enabling easy transportation and assembly. This facilitates extensive use by various smaller communities in remote areas. By achieving the goal of supplying various smaller communities with advanced ground penetrating radar technology the technological standard of landmine detection can be improved beyond existing solutions such as metal detection or manual probing. The novel radar system itself allows detection of various subsurface targets of different shapes and sizes, metallic and non-metallic, in a number of different soils, such as sand, loam or gravel and therefore can be used in versatile environments. The GPR system has been realised by designing novel light-weight, 3D printed X-band horn antennas, manufactured from single piece plastic then copper electroplated. These antennas are 50% lighter than their commercial equivalents. They are incorporated in an antenna array as a group of four to allow full-polarimetric imaging of the subsurface. High resolution images of landmines and calibration targets were performed in the subsurface over an experimental sand test bed. For performing subsurface measurements in the near-field, four novel gradient-index (GRIN) lenses were designed and 3D printed to be incorporated in the apertures of the Xband antennas. The improved target detection from these lenses was proven by scanning the test bed and comparing the imaging data of the antenna array with and without lensesattached. A rigorous theoretical study of different decomposition techniques and their effect on the imaging and detection accuracy for polarimetric surface penetrating data was performed and applied to the gathered imaging data to reliably isolate and detect subsurface targets. Studied decomposition techniques were Pauli decomposition parameters and Yamaguchi polarimetry decomposition. It was found that it is paramount to use both algorithms on one set of subsurface data to detect all features of a buried target. A novel temporal imaging technique was developed for exploiting natural occurring changes in soil moisture level, and hence its dielectric properties. Contrary to the previously introduced imaging techniques this moisture change detection (MCD) mechanism does not rely on knowledge of the used measurement setup or deploying clutter suppression techniques. This time averaged technique uses several images of a moist subsurface taken over a period while the moisture evaporates from the soil. Each image pixel is weighted by the phase change occurring over the evaporation period and a resulting B-scan image reveals the subsurface targets without surrounding clutter. Finally, a multi-static antenna set-up is examined on its capability for suppressing surface clutter and its limitations are verified by introducing artificial surface clutter in form of pebbles to the scene. The resulting technique was found to suppress up to 30 The GPR antenna system developed in this thesis and the corresponding imaging techniques have contributed to a significant improvement in subsurface radar imaging performance and target discrimination capabilities. This work will contribute to more efficient landmine clearance in some of the most challenged parts of the world

On the use of lateral wave for the interlayer debonding detecting in an asphalt airport pavement using a multistatic GPR system

In this paper, we focus on the detection of the interlayer debonding of the asphalt airport pavement by the Ground-penetrating Radar (GPR) system. Since the interlayer debonding usually occurs in the shallow region of the asphalt airport pavement (several centimeters), it is difficult to interpret the anomalies or the defects from the GPR signals composed of many waves under the boundary conditions. Moreover, the wavelength of the ordinary GPR system is over several centimeters. Therefore, the spatial resolution of the system is not accurate enough to consider the millimeter thickness of the debonding layer. To overcome these problems, we propose a new method based on evaluating the lateral wave behavior of common midpoint (CMP) gathers collected by a multiple static GPR system. The multi-static GPR system is a stepped frequency continuous wave (SFCW) radar system, which consists of 8 transmitting and 8 receiving bowtie antennas. The system operates in the frequency range from 50 MHz to 1.5 GHz. After the validation of the simulation, the results of the interlayer debonding detection were evaluated by a field experiment obtained at Tokyo International Airport. The proposed method can detect the debonding layers which are less than 1mm. Also, it is shown that our proposed method has a high consistency with the conventional acoustic finding method in the field measurement. It provides an innovative and effective method for the interlayer debonding detection of a partially damaged airport asphalt pavement, which is difficult to be observed by the ordinary GPR signals

Ground, Proximal, and Satellite Remote Sensing of Soil Moisture

Soil moisture (SM) is a key hydrologic state variable that is of significant importance for numerous Earth and environmental science applications that directly impact the global environment and human society. Potential applications include, but are not limited to, forecasting of weather and climate variability; prediction and monitoring of drought conditions; management and allocation of water resources; agricultural plant production and alleviation of famine; prevention of natural disasters such as wild fires, landslides, floods, and dust storms; or monitoring of ecosystem response to climate change. Because of the importance and wide‐ranging applicability of highly variable spatial and temporal SM information that links the water, energy, and carbon cycles, significant efforts and resources have been devoted in recent years to advance SM measurement and monitoring capabilities from the point to the global scales. This review encompasses recent advances and the state‐of‐the‐art of ground, proximal, and novel SM remote sensing techniques at various spatial and temporal scales and identifies critical future research needs and directions to further advance and optimize technology, analysis and retrieval methods, and the application of SM information to improve the understanding of critical zone moisture dynamics. Despite the impressive progress over the last decade, there are still many opportunities and needs to, for example, improve SM retrieval from remotely sensed optical, thermal, and microwave data and opportunities for novel applications of SM information for water resources management, sustainable environmental development, and food security

Guidebook on Detection Technologies and Systems for Humanitarian Demining

The aim of this publication is to provide the mine action community, and those supporting mine action, with a consolidated review and status summary of detection technologies that could be applied to humanitarian demining operations. This Guidebook is meant to provide information to a wide variety of readers. For those not familiar with the spectrum of technologies being considered for the detection of landmines and for area reduction, there is a brief overview of the principle of operation for each technology as well as a summary listing of the strengths, limitations, and potential for use of the technology to humanitarian demining. For those with an intermediate level of understanding for detection technologies, there is information regarding some of the more technical details of the system to give an expanded overview of the principles involved and hardware development that has taken place. Where possible, technical specifications for the systems are provided. For those requiring more information for a particular system, relevant publications lists and contact information are also provided

M-sequenze based ultra-wideband radar and its application to crack detection in salt mines

Die vorliegende Dissertation beschreibt einen innovativen ultra-breitband (UWB)elektromagnetischen Sensor basierend auf einem Pseudo-Rauschverfahren.Der Sensor wurde für zerstörungsfreies Testen in zivilen Anwendungen entwickelt.Zerstörungsfreies Testen entwickelt sich zu einem immer wichtiger werdenden Bereich in Forschung und Entwicklung. Neben unzähligen weiteren Anwendungen und Technologien, besteht ein primäres Aufgabenfeld in der Überwachung und Untersuchung von Bauwerken und Baumaterialien durch berührungslose Messung aus der Ferne.Diese Arbeit konzentriert sich auf das Beispiel der Auflockerungszone im Salzgestein.Der Hintergrund und die Notwendigkeit, den Zustand der oberflächennahen Salzschichten in Salzminen kennen zu müssen, werden beleuchtet und die Messaufgabe anhand einfacher theoretischer Überlegungen beschrieben. Daraus werden die Anforderungen für geeignete UWB Sensoren abgeleitet. Die wichtigsten Eigenschaften sind eine sehr hohe Messband breite sowie eine sehr saubere Systemimpulsantwort frei von systematischen Gerätefehlern. Beide Eigenschaften sind notwendig, um die schwachen Rückstreuungen der Auflockerungen trotz der unvermeidlichen starken Oberflächenreflexion detektieren zu können.Da systematische Fehler bei UWB Geräten technisch nicht von vorne herein komplett vermeidbar sind, muss der Sensor eine Gerätekalibrierung erlauben, um solche Fehler möglichst gut zu unterdrücken.Aufgrund der genannten Anforderungen und den Nebenbedingungen der Messumgebung unter Tage, wurde aus den verschiedenen UWB-Technologien ein Prinzip ausgewählt, welches pseudozufällige Maximalfolgen als Anregungssignal benutzt. Das M-Sequenzkonzept dient als Ausgangpunkt für zahlreiche Weiterentwicklungen. Ein neues Sendemodul erweitert dabei die Messbandbreite auf 12~GHz. Die äquivalente Abtastrate wird um den Faktor vier auf 36~GHz erhöht, ohne den geringen Abtastjitter des ursprünglichen Konzepts zu vergrössern.Weiterhin wird die Umsetzung eines Zweitormesskopfes zur Erfassung von S-Parametern sowie einer automatische Kalibriereinheit beschrieben. Etablierte Kalibrierverfahren aus dem Bereich der Netzwerkanalyse werden kurz rekapituliert und die Adaption des 8-Term Verfahrens mit unbekanntem Transmissionsnormal für das M-Sequenzsystem beschrieben. Dabei werden Kennwerte vorgeschlagen, die dem Bediener unter Tage einfach erlauben, die Kalibrierqualität einzuschätzen und Hinweise auf mögliche Gerätefehler oder andere Probleme zu bekommen. Die Kalibriergenauigkeit des neuen Sensors im Labor wird mit der eines Netzwerkanalysators verglichen. Beide Geräte erreichen eine störungsfreie Dynamik von mehr als 60~dB in den Systemimpulsantworten für Reflexion und Transmission.Der neu entwickelte UWB Sensor wurde in zahlreichen Messungen in Salzminen in Deutschland getestet. Zwei Messbeispiele werden vorgestellt - ein sehr alter, kreisrunder Tunnel sowie ein ovaler Tunnelstumpf, welcher kurz vor den Messungen erst aufgefahren wurde. Messaufbauten und Datenverarbeitung werden beschrieben. Schließlich werden Schlussfolgerungen und Vorschläge für zukünftige Arbeiten mit dem neuen M-Sequenzsensor sowie der Messung von Auflockerungen im Salzgestein diskutiert.This dissertation describes an innovative ultra-wideband (UWB) electromagnetic sensor device based on a pseudo-noise principle developed in the context of non-destructive testing in civil engineering.Non-destructive testing is becoming a more and more important fieldfor researchers and engineers alike. Besides the vast field of possibleapplications and testing technologies, a prime and therefore typical topic is the inspection and monitoringof constructions and materials by means of contactless remote sensing techniques.This work focuses on one example the assessment of the disaggregation zone in salt rock tunnels.The background and relevance of knowing the state of salt rock layers near a tunnel's surface are explainedand simple theoretical considerations for requirements of suitable UWB sensor devices are shown. The most important sensor parameters are a very large measurement bandwidth and a very clean impulse response. The latterparameter translates into the mandatory application of calibration techniques to remove systematic errors of the sensor system itself. This enables detection of weak scattering responses from near-surface disaggregation despite the presence of a strong surface reflection.According to the mentioned requirements and other side conditions in salt mine environments an UWB sensor principlebased on pseudo-noise stimuli namely M-Sequences is selected as a starting point for system development. A newtransmitter frontend for extending the stimulus bandwidth up to 12~GHz is presented. Furthermore, a technique for increasing the (equivalent) sampling rate while keeping the stable and low-jitter sampling regime of the M-Sequencesapproach is introduced and its implementation is shown. Moreover, an automatic calibration unit for full two-port coaxial calibration of the new UWB sensor has been developed. Common calibration techniques from the area of vector network analysers are shortly reviewed and a reasonablealgorithm the 8-term method with an unknown line standard - is selected for the M-Sequences device. The 8-term method is defined in the frequency domain and is adapted for use with time domain devices. Some performance figures and comparisonwith calibration results from network analysers are discussed to show the effectiveness of the calibration.A spurious-free dynamic range of the time domain impulse responses in excess of 60~dB has been achieved for reflection as well as transmission measurements.The new UWB sensor was used in various real world measurements in different salt mines throughout Germany. Two measurementexamples are described and results from the disaggregation zone of a very old and a freshly cut tunnel will be presented. Measurement setup and data processing are discussed and finally some conclusions for future work on this topic are drawn

An evaluation of the performance of multi-static handheld ground penetrating radar using full wave inversion for landmine detection

This thesis presents an empirical study comparing the ability of multi-static and bi-static, handheld, ground penetrating radar (GPR) systems, using full wave inversion (FWI), to determine the properties of buried anti-personnel (AP) landmines. A major problem associated with humanitarian demining is the occurrence of many false positives during clearance operations. Therefore, a reduction of the false alarm rate (FAR) and/or increasing the probability of detection (POD) is a key research and technical objective. Sensor fusion has emerged as a technique that promises to significantly enhance landmine detection. This study considers a handheld, combined metal detector (MD) and GPR device, and quantifies the advantages of the use of antenna arrays. During demining operations with such systems, possible targets are detected using the MD and further categorised using the GPR, possibly excluding false positives. A system using FWI imaging techniques to estimate the subsurface parameters is considered in this work.A previous study of multi-static GPR FWI used simplistic, 2D far-field propagation models, despite the targets being 3D and within the near field. This novel study uses full 3D electromagnetic (EM) wave simulation of the antenna arrays and propagation through the air and ground. Full EM simulation allows the sensitivity of radio measurements to landmine characteristics to be determined. The number and configuration of antenna elements are very important and must be optimised, contrary to the 2D sensitivity studies in (Watson, Lionheart 2014, Watson 2016) which conclude that the degree (number of elements) of the multi-static system is not critical. A novel sensitivity analysis for tilted handheld GPR antennas is used to demonstrate the positive impact of tilted antenna orientation on detection performance. A time domain GPR and A-scan data, consistent with a commercial handheld system, the MINEHOUND, is used throughout the simulated experiments which are based on synthetic GPR measurements.Finally, this thesis introduces a novel method of optimising the FWI solution through feature extraction or estimation of the internal air void typically present in pressure activated mines, to distinguish mines from non-mine targets and reduce the incidence of false positives

Synthetic aperture radar imaging system for landmine detection using a ground penetrating radar on board a unmanned aerial vehicle

This paper presents a novel system to obtain images from the underground based on ground penetrating radar (GPR). The proposed system is composed by a radar module mounted on board an unmanned aerial vehicle (UAV), which allows the safe inspection of difficult-to-access areas without being in direct contact with the soil. Therefore, it can be used to detect dangerous buried objects, such as landmines. The radar measurements are coherently combined using a synthetic aperture radar (SAR) algorithm, which requires cm-level accuracy positioning system. In addition, a clutter removal technique is applied to mitigate the reflection at the air-soil interface (which is caused by impedance mismatching). Besides the aforementioned advantages, the system can detect both metallic and dielectric targets (due to the use of a radar instead of a metal detector) and it allows to obtain high-resolution underground images (due to the SAR processing). The algorithms and the UAV payload are validated with measurements in both controlled and real scenarios, showing the feasibility of the proposed system.Ministerio de Economía y Competitividad | Ref. TEC2014-54005-PMinisterio de Economía y Competitividad | Ref. TEC2014-55290-JINMinisterio de Economía y Competitividad | Ref. TEC2015-73908-JINMinisterio de Economía y Competitividad | Ref. TEC2015-65353-RAgencia Estatal de Investigación | Ref. RYC-2016-20280Ministerio de Educación | Ref. FPU15/06341Gobierno del Principado de Asturias | Ref. PCTI 2013-2017Gobierno del Principado de Asturias | Ref. FC-15-GRUPIN14-114Gobierno del Principado de Asturias | Ref. IDI/2017/000095Xunta de Galicia | Ref. GRC2015/01