Littérature scientifique sur le sujet « Holographic subsurface RADAR »

Holographic subsurface radar (HSR) is not currently in widespread usage. This is due to a historical perspective in the ground-penetrating radar (GPR) community that the high attenuation of electromagnetic waves in most media of interest and the inability to apply time-varying gain to the continuous-wave (CW) HSR signal preclude sufficient effective penetration depth. While it is true that the fundamental physics of HSR, with its use of a CW signal, does not allow amplification of later (i.e., deeper) arrivals in lossy media (as is possible with impulse subsurface radar (ISR)), HSR has distinct advantages. The most important of these is the ability to do shallow subsurface imaging with a resolution that is not possible with ISR. In addition, the design of an HSR system is simpler than for ISR due to the relatively low-tech transmitting and receiving antennae. This paper provides a review of the main principles of HSR through an optical analogy and describes possible algorithms for radar hologram reconstruction. We also present a review of the history of development of systems and applications of the RASCAN type, which is possibly the only commercially available holographic subsurface radar. Among the subsurface imaging and remote sensing applications considered are humanitarian demining, construction inspection, nondestructive testing of dielectric aerospace materials, surveys of historic architecture and artworks, paleontology, and security screening. Each application is illustrated with relevant data acquired in laboratory and/or field experiments.

The NATO SPS G-5014 project has shown the possibility of using a holographic RADAR for the detection of anti-personnel mines. To use the RADAR on a robotic scanning system, it must be portable, light, easily integrated with mechanical handling systems and configurable in its operating parameters for optimal performance on different terrains. The novel contribution is to use software programmable electronics to optimize performance and to use a time reference to obtain synchronization between the RADAR samples and the position in space, in order to make it easy to integrate the RADAR on robotic platforms. To achieve these goals we used the Analog Devices “ADALM Pluto” device based on Software Defined Radio technology and a time server. We have obtained a portable system, configurable via software in all its operating parameters and easily integrated on robotic scanning platforms. The paper will show experiments performed on a simulated minefield. The electronics project reported in this work makes holographic RADARs portable and easily reconfigurable, therefore adaptable to different applications from subsurface soil investigations to applications in the field of non-destructive testings.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

In our experiments, we develop and test portable multi-element receiver antenna arrays, electrically scanned in order to immediately obtain a recognizable image of subsurface objects. Two quadrature components of the radar return signal are processed with a Kirchhoff backward migration algorithm. Physical theory is used to assess the quality of the holographic image, and the synthetic aperture approach is developed and tested. The parabolic wave equation and Gaussian beam technique are used in order to take into account refraction effects and to suppress specular reflection from the air-ground interface. Laboratory and field tests confirmed the predicted device parameters.

Per mezzo del finanziamento ottenuto con il progetto North Atlantic Treaty Organization, Science for Peace and Security (NATO SPS) G-5014 è stata sviluppata una piattaforma robotica multi-sensore in grado di individuare oggetti sepolti plastici e metallici e generare dati per la successiva classificazione degli ordigni attraverso l’analisi di operatori specializzati. Utilizzare una piattaforma robotica permette di aumentare la sicurezza per gli operatori, perché completamente controllabile in remoto tramite un’interfaccia software web e permette di utilizzare diversi sensori per massimizzare la probabilità di rivelazione delle mine, mantenendo minima la probabilità di ricevere falsi allarmi. I sensori principali installati sono due RADAR operanti nello spettro delle microonde ( ≃2 GHz): un UWB Ground Penetrating RADAR (GPR), sviluppato appositamente per rilevare la posizione dell’oggetto sepolto all’interno dell’area illuminata, capace di rilevare oggetti sepolti durante il moto della piattaforma e un Holographic Subsurface RADAR (HSR), operante ad onda continua e singola frequenza, in grado di generare immagini olografiche che permettono di osservare la forma e le dimensioni degli oggetti sepolti nei primi 15 - 20 cm del sottosuolo e, tramite l’elaborazione con algoritmi di inversione del campo elettromegnetico, permette di ricostruire la scena tridimensionale che si trova di fronte all’apertura sintetica del RADAR. Le immagini che genera questo dispositivo consentono di discriminare gli ordigni da altri oggetti riflettenti le microonde ma del tutto inoffensivi (clutter). Il HSR progettato nel corso del progetto NATO SPS G-5014 costituisce un primo prototipo che soddisfava i requisiti richiesti dal progetto. Il frutto di questo lavoro ha riscosso interesse nella comunità scentifica e presso NATO SPS, generando un seguito: il progetto NATO SPS G-5731, tutt’ora in corso. Nell’ambito di quest’ultimo progetto si colloca il mio lavoro: ho contribuito allo sviluppo di un sistema RADAR per immagini a microonde in grado di migliorare, in termini di qualità di immagini prodotte (incrementando il rapporto segnale-rumore e la risoluzione) e di profondità di penetrazione (studiando le caratteristiche elettromagnetiche del suolo di interesse), le prestazioni del HSR. Mi sono occupato di individuare i parametri su cui poter intervenire: la risoluzione ottenibile applicando la matematica dell’olografia, le tecniche e gli algoritmi di inversione del campo elettromagnetico, lo studio dell’ambiente elettromagnetico irradiato e i requisiti dell’elemento radiante (tipo di antenna, forma, dimensioni, potenza irradiata) reailzzandone uno con la tecnologia della stampa tridimensionale. Ho valutato e studiato una soluzione per migliorare la compatibilità elettromagnetica con il sistema robotico su cui dovrà operare il RADAR. Per realizzare un prototipo funzionante mi sono occupato di definire i requisiti dell’elettronica di pilotaggio e della programmazione dei dispositivi implementati. Questo testo si conclude con la dimostrazione, mediante l’esposizione di prove sperimentali in ambiente controllato, delle prestazioni del nuovo RADAR, evidenziandone le differenze rispetto al HSR originale. ------------- Thanks to the funding obtained with the North Atlantic Treaty Organization, Science for Peace and Security (NATO SPS) G-5014 project, a multi-sensor robotic platform was developed capable of identifying buried plastic and metal objects and generating data for subsequent classification. of ordnance through the analysis of specialized operators. Using a robotic platform allows you to increase safety for operators, because it can be completely remotely controlled via a web software interface and allows you to use different sensors to maximize the probability of mine detection, while keeping the probability of receiving false alarms to a minimum. The main sensors installed are two RADARs operating in the microwave spectrum (≃2 GHz): a UWB Ground Penetrating RADAR (GPR), specially developed to detect the position of the buried object within the illuminated area, capable of detecting buried objects during the motion of the platform and a Holographic Subsurface RADAR (HSR), operating at continuous wave and single frequency, capable of generating holographic images that allow to observe the shape and dimensions of the objects buried in the first 15 - 20 cm of the subsoil and, through the processing with electromagnetic field inversion algorithms, it allows to reconstruct the three-dimensional scene that is in front of the synthetic opening of the RADAR. The images that this device generates allow to discriminate the bombs from other objects reflecting the microwaves but completely harmless (clutter). The HSR designed during the NATO SPS G-5014 project constitutes a first prototype that met the requirements of the project. The fruit of this work has attracted interest in the scientific community and at NATO SPS, generating a sequel: the NATO SPS G-5731 project, which is still underway. My work is part of this last project: I contributed to the development of a RADAR system for microwave images capable of improving, in terms of the quality of images produced (by increasing the signal-to-noise ratio and resolution) and depth of penetration (studying the electromagnetic characteristics of the soil of interest), the performance of the HSR. I worked on identifying the parameters on which to intervene: the resolution obtainable by applying the mathematics of holography, the techniques and algorithms of electromagnetic field inversion, the study of the radiated electromagnetic environment and the requirements of the radiant element (type of antenna , shape, size, radiated power) by realizing one with the technology of three-dimensional printing. I have evaluated and studied a solution to improve the electromagnetic compatibility with the robotic system on which the RADAR will have to operate. To create a working prototype, I worked on defining the requirements of the driving electronics and programming of the implemented devices. This text ends with the demonstration, through the display of experimental tests in a controlled environment, of the performance of the new RADAR, highlighting the differences compared to the original HSR.