ABSTRACT Over the last decades, remote sensing techniques have been exhibiting a great performance by measuring and monitoring a process without physically touching the target under observation. It has opened up a new path by exploring the Earth from Space. Whereas the early development of optical satellite sensors has become a reliable source to provide a great deal of information on the Earth’s surface, today the limitations of passive sensors can be significantly overcome by the active sensors. This thesis examines various attempts to illustrate the significant role of an active remote sensing sensor such as radar, especially where the environmental and geophysical sciences are concerned. As an all- weather remote sensing system, radar can monitor the Earth’s surface or atmospheric features through the emission of artificial radiation. This is even more considerable due to the fact that the atmospheric effects are minimized by penetrating the clouds, light rain and snow. In essence, a variety of information sources (e.g., surface roughness, moisture content of soil layer, and dielectric properties) can be collected from the radar operation in wavelengths outside the visible and infrared regions of the electromagnetic (EM) spectrum corresponding to microwave wavelengths. As for these particular characteristics of radar, the concentration of this thesis is based on the two different operations of the radar system on the subject of environmental and geophysical observations. First, one of the most widely used active microwave sensors with a moving antenna, so-called Synthetic Aperture Radar (SAR) and following that, one of the most powerful geophysical tools for subsurface remote sensing, so-called Ground Penetration Radar (GPR), are pondered. Thoroughly, the application of SAR on the wildfire monitoring of the second largest Italian Island (Sardinia), using the post- fire detection, is examined in terms of a backscattering coefficient- sigma naught- difference (∆σ°) and Projected Local Incident Angle (PLIA). This is where SAR data provides us with more information to accurately identify the burnt regions due to seasonal wildfires. A detailed analysis of VH and VV polarization images has revealed that the cross-polarized imagery in the ascending pass produces a higher value of ∆σ° between two consecutive SAR images. Afterwards, the second application of radar as the performance of airborne-based GPR on the basis of sending the EM waves vertically down to and capturing the reflected waves is pored over glaciers. It allows us to gain insight into subglacial conditions (e.g., the bedrock) for two different glacial structures of the Alps and Antarctica. Technically, the shape of the ice bed/the ice thickness measurement is a leading evidence for the ice moves in the passing periods. In so doing, this study attempts to spotlight the capability of different radar sensors to record surface and/or subsurface features for environmental and geophysical monitoring. The remainder of the thesis also proposes another perspective of SAR technology in geophysics- so called SAR Tomography (TomoSAR), which implements the multiple SAR images recorded from slightly different looking angles to reconstruct the L-band 3D imaging of an Austrian Alpine glacier for the first time. It signifies the performance of TomoSAR as an advanced compatible geophysical tool, where the airborne TomoSAR sections are directly compared against the corresponding profiles of a well validated geophysical tool such as the ground-based GPR by sampling TomoSAR cubes along GPR transects for investigating the ice subsurface. Different subsurface features (e.g., firn bodies, crevasses, and also the ice bed down to a few tens of meters below the surface topography), scrutinized in GPR transects at 600 MHz and 200 MHz, distinctly are turned up on TomoSAR sections. This accentuates the significance of further studies to probe the potential of Tomo-SAR technology in geophysical observations of glaciers in particular.
RIASSUNTO Durante gli ultimi decenni le tecniche di telerilevamento hanno consentito di ottenere ottimi risultati attraverso la misura e il monitoraggio di processi senza aver quindi bisogno di toccare fisicamente i target in questione. Ciò ha aperto nuove strade di esplorazione della terra dallo spazio. Anche se i primi sviluppi dei sensori satellitari ottici hanno rappresentato una fonte affidabile per procurare una grande quantità di informazioni riguardo alla superficie della terra, attualmente le limitazioni dei sensori passive possono essere ampiamente superate dai sensori attivi. Questa tesi esamina vari approcci con lo scopo di illustrare l'importanza del ruolo di un particolare sensore attivo come il radar, nell’ambito delle scienze ambientali e geofisiche. Essendo uno dei sensori all-weather, il radar e’ in grado di monitorare la superficie della terra o le caratteristiche atmosferiche attraverso l'emissione di radiazioni artificiali. Ciò diventa ancora piu rilevante se si pensa al fatto che gli effetti dell'atmosfera vengono ridotti attraversando nuvole, pioggia e neve. In sostanza, diverse tipi di informazione (per esempio la scabrosita’ della superficie, l’umidita’ degli strati di suolo e le proprieta’ dielettriche) possono essere raccolte dal radar operando con lunghezze d'onda al di fuori dello spettro visibile e degli infrarossi dello spettro elettromagnetico, corrospondenti alle micronde. A causa di queste particolari caratteristiche del radar, l'attenzione in questa tesi si e’ focalizzata su due diverse funzioni del radar. Innanzitutto, verra’ trattato uno dei sensori a microonde più utilizzati con antenna mobile, il cosiddetto radar ad apertura sintetica (SAR) e successivamente, si parlera’ di uno dei più potenti strumenti geofisici per il telerilevamento del sottosuolo, il Ground Penetration Radar (GPR). Piu’ specificatamente, il SAR e’ stato applicato al monitoraggio degli incendi nella seconda più grande isola italiana (la Sardegna) utilizzando il rilevamento post-incendio, in termini di coefficienti di backscattering - sigma naught- (Δσ°) e Projected Local Incident Angle (PLIA). Grazie a questo sistema i dati SAR ci forniscono ulteriori informazioni per identificare con precisione le regioni colpite da incendi stagionali. L'analisi dettagliata delle immagini di polarizzazione VH e VV ha rivelato che l’ immagine cross-polarizzata in ascending pass produce un valore più alto di Δσ ° tra due immagini SAR consecutive. La seconda applicazione del radar e’ stata quella airborne based GPR, basato sull’invio delle onde EM verticalmente verso il basso e sullo studio accurato delle onde riflesse rilevate sopra ghiacciai. Questo ci ha consentito di valutare le condizioni subglaciali (ad esempio, della base) di due diverse strutture glaciali delle Alpi e dell'Antartide. Tecnicamente, la forma del letto del ghiacciaio e la misura dello spessore del ghiaccio è una traccia per comprendere i movimenti ghiaccio nei periodi di passaggio. In tal modo, questo studio tenta di fare luce sulla capacità dei diversi sensori radar di registrare le caratteristiche superficiali e/o del sottosuolo per il monitoraggio ambientale e geofisico. Il resto della tesi propone un’altra applicazione della tecnologia SAR in geophysica- il cosiddetto SAR Tomography (TomoSAR), che implementa le molteplici immagini SAR registrate da diverse angolazioni cercando di ricostruire l'imagine 3D in banda L di un ghiacciaio alpino austriaco. Cio’ significa adoperare TomoSAR come uno strumento avanzato compatibile a scopi geofisici, in cui le sezioni TomoSAR nell'aria sono direttamente confrontate con i corrispondenti profili di uno strumento di geofisica ampiamente validato come il GPR terrestre, campionando cubi di ghiaccio lungo transetti GPR per investigare il sottosuolo. Diverse caratteristiche del sottosuolo (ad esempio, corpi firn, crepacci, o anche il letto del ghiacciaio fino a poche decine di metri sotto la superficie topografica), sono esaminate nei transetti GPR a 600 MHz e 200 MHz, mostrate distintamente sulle sezioni TomoSAR. Questo enfatizza l’importanza di ulteriori studi per sondare le potenzialità della tecnologia Tomo-SAR in particolar modo per le analisi geofisiche dei ghiacciai.
Application of synthetic aperture radar (SAR) and ground penetration radar (GPR) in environmental and geophysical monitoring
PEIMAN, REIHANEH
2015/2016
Abstract
ABSTRACT Over the last decades, remote sensing techniques have been exhibiting a great performance by measuring and monitoring a process without physically touching the target under observation. It has opened up a new path by exploring the Earth from Space. Whereas the early development of optical satellite sensors has become a reliable source to provide a great deal of information on the Earth’s surface, today the limitations of passive sensors can be significantly overcome by the active sensors. This thesis examines various attempts to illustrate the significant role of an active remote sensing sensor such as radar, especially where the environmental and geophysical sciences are concerned. As an all- weather remote sensing system, radar can monitor the Earth’s surface or atmospheric features through the emission of artificial radiation. This is even more considerable due to the fact that the atmospheric effects are minimized by penetrating the clouds, light rain and snow. In essence, a variety of information sources (e.g., surface roughness, moisture content of soil layer, and dielectric properties) can be collected from the radar operation in wavelengths outside the visible and infrared regions of the electromagnetic (EM) spectrum corresponding to microwave wavelengths. As for these particular characteristics of radar, the concentration of this thesis is based on the two different operations of the radar system on the subject of environmental and geophysical observations. First, one of the most widely used active microwave sensors with a moving antenna, so-called Synthetic Aperture Radar (SAR) and following that, one of the most powerful geophysical tools for subsurface remote sensing, so-called Ground Penetration Radar (GPR), are pondered. Thoroughly, the application of SAR on the wildfire monitoring of the second largest Italian Island (Sardinia), using the post- fire detection, is examined in terms of a backscattering coefficient- sigma naught- difference (∆σ°) and Projected Local Incident Angle (PLIA). This is where SAR data provides us with more information to accurately identify the burnt regions due to seasonal wildfires. A detailed analysis of VH and VV polarization images has revealed that the cross-polarized imagery in the ascending pass produces a higher value of ∆σ° between two consecutive SAR images. Afterwards, the second application of radar as the performance of airborne-based GPR on the basis of sending the EM waves vertically down to and capturing the reflected waves is pored over glaciers. It allows us to gain insight into subglacial conditions (e.g., the bedrock) for two different glacial structures of the Alps and Antarctica. Technically, the shape of the ice bed/the ice thickness measurement is a leading evidence for the ice moves in the passing periods. In so doing, this study attempts to spotlight the capability of different radar sensors to record surface and/or subsurface features for environmental and geophysical monitoring. The remainder of the thesis also proposes another perspective of SAR technology in geophysics- so called SAR Tomography (TomoSAR), which implements the multiple SAR images recorded from slightly different looking angles to reconstruct the L-band 3D imaging of an Austrian Alpine glacier for the first time. It signifies the performance of TomoSAR as an advanced compatible geophysical tool, where the airborne TomoSAR sections are directly compared against the corresponding profiles of a well validated geophysical tool such as the ground-based GPR by sampling TomoSAR cubes along GPR transects for investigating the ice subsurface. Different subsurface features (e.g., firn bodies, crevasses, and also the ice bed down to a few tens of meters below the surface topography), scrutinized in GPR transects at 600 MHz and 200 MHz, distinctly are turned up on TomoSAR sections. This accentuates the significance of further studies to probe the potential of Tomo-SAR technology in geophysical observations of glaciers in particular.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/119221