1,720,987 research outputs found
Antonio Ventura
No full textLo scopo di questo lavoro di tesi è stato di valutare l'accuratezza metrica di un nuovo satellite indiano, Cartosat-1, sia per quanto riguarda l'orientamento delle immagini, sia per quanto riguarda la generazione di modelli digitali delle superfici.
Cartosat-1 è stato messo in orbita il 5 Maggio del 2005. La sua principale caratteristica è di avere a bordo due sensori di tipo pancromatico (ognuno con risoluzione spaziale di 2.5 m), capaci di osservare la stessa porzione di territorio da angoli di vista differenti. Lo scarto temporale tra le due acquisizioni della stessa zona, risulta molto ridotto (52 secondi). Questo breve intervallo di tempo facilita il processo di matching e permette la continua produzione di immagini stereo, cioè parzialmente sovrapposte ed adatte alla generazione di DSMs. Avendo a disposizione la stereocoppia acquisita sulla zona di Castelgandolfo, le immagini sono state orientate utilizzando sia il modello rigoroso, implementato nel programma commerciale PCI-Orthoengine, sia il modello generico degli RPC (Rapid Positioning Capability), implementato nei software scientifici SISAR e RAPORIO, sviluppati rispettivamente dall' Area di Geodesia e Geomatica - Sapienza Università degli studi di Roma- e dall' Institute of Photogrammetry and GeoInformation della Leibniz University di Hannover. Utilizzando entrambi i metodi è stato possibile ottenere un'accuratezza sull'orientamento dell'immagine inferiore alla dimensione del pixel, inoltre, i risultati dei diversi programmi usati sono pienamente confrontabili.
Partendo dalla stereocoppia Cartosat-1 di Castelgandolfo, il DSM è stato generato usando due metodi diversi di matching: il primo è il Least Squares Matching, utilizzato dal programma scientifico DPCOR (Leibniz University, Hannover), il secondo è il metodo della cross-correlazione, utilizzato dal programma PCI-Orthoengine.
Per valutare l'accuratezza del DSM generato da Cartosat-1, si è deciso di assumere come modello di confronto il DSM estratto da un blocco fotogrammetrico di 31 foto e di calcolare l’errore quadratico medio delle differenze di quota tra queste due superfici (RMSEz).
I confronti tra i DSMs sono statti condotti sia su tutta l'area di sovrapposizione, sia selezionando diverse tipologie di suolo: la tipologia cittadina di suolo urbano, e quella delle zone il più possibile prive di vegetazione e fabbricati (aperte). Tutte le prove sono state condotte due volte: prima direttamente sui DSMs estratti in seguito al matching, e poi sui relativi DEMs (Modelli Digitali delle Elevazioni), ottenuti applicando una funzione di filtro per rimuovere tutti gli elementi non appartenenti al terreno vero e proprio (alberi, palazzi, etc.). Dall' analisi sulle differenze di altezze tra i DSM nelle zone aperte, è stato ottenuto un RMSEz di 3.05 m, mentre, dopo aver applicato il filtro, l'RMSEz diminuisce a 2.41 m, scendendo quindi sotto la dimensione del pixel. Nelle zone urbane l'RMSEz si attesta attorno 4.73, diminuendo fino a 3.96 m in seguito all' applicazione del filtro. I risultati ricavati dal confronto tra i DEM dipendono però dalla tecnica di filtraggio utilizzata.
Come argomento di ricerca parallelo è stata valutata la capacità del programma SISAR di generare RPC per l'orientamento delle immagini e l'estrazione di modelli digitali del terreno. Utilizzando gli RPC generati dal programma, i quali sono 1/3 di quelli originali contenuti nei files di metadata, è stato possibile orientare la stereocoppia con un RMSEZ leggermente superiore al pixel. Il DSM generato a partire da questo orientamento presenta un'accuratezza pienamente confrontabile con quella del modello digitale ottenuto lavorando con gli RPC che vengono forniti insieme alle immagini originali.
In conclusione del lavoro si può affermare che la modalità di acquisizione di Cartosat-1 risulta ottimale per la generazione di modelli digitali delle superfici. Il ridotto intervallo temporale fra le due acquisizioni favorisce il procedimento di matching automatico. L'orientamento delle immagini non presenta particolari problemi, ed entrambi gli approcci utilizzati portano ad ottenere un'accuratezza inferiore alla dimensione del pixel. L'algoritmo di generazione degli RPC, implementato all'interno del programma SISAR, si è dimostrato in grado di fornire coefficienti che portano a risultati analoghi a quelli che si ottengono utilizzando gli RPC originali forniti insieme alle immagini, sia in fase di orientamento, sia in fase di generazione del modello digitale
Opticks SAR PlugIn
No full textThe Opticks' SAR PlugIn contains the main tools necessary for Synthetic Aperture Radar (SAR) imagery georeferencing, orthorectification and an handy tool to perform 3D stereo measurement for two SAR high resolution satellite sensors: RADARSAT-2 and TerraSAR-X.
In particular the PlugIn performs a robust rigorous orientation model, based on the two classical zero-doppler radargrammetric equations, in order to exploiting the full geolocation capabilities for this kind of sensors.
The tool undergoes continuous development in order to improve its capability, enrich its functionalities and include further satellite sensors
An open source Opticks plug-in for high resolution SAR imagery orthorectification and stereo measurements
No full textNowadays, the availability of novel high-resolution synthetic aperture radar (SAR) spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of secondary products as digital surface models (DSMs), orthoimages, and displacement maps. SAR technology provides for low-cost, fast data acquisition and processing, independence from logistic difficulties, and night-and-day and all-weather functionality. These features are of crucial importance for the timely monitoring and management of disasters and emergencies such as geological, hydrological, and geophysical hazards. However, one of the most critical aspects in extracting useful and reliable information from SAR data is the image processing. Although several commercial software suites are available, in recent years the open source technology has confirmed a reliable and effective alternative for SAR processing and in general for geospatial information management. For instance, projects such as the Open Source Geospatial Foundation (OSGeo) offer to users, developers, and scientists powerful solutions based on costless, expandable, and customizable software. The goal of this work was to extend the capabilities of the Opticks remote sensing and imagery analysis software developing a plug-in (3DGeoCode plug-in) able to perform SAR precise image orthorectification (Orthotool) and to retrieve three-dimensional information starting from a stereo-pair (stereo measurement tool). At the moment of writing this article, the plug-in handles high-resolution SAR imagery acquired by TerraSAR-X and Radarsat-2 sensors. A complete description of the exploited algorithms is illustrated with special focus on showing the solutions adopted during the implementation. Moreover, a deep analysis of the accuracy achievable by the 3DGeoCode plug-in is reported showing the results obtained in several test sites. In particular, using a high-resolution lidar DSM and a TerraSAR-X spotlight stereopair over the area of Trento city (northern Italy), a root mean square error (RMSE) of approximately 2–3 m with respect to the reference DSM both for orthoimages and stereo measurements was achieved
VADASE: Variometric Approach for Displacement Analysis Stand-alone Engine
No full textGlobal Navigation Satellite Systems (GNSS), like Global Positioning System (GPS), are nowadays very well known. Besides the mass market, GPS plays an important role in several technical and scientific activities. Ever since the early stages of development (mid 1980s), given the high level of accuracy achieved in determining the coordinates of the receiver, it became clear that the extensive deployment of GPS stations all over the world would have improved many tasks in geodesy and geodynamics.
In recent years, several studies have demonstrated the effective use of GPS in estimating coseismic displacement waveforms induced by an earthquake with accuracies ranging from a few millimeters to a few centimeters (so called GPS seismology). This contribution is particularly relevant as it supports the estimation of important seismic parameters (e.g. seismic moment and magnitude Mw) without the problems of saturation that commonly affect seismometers and accelerometers close to large earthquakes. These studies were developed mainly off-line, analyzing observations acquired during strong earthquakes. Then, well-known processing strategies (single Precise Point Positioning (PPP), and differential positioning) have been developed to reduce as far as possible the latency between earthquake occurrence and coseismic displacement waveforms estimation.
This work describes a new approach that was originally designed to detect the 3D displacements of a single GPS receiver in real-time and that was eventually appointed as an effective strategy to contribute to GPS seismology. The main goals that guided through the development aimed to obtain the coseismic displacement waveforms in real-time and using a single receiver. In particular, it was pursued to overcome the drawbacks of the two most common strategies used so far in GPS seismology: PPP uses a single receiver, but it requires ancillary products (e.g. information regarding satellites orbits, clocks; parameters describing the Earth orientation with respect to an external inertial system) currently unavailable in real-time. On the other hand, differential kinematic positioning is based on a complex infrastructure (GPS permanent network), which has to be managed by specialized research centers to obtain high accuracies in real-time.
The new approach proposed in this work, named Variometric Approach for Displacement Analysis Stand-alone Engine (VADASE), is based upon a so called variometric algorithm, which is able to use a single receiver to obtain real-time results, with accuracies ranging from few centimeters up to a couple of decimeters.
In order to prove the feasibility of the variometric algorithm, a tuned software, which was appointed with the same name (i.e. VADASE), was implemented. Exploiting this software to process a large amount of both simulated and real data, the main advantages of VADASE, as well as its limitations, were investigated in details.
At a first stage, VADASE effectiveness was proven on a simulated example. First, a known displacement (1 cm East and North and 2 cm Up) was synthetically introduced into carrier phase observations collected at 1 Hz rate by the M0SE permanent GPS station (Rome, Italy). Then, these data were processed using the variometric algorithm: the displacements were estimated with an accuracy of 1-2 mm in the horizontal and the vertical directions. The solutions obtained using the GPS broadcast products available in real-time and the best quality products supplied by IGS a posteriori displayed a global agreement of 1 mm for the horizontal components and 2 mm for the height.
Given this fundamental proof of success, and provided that the variometric algorithm was originally
conceived to contribute in the field of GPS seismology and tsunami warning systems, VADASE was applied to retrieve the coseismic displacements and the waveforms generated by real earthquakes. Here, it is worth underlining that all VADASE results were obtained using exclusively broadcast products that are available in real-time. The most significant outcomes were obtained by considering data collected at 1 Hz rate from the IGS station of BREW during the Denali Fault, Alaska earthquake (Mw 7.9, November 3, 2002), at 10 Hz rate from CADO station during the L'Aquila earthquake (Mw 6.3, April 6, 2009), and at 5 Hz rate from some stations included in the UNAVCO - PBO network during the Baja, California earthquake (Mw 7.2, April 4, 2010). In all cases, the agreement between VADASE and other solutions achieved by different research groups employing different methodologies was between few centimeters and a couple of decimeters.
The real-time potentialities of the variometric approach were internationally recognized during the recent tremendous earthquake in Japan (Mw = 9.0, March 11, 2011), when the GNSS research team of University of Rome "La Sapienza" was able to provide the first waveforms results among the scientific community. The results obtained for IGS stations of MIZU, USUD and from EV-network station JA01 were compared with those stemming from the PPP approach implemented in the software developed at Natural Resources Canada (NRCan). This work was made possible thanks to the precious support of Dr. Henton Joe and Dr. Dragert Herb, NRCan, who produced the PPP solutions for the aforementioned stations. The agreement between VADASE and PPP was evaluated in terms of the RMSE of the differences.
In addition, it was investigated the agreement reliance with the earthquake duration. The Root Mean Square Error (RMSE) of the differences between the two solutions ranged from 0.01-0.02 m in East and North and 0.06 m in Up, after one minute, to approximately 0.05 m in East and North and (with much larger variability) 0.20 m in Up after four minutes. Further, the agreement between the two approaches evaluated in terms of peak to peak displacements appeared to be independent from the earthquake duration. In details, the differences reached approximately 0.01 m in East and North and 0.03 m in Up components. Finally, the correlation coefficient between the two solutions proved to be higher than 99% for the planimetric components (but for the East component of USUD and the North component of JA01 which showed 97% and 96% correlations, respectively). The vertical component showed slightly lower (and with larger variability) correlations: 65%, 84% and 90% for stations MIZU, USUD and JA01, respectively.
At the moment of this writing, VADASE is subject of a pending patent of University of Rome “La Sapienza” ever since June 2010. In October 2010 VADASE was recognized as a simple and effective approach towards real-time coseismic displacement waveform estimation and it was awarded the German Aerospace Agency (DLR) Special Topic Prize and the First Audience Award in the European Satellite Navigation Competition 2010.Global Navigation Satellite Systems (GNSS), like Global Positioning System
(GPS), are nowadays very well known. Besides the mass market, GPS plays an
important role in several technical and scientific activities. Ever since the early
stages of development (mid 1980s), given the high level of accuracy achieved in
determining the coordinates of the receiver, it became clear that the extensive
deployment of GPS stations all over the world would have improved many tasks
in geodesy and geodynamics.
In recent years, several studies have demonstrated the effective use of GPS
in estimating coseismic displacement waveforms induced by an earthquake with
accuracies ranging from a few millimeters to a few centimeters (so called GPS
seismology). This contribution is particularly relevant as it supports the esti-
mation of important seismic parameters (e.g. seismic moment and magnitude
Mw ) without the problems of saturation that commonly affect seismometers and
accelerometers close to large earthquakes. These studies were developed mainly
off-line, analyzing observations acquired during strong earthquakes. Then, well-
known processing strategies (single Precise Point Positioning (PPP), and differ-
ential positioning) have been developed to reduce as far as possible the latency
between earthquake occurrence and coseismic displacement waveforms estima-
tion.
This work describes a new approach that was originally designed to detect the
3D displacements of a single GPS receiver in real-time and that was eventually ap-
pointed as an effective strategy to contribute to GPS seismology. The main goals
that guided through the development aimed to obtain the coseismic displacement
waveforms in real-time and using a single receiver. In particular, it was pursued
to overcome the drawbacks of the two most common strategies used so far in GPS
seismology: PPP uses a single receiver, but it requires ancillary products (e.g.
informations regarding satellites orbits, clocks; parameters describing the Earth
orientation with respect to an external inertial system) currently unavailable in
real-time. On the other hand, differential kinematic positioning is based on a
complex infrastructure (GPS permanent network), which has to be managed by
specialized research centers to obtain high accuracies in real-time.
The new approach proposed in this work, named Variometric Approach for
Displacement Analysis Stand-alone Engine (VADASE), is based upon a so called
variometric algorithm, which is able to use a single receiver to obtain real-time
results, with accuracies ranging from few centimeters up to a couple of decimeters.
In order to prove the feasibility of the variometric algorithm, a tuned software,
which was appointed with the same name (i.e. VADASE), was implemented. Ex-
ploiting this software to process a large amount of both simulated and real data,
the main advantages of VADASE, as well as its limitations, were investigated
in details. At a first stage, VADASE effectiveness was proven on a simulated
example. First, a known displacement (1 cm East and North and 2 cm Up) was
synthetically introduced into carrier phase observations collected at 1 Hz rate by
the M0SE permanent GPS station (Rome, Italy). Then, these data were pro-
cessed using the variometric algorithm: the displacements were estimated with
an accuracy of 1 ÷ 2 mm in the horizontal and the vertical directions. The solu-
tions obtained using the GPS broadcast products available in real-time and the
best quality products supplied by International GNSS Service (IGS) a posteriori
displayed a global agreement of 1 mm for the horizontal components and 2 mm
for the height.
Given this fundamental proof of success, and provided that the variometric
algorithm was originally conceived to contribute in the field of GPS seismology
and tsunami warning systems, VADASE was applied to retrieve the coseismic dis-
placements and the waveforms generated by real earthquakes. Here, it is worth
underlining that all VADASE results were obtained using exclusively broadcast
products that are available in real-time. The most significant outcomes were ob-
tained by considering data collected at 1 Hz rate from the IGS station of BREW
during the Denali Fault, Alaska earthquake (Mw 7.9, November 3, 2002), at 10
Hz rate from CADO station during the L’Aquila earthquake (Mw 6.3, April 6,
2009), and at 5 Hz rate from some stations included in the University NAVSTAR
Consortium (UNAVCO)-Plate Boundary Observatory (PBO) network during the
Baja, California earthquake (Mw 7.2, April 4, 2010). In all cases, the agreement
between VADASE and other solutions achieved by different research groups em-
ploying different methodologies was between few centimeters and a couple of
decimeters.
The real-time potentialities of the variometric approach were internationally
recognized during the recent tremendous earthquake in Japan (Mw = 9.0, March
11, 2011), when the GNSS research team of “Sapienza” University of Rome was
able to provide the first waveforms results among the scientific community. The
results obtained for IGS stations of MIZU, USUD and from EV-network station
JA01 were compared with those stemming from the PPP approach implemented
in the software developed at Natural Resources Canada (NRCan) [62]1. The
agreement between VADASE and PPP was evaluated in terms of the Root Mean
Square Error (RMSE) of the differences. In addition, it was investigated the
agreement reliance with the earthquake duration. The RMSE of the differences
between the two solutions ranged from 0.01 ÷ 0.02 m in East and North and
0.06 m in Up, after one minute, to approximately 0.05 m in East and North
and (with much larger variability) 0.20 m in Up after four minutes. Further,
the agreement between the two approaches evaluated in terms of peak to peak
displacements appeared to be independent from the earthquake duration. In de-
tails, the differences reached approximately 0.01 m in East and North and 0.03 m
in Up components. Finally, the correlation coefficient between the two solutions
proved to be higher than 99% for the planimetric components (but for the East
component of USUD and the North component of JA01 which showed 97% and
96% correlations, respectively). The vertical component showed slightly lower
(and with larger variability) correlations: 65%, 84% and 90% for stations MIZU,
USUD and JA01, respectively.
At the moment of this writing, VADASE is subject of a pending patent of the
“Sapienza” University of Rome ever since June 2010. In October 2010 VADASE
was recognized as a simple and effective approach towards real-time coseismic
displacement waveform estimation and it was awarded the German Aerospace
Agency (DLR) Special Topic Prize and the First Audience Award in the European
Satellite Navigation Competition (ESNC) 2010
Variometric approach for real-time GNSS navigation: First demonstration of Kin-VADASE capabilities
No full textThe use of Global Navigation Satellite Systems (GNSS) kinematic positioning for navigational applications dramatically increased over the last decade. Real-time high performance navigation (positioning accuracy from one to few centimeters) can be achieved with established techniques such as Real Time Kinematic (RTK), and Precise Point Positioning (PPP). Despite their potential, the application of these techniques is limited mainly by their high cost. This work proposes the Kinematic implementation of the Variometric Approach for Displacement Analysis Standalone Engine (Kin-VADASE) and gives a demonstration of its performances in the field of GNSS navigation. VADASE is a methodology for the real-time detection of a standalone GNSS receiver displacements. It was originally designed for seismology and monitoring applications, where the receiver is supposed to move for few minutes, in the range of few meters, around a predefined position. Kin-VADASE overcomes the aforementioned limitations and aims to be a complete methodology with fully kinematic capabilities. Here, for the first time, we present its application to two test cases in order to estimate high rate (i.e., 10 Hz) kinematic parameters of moving vehicles. In this demonstration, data are collected and processed in the office, but the same results can be obtained in real-time through the implementation of Kin-VADASE in the firmware of a GNSS receiver. All the Kin-VADASE processing were carried out using double and single frequency observations in order to investigate the potentialities of the software with geodetic class and low-cost single frequency receivers. Root Mean Square Errors in 3D with respect to differential positioning are at the level of 50 cm for dual frequency and better than 1 meter for single frequency data. This reveals how Kin-VADASE features the main advantage of the standalone approach and the single frequency capability and, although with slightly lower accuracy with respect to the established techniques, can be a valid alternative to estimate kinematic parameters of vehicle in motions
SISTEMA DI MISURA DI MOVIMENTI IN TEMPO REALE, IN PARTICOLARE DI MOVIMENTI COSISMICI E DI VIBRAZIONI DI STRUTTURE
No full textGlobal and local reference frames
No full textThe goal of this review paper is to recall the concept of geodetic reference frame, showing its intrinsic dependence from all the information and choices related to its realization, and to discuss the still alive distinction between "global'' and "local'' reference frames, considering the unbreakable link between Geodesy and Geophysics. An up-to-date review of the most relevant presently adopted global and local (in this respect, mainly at European and Italian level) reference frames is presented. Finally, some conclusions and still open problems, related to the current research, are outlined
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