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  1. 1 point
    Interesting articles : North-South displacement field - 1999 Hector-Mine earthquake, California In complement to seismological records, the knowledge of the ruptured fault geometry and co-seismic ground displacements are key data to investigate the mechanics of seismic rupture. This information can be retrieved from sub-pixel correlation of optical images. We are investigating the use of SPOT (Satellite pour l'Observation de la Terre) satellites images. The technique developed here is attractive due to the operational status of a number of optical imaging programs and the availability of archived data. However, uncertainties on the imaging system itself and on its attitude dramatically limit its potential. We overcome these limitations by applying an iterative corrective process allowing for precise image registration that takes advantage of the availability of accurate Digital Elevation Models with global coverage (SRTM). This technique is thus a valuable complement to SAR interferometry which provides accurate measurements kilometers away from the fault but generally fails in the near-fault zone where the fringes get noisy and saturated. Comparison between the two methods is briefly discussed, with application on the 1992 Landers earthquake in California (Mw 7.3). Applications of this newly developped technique are presented: the horizontal co-seismic displacement fields induced by the 1999 Hector-Mine earthquake in California (Mw 7.1) and by the 1999 Chichi earthquake in Taiwan (Mw 7.5) have recently been retrieved using archive images. Data obtained can be downloaded (see further down) Latest Study Cases Sub-pixel correlation of optical images Following is the flow chart of the technique that as been developped. It allows for precise orthorectification and coregistration of the SPOT images. More details about the optimization process will be given in the next sections. Understanding the disparities measured from Optical Images Differences in geometry between the two images to be registered: - Uncertainties on attitudes parameters (roll, pitch, yaw) - Inaccuracy on orbital parameters (position, velocity) - Incidence angle differences + topography uncertainties (parallax effect) - Optical and Electronic biases (optical aberrations, CCD misalignment, focal length, sampling period, etc… ) » May account for disparities up to 800 m on SPOT 1,2,3,4 images; 50m for SPOT 5 (see [3]). Ground deformations: - Earthquakes, land slides, etc… » Typically subpixel scale: ranging from 0 to 10 meters. Temporal decorrelation: - Changes in vegetation, rivers, changes in urban areas, etc… » Correlation is lost: add noise to the measurement – up to 1m. » Ground deformations are largely dominated by the geometrical artifacts. Precise registration: geometrical corrections SPOT (Systeme pour l'Observation de la Terre) satellites are pushbroom imaging systems ([1],[2]): all optical parts remain fixed during acquisition and the scanning is accomplished by the forward motion of the spacecraft. Each line in the image is then acquired at a different time and submitted to the different variations of the platform. The orthorectification process consists in modeling and correcting these variations to produce cartographic distortion free images. It is then possible to accurately register images and look for their disparities using correlation techniques. Attitude variations (roll, pitch, and yaw) during the scanning process have to be integrated in the image model (see [1],[2]). Errors in correcting the satellite look directions will result in projecting the image pixels at the wrong location on the ground: important parallax artifacts will be seen when measuring displacement between two images. Exact pixel projection on the ground is achieved through an optimization algorithm that iteratively corrects the look directions by selecting ground control points. An accurate topography model has to be used. What parameters to optimize? - Initial attitudes values of the platform (roll, pitch, yaw), - Constant drift of the attitude values along the image acquisition, - Focal length (different value depending on the instrument , HRG1 – HRG2), - Position and velocity. How to optimize: Iterative algorithm using a set of GCPs (Ground Control Points). GCPs are generated automatically with a subpixel accuracy: they result from a correlation between an orthorectified reference frame and the rectified image whose parameters are to be optimized. A two stages procedure: - One of the image is optimized with respect to the shaded DEM (GCP are generated from the correlation with the shaded DEM). The DEM is then considered as the ground truth. No GPS points are needed. - The other image is then optimized using another set of GCP resulting from the correlation with the first image (co-registration). Measuring co-seismic deformation with InSAR, a comparison A fringe represents a near-vertical displacement of 2.8 cm SAR interferogram (ERS): near-vertical component of the ground displacement induced by the 1992 Landers earthquake [Massonnet et al., 1993]. No organized fringes in a band within 5-10 km of the fault trace: displacement sufficiently large that the change in range across a radar pixel exceeds one fringe per pixel, coherence is lost. http://earth.esa.int/applications/data_util/ndis/equake/land2.htm » SAR interferometry is not a suitable technique to measure near fault displacements The 1992 Landers earthquake revisited: Profile in offsets and elastic modeling show good agreement From: [6] - Measuring earthqakes from optical satellite images, Van Puymbroeck, Michel, Binet, Avouac, Taboury - Applied Optics Vol. 39, No 20, 10 July 2000 Other applications of the technique, see [4], [5]. » Fault ruptures can be imaged from this technique Applying the precise rectification algorithm + subpixel correlation: The 1999 Hector-Mine earthquake (Mw 7.1, California) Obtaining the Data (available in ENVI file Format. Load banbs as gray scale images. Bands are: N/S offsets, E/W offsets, SNR): Raw and filtered results: HectorMine.zip Pre-earthquake image: SPOT 4, acquisition date: 08-17-1998 Ground resolution: 10m Post-earthquake image: SPOT 2, acquisition date: 08-18-2000 Ground resolution: 10m Offsets measured from correlation: Correspond to sub-pixel offsets in the raw images. Correlation windows: 32 x 32 pixels 96m between two measurements So far we have: - A precise mapping of the rupture zone: the offsets field have a resolution of 96 m, - Measurements with a subpixel accuracy (displacement of at most 10 meters), - Improved the global georeferencing of the images with no GPS measurements, - Improved the processing time since the GCP selection is automatic, - Suppressed the main attitude artifacts. The profiles do not show any long wavelength deformations (See Dominguez et al. 2003) We notice: - Linear artifacts in the along track direction due to CCD misalignments, Schematic of a DIVOLI showing four CCD linear arrays. - Some topographic artifacts: the image resolution is higher than the DEM one, - Several decorrelations due to rivers and clouds, - High frequency noise due to the noise sensitivity of the Fourier correlator (See Van Puymbroeck et al.). Conclusion Subpixel correlation technique has been improved to overcome most of its limitations: » Precise rectification and co-registration of the images, » No more topographic effects (depending on the DEM resolution), » No need for GPS points – independent and automatic algorithm, » Better spatial resolution (See Van Puymbroeck et al.) To be improved: » Stripes due to the CCD’s misalignment, » high frequency noise from the correlator, » Process images with corrupted telemetry. » The subpixel correlation technique appears to be a valuable complement to SAR interferometry for ground deformation measurements. References: [1] SPOT 5 geometry handbook: ftp://ftp.spot.com/outgoing/SPOT_docs/geometry_handbook/S-NT-73-12-SI.pdf [2] SPOT User's Handbook Volume 1 - Reference Manual: ftp://ftp.spot.com/outgoing/SPOT_docs/SPOT_User's Handbook/SUHV1RM.PDF [3] SPOT 5 Technical Summary ftp://ftp.spot.com/outgoing/SPOT_docs/technical/spot5_tech_slides.ppt [4] Dominguez S., J.P. Avouac, R. Michel Horizontal co-seismic deformation of the 1999 Chi-Chi earthquake measured from SPOT satellite images: implications for the seismic cycle along the western foothills of Central Taiwan, J. Geophys. Res., 107, 10 1029/2001JB00482, 2003. [5] Michel, R. et J.P., Avouac, Deformation due to the 17 August Izmit earthquake measured from SPOT images, J. Geophys. Res., 107, 10 1029/2000JB000102, 2002. [6] Van Puymbroeck, N., Michel, R., Binet, R., Avouac, J.P. and Taboury, J. Measuring earthquakes from optical satellite images, Applied Optics Information Processing, 39, 23, 3486–3494, 2000. Publications: Leprince S., Barbot S., Ayoub F., Avouac, J.P. Automatic, Precise, Ortho-rectification and Co-registration for Satellite Image Correlation, Application to Seismotectonics. To be submitted. Conferences: F Levy, Y Hsu, M Simons, S Leprince, J Avouac. Distribution of coseismic slip for the 1999 ChiChi Taiwan earthquake: New data and implications of varying 3D fault geometry. AGU 2005 Fall meeting, San Francisco. M Taylor, S Leprince, J Avouac. A Study of the 2002 Denali Co-seismic Displacement Using SPOT Horizontal Offsets, Field Measurements, and Aerial Photographs. AGU 2005 Fall meeting, San Francisco. Y Kuo, F Ayoub, J Avouac, S Leprince, Y Chen, J H Shyu, Y Kuo. Co-seismic Horizontal Ground Slips of 1999 Chi-Chi Earthquake (Mw 7.6) Deduced From Image-Comparison of Satellite SPOT and Aerial Photos. AGU 2005 Fall meeting, San Francisco. source: http://www.tectonics.caltech.edu/geq/spot_coseis/
  2. 1 point
    please elaborate, what do you plan on using remote sensing data to make some animation? please add the details simple example for their functions can be see here: http://animove.org/wp-content/uploads/2019/04/Daniel_Palacios_animate_moveVis.html
  3. 1 point
    Google says it has built a computer that is capable of solving problems that classical computers practically cannot. According to a report published in the scientific journal Nature, Google's processor, Sycamore, performed a truly random-number generation in 200 seconds. That same task would take about 10,000 years for a state-of-the-art supercomputer to execute. The achievement marks a major breakthrough in the technology world's decadeslong quest to use quantum mechanics to solve computational problems. Google CEO Sundar Pichai wrote that the company started exploring the possibility of quantum computing in 2006. In classical computers, bits can store information as either a 0 or a 1 in binary notation. Quantum computers use quantum bits, or qubits, which can be both 0 and 1. According to Google, the Sycamore processor uses 53 qubits, which allows for a drastic increase in speed compared with classical computers. The report acknowledges that the processor's practical applications are limited. Google says Sycamore can generate truly random numbers without utilizing pseudo-random formulas that classical computers use. Pichai called the success of Sycamore the "hello world" moment of quantum computing. "With this breakthrough we're now one step closer to applying quantum computing to—for example—design more efficient batteries, create fertilizer using less energy, and figure out what molecules might make effective medicines," Pichai wrote. IBM has pushed back, saying Google hasn't achieved supremacy because "ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity." On its blog, IBM further discusses its objections to the term "quantum supremacy." The authors write that the term is widely misinterpreted. "First because, as we argue above, by its strictest definition the goal has not been met," IBM's blog says. "But more fundamentally, because quantum computers will never reign 'supreme' over classical computers, but will rather work in concert with them, since each have their unique strengths." News of Google's breakthrough has raised concerns among some people, such as presidential hopeful Andrew Yang, who believe quantum computing will render password encryption useless. Theoretical computer science professor Scott Aaronson refuted these claims on his blog, writing that the technology needed to break cryptosystems does not exist yet. The concept of quantum computers holding an advantage over classical computers has dated back to the early 1980s. In 2012, John Preskill, a professor of theoretical physics at Caltech, coined the term "quantum supremacy." source: https://www.npr.org/2019/10/23/772710977/google-claims-to-achieve-quantum-supremacy-ibm-pushes-back
  4. 1 point
    just found this interesting articles on Agisoft forum : source: https://www.agisoft.com/forum/index.php?topic=7851.0
  5. 1 point
    one of my favorite image hosting, , this is their announcement : Rest in Peace TinyPic
  6. 1 point
    Klau Geomatics has released Real-Time Precise Point Positioning (PPP) for aerial mapping and drone positioning that enables 3 to 5 cm initial positioning accuracy, anywhere in the world, without any base station data or network corrections. With this, you Just need to fly your drone at any distance, anywhere. The system allows to navigate with real-time cm level positioning or geotag your mapping photos and Lidar data. You don’t need to think about setting up a base station, finding quality CORS data or setting up an RTK radio link. You don’t need to be in range of a CORS station, you can fly autonomously, in remote areas, long corridors, unlimited range, it just works, giving you centimetre level accuracy, anywhere. Now, with this latest satellite-based positioning technology, 3 to 5cm accuracy can be achieved, anywhere in the world, with no base station. KlauPPP leverages NovAtel’s industry-leading technology to achieve this quantum leap in PPP accuracy. NovAtel PPP and Klau Geomatics hardware/software system is now the simplest, most convenient and accurate positioning system for UAVs and manned aircraft. The bundled solution enables accurate positioning in any published or custom coordinate system and datum. This technology is very applicable to surveying, mapping, navigation and particularly the emerging drone inspection industry, starting to realize that absolute accuracy is essential to analyze change over time in 3D assets. A BVLOS parcel delivery drone can now travel across a country and arrive exactly on it’s landing pad. No range limitations, no base station requirements or radio links. Highly accurate autonomous flight. Large scale enterprise drone companies can deploy their fleet of operators with a simple, mechanical workflow to capture accurate, repeatable data, without the complications of the survey world; of RTK radio links and network connections or logging base station data within a range of each of their many projects. Now they have a simple consistent operation that just works, every time, every location. “Just as Klau Geomatics led the industry from RTK and GCPs to PPK, we now lead the charge to PPP as the next technology for simple, accurate drone operations”, says Rob Klau, Director of Klau Geomatics source : http://geomatics.com.au/
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