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    ABSTRACT: Correlation matching has been widely accepted as a rudimentary similarity measure to obtain dense 3D reconstruction from a stereo pair. In particular, given a large overlapping area between images with minimal scale differences, the correlation results followed by a geometrically constrained global optimisation delivers adequately dense and accurate reconstruction results. In order to achieve greater reliability, however, correlation matching should correctly account for the geometrical distortion introduced by the different viewing angles of the stereo or multi-view sensors. Conventional adaptive least squares correlation (ALSC) matching addresses this by modifying the shape of a matching window iteratively, assuming that the distortion can be approximated by an affine transform. Nevertheless, since an image captured from different viewing angle is often not practically identical due to scene occlusions, the matching confidence normally deteriorates. Subsequently, it affects the density of the reconstruction results from ALSC-based stereo region growing algorithms. To address this, we propose an advanced ALSC matching method that can progressively update matching weight for each pixel in an aggregating window using a relaxation labelling technique. The experimental results show that the proposed method can improve matching performance, which consequently enhances the quality of stereo reconstruction. Also, the results demonstrate its ability to refine a scale invariant conjugate point pair to an affine and scale invariant point pair.
    Pattern Recognition. 10/2012; 45(10):3795–3809.
  • Department of Space and Climate Physics, University College London, 01/2011, Degree: Masters (group), Supervisor: Dr. David Williams
  • Department of Space and Climate Physics, University College London, 01/2011, Degree: Masters, Supervisor: Jan-Peter Muller
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    ABSTRACT: The kinematics of stars and planetary nebulae in early-type galaxies provide vital clues to the enigmatic physics of their dark matter haloes. We fit published data for 14 such galaxies using a spherical, self-gravitating model with two components: (i) a Sérsic stellar profile fixed according to photometric parameters, and (ii) a polytropic dark matter halo that conforms consistently to the shared gravitational potential. The polytropic equation of state can describe extended theories of dark matter involving self-interaction, non-extensive thermostatistics or boson condensation (in a classical limit). In such models, the flat-cored mass profiles widely observed in disc galaxies are due to innate dark physics, regardless of any baryonic agitation. One of the natural parameters of this scenario is the number of effective thermal degrees of freedom of dark matter (Fd) which is proportional to the dark heat capacity. By default, we assume a cosmic ratio of baryonic and dark mass. Non-Sérsic kinematic ideosyncrasies and possible non-sphericity thwart fitting in some cases. In all 14 galaxies, the fit with a polytropic dark halo improves or at least gives similar fits to the velocity dispersion profile, compared to a stars-only model. The good halo fits usually prefer Fd values from six to eight. This range complements the recently inferred limit of 7 < Fd < 10, derived from constraints on galaxy cluster core radii and black hole masses. However, a degeneracy remains: radial orbital anisotropy or a depleted dark mass fraction could shift our models' preference towards lower Fd; whereas a loss of baryons would favour higher Fd.
    Monthly Notices of the Royal Astronomical Society 06/2010; 405(1):77 - 90.
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    ABSTRACT: The acquisition of high resolution topographic data such as Digital Terrain Models (DTMs) and orthoimages from various Martian stereo imagery is now readily available. The very successful European Space Agency (ESA) Mars Express mission includes the High Resolution Stereo Camera (HRSC) which has provided, since March 2004, an increasingly global set of along-track stereo coverage at relatively high spatial resolution (<100 m, mainly 12.5–25 m) over the Martian surface. Previous DTM generation was only accomplished with planned or serendipitous Viking Orbiter and more recently from Mars Orbiter Camera Narrow Angle (MOC-NA) stereo-pairs. Neither system was designed for stereo photogrammetric DTM generation. Recently, the NASA Mars Reconnaissance Orbiter (MRO) deployed two major optical pushbroom CCD cameras which are capable of across-track stereo targeting. Both Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) provide very high resolution stereo imagery at 6 m and submetre, respectively. A stereo processing chain has been developed which uses a non-rigorous sensor model with geodetic control derived from a reference stereo data source (HRSC) and is here shown to be successfully applied to CTX and HiRISE stereo imagery for 3 test areas. This processing chain is here demonstrated to generate excellent quality DTMs (up to a maximum grid spacing of 0.7 m with HiRISE and 10 m with CTX) and associated ortho images. The photogrammetric quality of these products is here verified using inter-comparisons with HRSC and Mars Orbiter Laser Altimeter (MOLA) data sets and shows good agreement.
    Planetary and Space Science 12/2009; 57(14-15):2095–2112.
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    ABSTRACT: The complex structure of the light curves of Swift Gamma-Ray Bursts (GRBs) has made the identification of breaks, and the interpretation of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to identify breaks, which are possibly hidden, and to constrain the blast wave parameters; electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so by comparing the observed multiwavelength light curves and X-ray spectra of our sample to the predictions of the blast wave model. We can successfully interpret all of the bursts in our sample of 10, except two, within this framework and we can estimate, with confidence, the electron energy distribution index for 6 of the sample. Furthermore, we identify jet breaks in a number of the bursts. A statistical analysis of the distribution of p reveals that, even in the most conservative case of least scatter, the values are not consistent with a single, universal value. The values of k suggest that the circumburst density profiles are not drawn from only one of the constant density or wind-like media populations.
    Monthly Notices of the Royal Astronomical Society 04/2009; 395(1):580 - 592.
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    ABSTRACT: As any comet nears the Sun, gas sublimes from the nucleus taking dust with it. Jupiter family comets are no exception. The neutral gas becomes ionized, and the interaction of a comet with the solar wind starts with ion pickup. This key process is also important in other solar system contexts wherever neutral particles become ionized and injected into a flowing plasma such as at Mars, Venus, Io, Titan and interstellar neutrals in the solar wind. At comets, ion pickup removes momentum and energy from the solar wind and puts it into cometary particles, which are then thermalised via plasma waves. Here we review what comets have shown us about how this process operates, and briefly look at how this can be applied in other contexts. We review the processes of pitch angle and energy scattering of the pickup ions, and the boundaries and regions in the comet–solar wind interaction. We use in-situ measurements from the four comets visited to date by spacecraft carrying plasma instrumentation: 21P/Giacobini-Zinner, 1P/Halley, 26P/Grigg-Skjellerup and 19P/Borrelly, to illustrate the process in action. While, of these, comet Halley is not a Jupiter class comet, it has told us the most about cometary plasma environments. The other comets, which are from the Jupiter family, give an interesting comparison as they have lower gas production rates and less-developed interactions. We examine the prospects for Rosetta at comet Churyumov-Gerasimenko, another Jupiter family comet where a wide range of gas production rates will be studied.
    Planetary and Space Science 01/2009;
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    ABSTRACT: Atlantic hurricane activity has increased significantly since 1995 (refs 1-4), but the underlying causes of this increase remain uncertain. It is widely thought that rising Atlantic sea surface temperatures have had a role in this, but the magnitude of this contribution is not known. Here we quantify this contribution for storms that formed in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico; these regions together account for most of the hurricanes that make landfall in the United States. We show that a statistical model based on two environmental variables--local sea surface temperature and an atmospheric wind field--can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005. We then remove the influence of the atmospheric wind field to assess the contribution of sea surface temperature. Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August-September sea surface temperature over the period we consider is such that a 0.5 degrees C increase in sea surface temperature is associated with a approximately 40% increase in hurricane frequency and activity. The results also indicate that local sea surface warming was responsible for approximately 40% of the increase in hurricane activity relative to the 1950-2000 average between 1996 and 2005. Our analysis does not identify whether warming induced by greenhouse gases contributed to the increase in hurricane activity, but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperature will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity.
    Nature 02/2008; 451(7178):557-60.
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    ABSTRACT: The accuracy and spatial resolutions of modern planetary mapping missions are being rapidly improved by more sophisticated sensors and tracking systems. Especially for Mars, orbital cameras such as MOC, THEMIS and HRSC are providing optical imagery up-to 10-20 metres or even a few metres' resolutions. Moreover the capability of stereo imaging of HRSC and MOC-NA make it feasible to extract a relatively high resolution DEM (Digital Elevation Model) for geological and geo-morphological research. However, even with HRSC which has 12.5 m spatial resolution, the quality of reconstructed 3D Martian surfaces is still not suitable for several purposes such as landing site survey, local roughness extraction and small structure observations. The successful deployment of the NASA MRO with the 30cm HiRISE has dramatically upgraded the resolution limit of Martian surface observation for the targets, many of which have never been observed by other optical sensors before. The difficulty in fully exploiting the potential of HiRISE is that the tracking information which is indispensable for sensor modeling and stereo 3D data extraction, is not yet available at a sufficiently high accuracy. Therefore photogrammetrically well controlled stereo or monocular mapping by HiRISE has only been performed by a few teams who can fully access and update all sensor and navigation data (Heyd et al., 2007 LPSC, Kirk et al., 2007 ISPRS WG IV/7 Workshop). We have developed a simple generic mapping method for HIRISE stereo imagery and applied this to a stereo pair in the Eberswalde Delta which is publicly available. Without any detailed tracking information and sensor specification, it produce what appears to be a very reasonable quality set of mapping products including a 2.5m resolution stereo DTM and a 30cm orthoimage which is controlled up to 30-40m horizontal accuracy when compared with a bundle-adjusted HRSC image. The theory of this method is based on a non-rigorous sensor model employing HRSC intersection points as the control information [3] (Kim et al., 2007) which also exploits epi-polarity. For more reliable horizontal and vertical control, the quality of the HRSC intersection point was optimized by employing a sophisticated image matching and bundle adjusted orientation information for HRSC which was kindly provided by U of Hannover. By creating epi-polar rectified images of HiRISE and then applying a non-rigorous sensor model, the degrees of freedom of the geospatial coordinates were reduced and the relative coordinate was easily converted into a Mars mapping coordinate system. In addition, using image matching with epi-polar rectified image pair provided more reliable disparity values. The constructed DTM is well correlated with the geo-morphological features, which is observed in the optical image. However, a current unknown with this method is that it is still not clear whether stereo intersections of HRSC image can provided sufficient vertical accuracy to project relative disparity into ellipsoidal heights. We suggest that we could use this method as a temporary mapping aid to an eventual rigorous mapping of HiRISE. Over the areas which have been acquired using HiRISE stereo scenes, this method is being tested and evaluations perform to compare against HSRC products.
    07/2007; -1:442.
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    ABSTRACT: Soft gamma-ray repeaters (SGRs) are a peculiar family of bursting neutron stars that, occasionally, have been observed to emit extremely energetic giant flares (GFs), with energy release up to approximately 10(47) ergs(-1). These are exceptional and rare events. It has been recently proposed that GFs, if emitted by extragalactic SGRs, may appear at Earth as short gamma-ray bursts. Here, I will discuss the properties of the GFs observed in SGRs, with particular emphasis on the spectacular event registered from SGR 1806-20 in December 2004. I will review the current scenario for the production of the flare, within the magnetar model, and the observational implications.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 06/2007; 365(1854):1307-13.
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