Using electromagnetic methods to map and delineate high-grade harzburgite pods within the Ni-Cu mineralised Jacomynspan ultramafic sill, Northen Cape, South Africa

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016.The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion

The Impact of Acoustic Imaging Geometry on the Fidelity of Seabed Bathymetric Models

Attributes derived from digital bathymetric models (DBM) are a powerful means of analyzing seabed characteristics. Those models however are inherently constrained by the method of seabed sampling. Most bathymetric models are derived by collating a number of discrete corridors of multibeam sonar data. Within each corridor the data are collected over a wide range of distances, azimuths and elevation angles and thus the quality varies significantly. That variability therefore becomes imprinted into the DBM. Subsequent users of the DBM, unfamiliar with the original acquisition geometry, may potentially misinterpret such variability as attributes of the seabed. This paper examines the impact on accuracy and resolution of the resultant derived model as a function of the imaging geometry. This can be broken down into the range, angle, azimuth, density and overlap attributes. These attributes in turn are impacted by the sonar configuration including beam widths, beam spacing, bottom detection algorithms, stabilization strategies, platform speed and stability. Superimposed over the imaging geometry are residual effects due to imperfect integration of ancillary sensors. As the platform (normally a surface vessel), is moving with characteristic motions resulting from the ocean wave spectrum, periodic residuals in the seafloor can become imprinted that may again be misinterpreted as geomorphological information

Magnetometry with nitrogen-vacancy defects in diamond

The isolated electronic spin system of the Nitrogen-Vacancy (NV) centre in diamond offers unique possibilities to be employed as a nanoscale sensor for detection and imaging of weak magnetic fields. Magnetic imaging with nanometric resolution and field detection capabilities in the nanotesla range are enabled by the atomic-size and exceptionally long spin-coherence times of this naturally occurring defect. The exciting perspectives that ensue from these characteristics have triggered vivid experimental activities in the emerging field of "NV magnetometry". It is the purpose of this article to review the recent progress in high-sensitivity nanoscale NV magnetometry, generate an overview of the most pertinent results of the last years and highlight perspectives for future developments. We will present the physical principles that allow for magnetic field detection with NV centres and discuss first applications of NV magnetometers that have been demonstrated in the context of nano magnetism, mesoscopic physics and the life sciences.Comment: Review article, 28 pages, 16 figure

High resolution radargrammetry with COSMO-SkyMed, TerraSAR-X and RADARSAT-2 imagery: development and implementation of an image orientation model for Digital Surface Model generation

Digital Surface and Terrain Models (DSM/DTM) have large relevance in several territorial applications, such as topographic mapping, monitoring engineering, geology, security, land planning and management of Earth's resources. The satellite remote sensing data offer the opportunity to have continuous observation of Earth's surface for territorial application, with short acquisition and revisit times. Meeting these requirements, the SAR (Synthetic Aperture Radar) high resolution satellite imagery could offer night-and-day and all-weather functionality (clouds, haze and rain penetration). Two different methods may be used in order to generate DSMs from SAR data: the interferometric and the radargrammetric approaches. The radargrammetry uses only the intensity information of the SAR images and reconstructs the 3D information starting from a couple of images similarly to photogrammetry. Radargrammetric DSM extraction procedure consists of two basic steps: the stereo pair orientation and the image matching for the automatic detection of homologous points. The goal of this work is the definition and the implementation of a geometric model in order to orientate SAR imagery in zero Doppler geometry. The radargrammetric model implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione - developed at the Geodesy and Geomatic Division - University of Rome "La Sapienza") is based on the equation of radar target acquisition and zero Doppler focalization Moreover a tool for the SAR Rational Polynomial Coefficients (RPCs) generation has been implemented in SISAR software, similarly to the one already developed for the optical sensors. The possibility to generate SAR RPCs starting from a radargrammetric model sounds of particular interest since, at present, the most part of SAR imagery is not supplied with RPCs, although the RPFs model is available in several commercial software. Only RADARSAT-2 data are supplied with vendors RPCs. To test the effectiveness of the implemented RPCs generation tool and the SISAR radargrammetric orientation model the reference results were computed: the stereo pairs were orientated with the two model. The tests were carried out on several test site using COSMO-SkyMed, TerraSAR-X and RADARSAT-2 data. Moreover, to evaluate the advantages and the different accuracy between the orientation models computed without GCPs and the orientation model with GCPs a Monte Carlo test was computed. At last, to define the real effectiveness of radargrammetric technique for DSM extraction and to compare the radrgrammetric tool implemented in a commercial software PCI-Geomatica v. 2012 and SISAR software, the images acquired on Beauport test site were used for DSM extraction. It is important underline that several test were computed. Part of this tests were carried out under the supervision of Prof. Thierry Toutin at CCRS (Canada Centre of Remote Sensing) where the PCI-Geomatica orientation model was developed, in order to check the better parameters solution to extract radargrammetric DSMs. In conclusion, the results obtained are representative of the geometric potentialities of SAR stereo pairs as regards 3D surface reconstruction

Advanced perception, navigation and planning for autonomous in-water ship hull inspection

Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent operations on naval ships.United States. Office of Naval Research (Grant N00014-06-10043)United States. Office of Naval Research (Grant N00014-07-1-0791

Vision Sensors and Edge Detection

Vision Sensors and Edge Detection book reflects a selection of recent developments within the area of vision sensors and edge detection. There are two sections in this book. The first section presents vision sensors with applications to panoramic vision sensors, wireless vision sensors, and automated vision sensor inspection, and the second one shows image processing techniques, such as, image measurements, image transformations, filtering, and parallel computing

A Novel Biosensor Using Nanolithographically-Produced Submicron Optical Sources for the Study of Cell Adhesion and Chemotaxis

Cell adhesion and chemotaxis are two key factors determining cell behaviour and differentiation which are currently analysed by microscopic examination of the cell or membrane-associated fluorescence labels. These analyses are often slow, labour intensive and of limited informational content. This thesis describes the physical theory and experimental aspects of an optical method suitable for monitoring cell contact, adhesion to a surface and chemotaxis beyond the conventional limit of optical microscopy by means of a device that utilises both a plain bare surface and arrays of apertures nanolithographically-produced in the surface of a Surface Plasmon Resonance (SPR) sensor structure. Any minute vertical movement of the cell, within the near-field of the SPR active surface or actual cell/surface contact, creates intensity fluctuations, detectable in the far-field. This was demonstrated during experiments with non-apertured devices. (A video demonstrating the biological features of the device accompanies this thesis and may be obtained by contacting University of Plymouth's LRC.) The light scattered by each nanolithographically-produced aperture also fluctuates as a consequence of the cell approaching to within a few hundred nanometres of the aperture bearing surface and demonstrated detection of minute vertical movement on the surface of the apertured device. The combination of apertured and non-apertured detection results in a highly spatially-sensitive 3-dimensional sensor. Digitising the output from a CCD camera allows patterns of intensity fluctuation to be correlated with the contact and adhesion of individual cells on the active surface over a short period of time (2-3 minutes). Initial trials of an apertured device (diameter (^) « wavelength of incident light ( X ) ) carried out by our collaborating partners Drs R. Carr and S. Al-shukri at the Centre for Applied Microbiology and Research, Porton Down demonstrated that the use of apertures etched in a SPR metal surface produced a highly sensitive dielectric monitor, i.e. sensitive to very small changes in the refractive index of the micro-environment adjacent to the aperture. This was proposed as being of potentially great value in the development of extremely sensitive probes of dielectric particulates of sub-micron dimensions, i.e. biological macromolecules and supramolecular structures. Characterisation of the associated radiative and non-radiative evanescent fields on the surface of the device was conducted in order to gain a greater knowledge of the mechanisms by which the interactions between the cells adjacent to and in direct contact with the apertures and evanescent fields produced such significant intensity fluctuations in the results at CAMR. A combinational Scanning Probe Microscope was developed and used in Scanning Nearfield Optical Microscope and Photon Scanning Tunnelling Microscope modes of operation to detect the evanescent and radiative fields respectively. Detailed mapping of the radiative pattern in the near-field of the large apertures {<p » X) demonstrated a diffraction of approximately 25% of the Surface Plasmon Wave (SPW) either side of the centre of the aperture with the remainder being contained within the metal layer. Scattering at the second aperture interface, i.e. air/metal, was shown to be of a lower magnitude as a result of non-surface plasmon enhancement within the non-resonant aperture. Characterisation of the intensity profile of small apertures (^ < A) was beyond the scope of this project due to its limited time and finance and was not undertaken. A section in the conclusions is dedicated to giving a possible cause of the intensity profiles IV detected during the initial studies at CAMR with possible procedures required to verify and expand such work. In order to investigate the potential of the device in the biological environment, biological trials were carried out with collaborating establishments at Salisbury and Exeter and demonstrated that this dual sensing microscopic technique had great potential in the 3-dimensional monitoring of cell movement together with the capability of extending our knowledge of cell behaviour with the view to a system of rapid screening for tumour cells. This technique has produced real-time images of cell behaviour, which to our knowledge has not been previously seen before by any other microscopy technique. The finding of these trials are documented in this thesis with possible theories as to what the biological effects responsible for these results may possibly be. Future work into the verification of these effects and more biological trials and procedures are described in the hope that afler further work the device may be developed into a commercial and readily available scientific unit for use in the laboratory.FORCE Cancer Research Centre, Exeter and Centre for Applied Microbiology and Research, Porton Dow

Space infrared telescope pointing control system. Infrared telescope tracking in the presence of target motion

The use of charge-coupled-devices, or CCD's, has been documented by a number of sources as an effective means of providing a measurement of spacecraft attitude with respect to the stars. A method exists of defocussing and interpolation of the resulting shape of a star image over a small subsection of a large CCD array. This yields an increase in the accuracy of the device by better than an order of magnitude over the case when the star image is focussed upon a single CCD pixel. This research examines the effect that image motion has upon the overall precision of this star sensor when applied to an orbiting infrared observatory. While CCD's collect energy within the visible spectrum of light, the targets of scientific interest may well have no appreciable visible emissions. Image motion has the effect of smearing the image of the star in the direction of motion during a particular sampling interval. The presence of image motion is incorporated into a Kalman filter for the system, and it is shown that the addition of a gyro command term is adequate to compensate for the effect of image motion in the measurement. The updated gyro model is included in this analysis, but has natural frequencies faster than the projected star tracker sample rate for dim stars. The system state equations are reduced by modelling gyro drift as a white noise process. There exists a tradeoff in selected star tracker sample time between the CCD, which has improved noise characteristics as sample time increases, and the gyro, which will potentially drift further between long attitude updates. A sample time which minimizes pointing estimation error exists for the random drift gyro model as well as for a random walk gyro model

Resolution improvement methods applied to digital holography

This thesis discusses the creation, acquisition and processing of digital holograms. Several techniques to improve the optical resolution have been investigated and developed. The optical resolution of numerically reconstructed digital holograms is restricted by both the sampling frequency and the overall sensor-size of the digital camera chip used. This thesis explores the limitations on the optical resolution of the holograms obtained. A typical sensor-size and sampling frequency for digital holograms is 10 mm and 100 lp/mm, respectively, whereas holographic plates used for optical holography can be more than a meter in size and have a sampling frequency of 3000 lp/mm. In order to take full advantage of the benefits digital holography offers, such as fast image acquisition and direct phase accessibility, the problem of reduced resolution needs to be overcome. Three resolution improvement methods have been developed in the scope of this PhD thesis. Prior to implementing the resolution improvement methods, different holographic setups have been analyzed, using the Space-bandwidth product (SBP) to calculate the information distribution both in the recording and reconstruction process. The first resolution improvement method is based on the synthetic aperture method. In this manner an increased sensor area can be obtained resulting in a larger numerical aperture (NA). A larger NA enables a more detailed reconstruction. The problem encountered in doing this is that an increased optical resolution results in a smaller depth of field. This has been overcome in this thesis by applying the extended depth of field method. As a result a high resolution in focus reconstruction of all longitudinal object regions is obtained. Moreover, the extended depth of field method allows a topological mapping of the object. The second resolution improvement method is based on sampling the interference pattern with sub-pixel accuracy. This was carried out on a CMOS-sensor and implemented by moving the light sensitive pixel-area into the dead zone in a 4x4 grid to cover whole the pixel-area. As a result the sensor's sampling frequency is doubled. The increased sampling frequency permits a reduction of the recording distance which results in an increased optical resolution of the reconstructed hologram. The third and novel approach described in this thesis has been to increase the optical resolution stored in a digital hologram by the combination of the synthetic aperture and the sub-pixel sampling methodBy analogy with the Fresnel-. The resolution improvement methods have been demonstrated both for lens-less digital holography and digital holographic microscopy