Fast Super-resolution with Affine Motion Using an Adaptive Wiener Filter and Its Application to Airborne Imaging

Fast nonuniform interpolation based super-resolution (SR) has traditionally been limited to applications with translational interframe motion. This is in part because such methods are based on an underlying assumption that the warping and blurring components in the observation model commute. For translational motion this is the case, but it is not true in general. This presents a problem for applications such as airborne imaging where translation may be insufficient. Here we present a new Fourier domain analysis to show that, for many image systems, an affine warping model with limited zoom and shear approximately commutes with the point spread function when diffraction effects are modeled. Based on this important result, we present a new fast adaptive Wiener filter (AWF) SR algorithm for non-translational motion and study its performance with affine motion. The fast AWF SR method employs a new smart observation window that allows us to precompute all the needed filter weights for any type of motion without sacrificing much of the full performance of the AWF. We evaluate the proposed algorithm using simulated data and real infrared airborne imagery that contains a thermal resolution target allowing for objective resolution analysis

Vision-based systems for structural deformation measurement: case studies

This is the author accepted manuscript. The final version is available from Thomas Telford (ICE Publishing) via the DOI in this record.Vision-based systems offer a promising way for displacement measurement and receive increased attention in civil structural monitoring. However, the working performance of vision-based systems, especially the measurement accuracy and the robustness to different field conditions is not fully understood. This study reports three cases studies of vision-based monitoring tests including one in a laboratory, one on a short-span bridge and one on a long-span bridge. The tracking accuracy is quantified in laboratory conditions in the range of 0.02 pixel to 0.20 pixel depending on the target patterns as well as the tracking method selected. The measurement performance under several field challenges are investigated including long-range measurement (e.g. camera-to-target distance at 710 m), low-contrast target patterns, changes of target patterns and changes in lighting conditions. Three representative tracking methods for the video processing, i.e. correlation-based template matching, Lucas Kanade (LK) optical flow estimation and scale-invariant feature transform (SIFT) were used for analysis, indicating their advantages and shortcomings for field measurement. One of the main observations in field application is that changes in lighting conditions might cause some low-frequency measurement error that could be misunderstood without the prior knowledge about structural loading conditions

Interferometric Synthetic Aperture Sonar Signal Processing for Autonomous Underwater Vehicles Operating Shallow Water

The goal of the research was to develop best practices for image signal processing method for InSAS systems for bathymetric height determination. Improvements over existing techniques comes from the fusion of Chirp-Scaling a phase preserving beamforming techniques to form a SAS image, an interferometric Vernier method to unwrap the phase; and confirming the direction of arrival with the MUltiple SIgnal Channel (MUSIC) estimation technique. The fusion of Chirp-Scaling, Vernier, and MUSIC lead to the stability in the bathymetric height measurement, and improvements in resolution. This method is computationally faster, and used less memory then existing techniques

Non-contact vision-based deformation monitoring on bridge structures

Information on deformation is an important metric for bridge condition and performance assessment, e.g. identifying abnormal events, calibrating bridge models and estimating load carrying capacities, etc. However, accurate measurement of bridge deformation, especially for long-span bridges remains as a challenging task. The major aim of this research is to develop practical and cost-effective techniques for accurate deformation monitoring on bridge structures. Vision-based systems are taken as the study focus due to a few reasons: low cost, easy installation, desired sample rates, remote and distributed sensing, etc. This research proposes an custom-developed vision-based system for bridge deformation monitoring. The system supports either consumer-grade or professional cameras and incorporates four advanced video tracking methods to adapt to different test situations. The sensing accuracy is firstly quantified in laboratory conditions. The working performance in field testing is evaluated on one short-span and one long-span bridge examples considering several influential factors i.e. long-range sensing, low-contrast target patterns, pattern changes and lighting changes. Through case studies, some suggestions about tracking method selection are summarised for field testing. Possible limitations of vision-based systems are illustrated as well. To overcome observed limitations of vision-based systems, this research further proposes a mixed system combining cameras with accelerometers for accurate deformation measurement. To integrate displacement with acceleration data autonomously, a novel data fusion method based on Kalman filter and maximum likelihood estimation is proposed. Through field test validation, the method is effective for improving displacement accuracy and widening frequency bandwidth. The mixed system based on data fusion is implemented on field testing of a railway bridge considering undesired test conditions (e.g. low-contrast target patterns and camera shake). Analysis results indicate that the system offers higher accuracy than using a camera alone and is viable for bridge influence line estimation. With considerable accuracy and resolution in time and frequency domains, the potential of vision-based measurement for vibration monitoring is investigated. The proposed vision-based system is applied on a cable-stayed footbridge for deck deformation and cable vibration measurement under pedestrian loading. Analysis results indicate that the measured data enables accurate estimation of modal frequencies and could be used to investigate variations of modal frequencies under varying pedestrian loads. The vision-based system in this application is used for multi-point vibration measurement and provides results comparable to those obtained using an array of accelerometers

Unfocused ultrasound waves for manipulating and imaging microbubbles

With unfocused plane/diverging ultrasound waves, the capability of simultaneous sampling on each element of an array transducer has spawned a branch known as high-frame-rate (HFR) ultrasound imaging, whose frame rate can be two orders of magnitude faster than traditional imaging systems. Microbubbles are micron-sized spheres with a heavy gas core that is stabilized by a shell made of lipids, polymers, proteins, or surfactants. They are excellent ultrasound scatters and have been used as ultrasound contrast agents, and more recently researched as a mechanism for targeted drug delivery. With the Ultrasound Array Research Platform II (UARP II), the objective of this thesis was to develop and advance several techniques for manipulating and imaging microbubbles using unfocused ultrasound waves. These techniques were achieved by combining custom transmit/receiving sequencing and advanced signal processing algorithms, holding promise for enhanced diagnostic and therapeutic applications of microbubbles. A method for locally accumulating microbubbles with fast image guidance was first presented. A linear array transducer performed trapping of microbubble populations interleaved with plane wave imaging, through the use of a composite ultrasound pulse sequence. This technique could enhance image-guided targeted drug delivery using microbubbles. A key component of targeted drug delivery using liposome-loaded microbubbles and ultrasound is the ability to track these drug vehicles to guide payload release locally. As a uniquely identifiable emission from microbubbles, the subharmonic signal is of interest for this purpose. The feasibility of subharmonic plane wave imaging of liposome-loaded microbubbles was then proved. The improved subharmonic sensitivity especially at depth compared to their counterpart of bare (unloaded) microbubbles was confirmed. Following plane wave imaging, the combination of diverging ultrasound waves and microbubbles was investigated. The image formation techniques using coherent summation of diverging waves are susceptible to tissue and microbubble motion artefacts, resulting in poor image quality. A correlation-based 2-D motion estimation algorithm was then proposed to perform motion compensation for HFR contrast-enhanced echocardiography (CEE). A triplex cardiac imaging technique, consisting of B mode, contrast mode and 2-D vector flow imaging with a frame rate of 250 Hz was presented. It was shown that the efficacy of coherent diverging wave imaging of the heart is reliant on carefully designed motion compensation algorithms capable of correcting for incoherence between steered diverging-wave transmissions. Finally, comparisons were made between the correlation-based method and one established image registration method for motion compensation. Results show that the proposed correlation-based method outperformed the image registration model for motion compensation in HFR CEE, with the improved image contrast ratio and visibility of geometrical borders both in vitro and in vivo

Design and evaluation of a full-sensitivity tilt scanning interferometry system for displacement field tomography and profilometry

This thesis reports the investigation and further development of a tilt scanning interferometry system for surface profilometry and sub-surface tomographic applications. A new 3D full sensitivity interferometry system extends the work carried out on a previous prototype that was capable of measuring displacement along one lateral plus the axial component. Depth-resolved imaging is achieved by the acquisition of a sequence of 2D interferograms whilst the illumination beam undergoes a constant rate of tilt and full sensitivity displacement is achieved by performing scans from multiple illumination directions. The comparison of phase volumes from two successive series of scans enables 3D displacement fields to be determined. The working principle that describes the technique is presented, covering the reconstruction of a depth-resolved sample from the detected intensity distribution. The system performance is studied, including measurement repeatability and factors that affect the depth resolution and depth range. Depth resolution is fundamentally limited by the range of the illumination tilting angle and the new system design enables a larger range. However, the resolution is degraded by a frequency chirp that appears in the temporal interference signal when a large tilting range is scanned. It is shown through a numerical simulation that the chirp depends on the curvature of the illumination wavefront and also on the position of the pivot axis of the illumination beam. Data processing methods are proposed to overcome these limitations and their effects are illustrated with experimental measurements of opaque surfaces and a weakly scattering phantom with internal features. Displacement measurements involving a controlled rigid body rotation and tilt of a weakly scattering phantom were completed to validate the expected deformations. Both in-plane and out-of-plane components were measured

3D space intersection features extraction from Synthetic Aperture Radar images

The main purpose of this Thesis is to develop new theoretical models in order to extend the capabilities of SAR images space intersection techniques to generate three dimensional information. Furthermore, the study aims at acquiring new knowledge on SAR image interpretation through the three dimensional comprehension of the scene. The proposed methodologies allow to extend the known radargrammetric applications to vector data generation, exploiting SAR images acquired with every possible geometries. The considered geometries are points, circles, cylinders and lines. The study assesses the estimation accuracy of the features in terms of absolute and relative position and dimensions, analyzing the nowadays operational SAR sensors with a special focus on the national COSMO-SkyMed system. The proposed approach is original as it does not require the direct matching between homologous points of different images, which is a necessary step for the classical radargrammetric techniques; points belonging to the same feature, circular or linear, recognized in different images, are matched through specific models in order to estimate the dimensions and the location of the feature itself. This approach is robust with respect to the variation of the viewing angle of the input images and allows to better exploit archive data, acquired with diverse viewing geometries. The obtained results confirm the validity of the proposed theoretical approach and enable important applicative developments, especially in the Defence domain: (i) introducing original three dimensional measurement tools to support visual image interpretation; (ii) performing an advanced modelling of building counting only on SAR images; (iii) exploiting SAR images as a source for geospatial information and data; (iv) producing geospatial reference information, such as Ground Control Point, without any need for survey on the ground

Elevation and Deformation Extraction from TomoSAR

3D SAR tomography (TomoSAR) and 4D SAR differential tomography (Diff-TomoSAR) exploit multi-baseline SAR data stacks to provide an essential innovation of SAR Interferometry for many applications, sensing complex scenes with multiple scatterers mapped into the same SAR pixel cell. However, these are still influenced by DEM uncertainty, temporal decorrelation, orbital, tropospheric and ionospheric phase distortion and height blurring. In this thesis, these techniques are explored. As part of this exploration, the systematic procedures for DEM generation, DEM quality assessment, DEM quality improvement and DEM applications are first studied. Besides, this thesis focuses on the whole cycle of systematic methods for 3D & 4D TomoSAR imaging for height and deformation retrieval, from the problem formation phase, through the development of methods to testing on real SAR data. After DEM generation introduction from spaceborne bistatic InSAR (TanDEM-X) and airborne photogrammetry (Bluesky), a new DEM co-registration method with line feature validation (river network line, ridgeline, valley line, crater boundary feature and so on) is developed and demonstrated to assist the study of a wide area DEM data quality. This DEM co-registration method aligns two DEMs irrespective of the linear distortion model, which improves the quality of DEM vertical comparison accuracy significantly and is suitable and helpful for DEM quality assessment. A systematic TomoSAR algorithm and method have been established, tested, analysed and demonstrated for various applications (urban buildings, bridges, dams) to achieve better 3D & 4D tomographic SAR imaging results. These include applying Cosmo-Skymed X band single-polarisation data over the Zipingpu dam, Dujiangyan, Sichuan, China, to map topography; and using ALOS L band data in the San Francisco Bay region to map urban building and bridge. A new ionospheric correction method based on the tile method employing IGS TEC data, a split-spectrum and an ionospheric model via least squares are developed to correct ionospheric distortion to improve the accuracy of 3D & 4D tomographic SAR imaging. Meanwhile, a pixel by pixel orbit baseline estimation method is developed to address the research gaps of baseline estimation for 3D & 4D spaceborne SAR tomography imaging. Moreover, a SAR tomography imaging algorithm and a differential tomography four-dimensional SAR imaging algorithm based on compressive sensing, SAR interferometry phase (InSAR) calibration reference to DEM with DEM error correction, a new phase error calibration and compensation algorithm, based on PS, SVD, PGA, weighted least squares and minimum entropy, are developed to obtain accurate 3D & 4D tomographic SAR imaging results. The new baseline estimation method and consequent TomoSAR processing results showed that an accurate baseline estimation is essential to build up the TomoSAR model. After baseline estimation, phase calibration experiments (via FFT and Capon method) indicate that a phase calibration step is indispensable for TomoSAR imaging, which eventually influences the inversion results. A super-resolution reconstruction CS based study demonstrates X band data with the CS method does not fit for forest reconstruction but works for reconstruction of large civil engineering structures such as dams and urban buildings. Meanwhile, the L band data with FFT, Capon and the CS method are shown to work for the reconstruction of large manmade structures (such as bridges) and urban buildings

Digital Holography and Optical Contouring

Digital holography is a technique for the recording of holograms via CCD/CMOS devices and enables their subsequent numerical reconstruction within computers, thus avoiding the photographic processes that are used in optical holography. This thesis investigates the various techniques which have been developed for digital holography. It develops and successfully demonstrates a number of refinements and additions in order to enhance the performance of the method and extend its applicability. The thesis contributes to both the experimental and numerical analysis aspects of digital holography.Regarding experimental work: the thesis includes a comprehensive review and critique of the experimental arrangements used by other workers and actually implements and investigates a number of these in order to compare performance. Enhancements to these existing methods are proposed, and new methods developed, aimed at addressing some of the perceived short-comings of the method. Regarding the experimental aspects, the thesis specifically develops:• Super-resolution methods, introduced in order to restore the spatial frequencies that are lost or degraded during the hologram recording process, a problem which is caused by the limited resolution of CCD/CMOS devices.• Arrangements for combating problems in digital holography such as: dominance of the zero order term, the twin image problem and excessive speckle noise.• Fibre-based systems linked to tunable lasers, including a comprehensive analysis of the effects of: signal attenuation, noise and laser instability within such systems.• Two-source arrangements for contouring, including investigating the limitations on achievable accuracy with such systems.Regarding the numerical processing, the thesis focuses on three main areas. Firstly, the numerical calculation of the Fresnel-Kirchhoff integral, which is of vital importance in performing the numerical reconstruction of digital holograms. The Fresnel approximation and the convolution approach are the two most common methods used to perform numerical reconstruction. The results produced by these two methods for both simulated holograms and real holograms, created using our experimental systems, are presented and discussed.Secondly, the problems of the zero order term, twin image and speckle noise are tackled from a numerical processing point of view, complementing the experimental attack on these problems. A digital filtering method is proposed for use with reflective macroscopic objects, in order to suppress both the zero-order term and the twin image.Thirdly, for the two-source contouring technique, the following issues have been discussed and thoroughly analysed: the effects of the linear factor, the use of noise reduction filters, different phase unwrapping algorithms, the application of the super-resolution method, and errors in the illumination angle. Practical 3D measurement of a real object, of known geometry, is used as a benchmark for the accuracy improvements achievable via the use of these digital signal processing techniques within the numerical reconstruction stage.The thesis closes by seeking to draw practical conclusions from both the experimental and numerical aspects of the investigation, which it is hoped will be of value to those aiming to use digital holography as a metrology tool