APPLICATION OF SPARSE DICTIONARY LEARNING TO SEISMIC DATA RECONSTRUCTION

According to the principle of compressed sensing (CS), under-sampled seismic data can be interpolated when the data becomes sparse in a transform domain. To sparsify the data, dictionary learning presents a data-driven approach trained to be optimized for each target dataset. This study presents an interpolation method for seismic data in which dictionary learning is employed to improve the sparsity of data representation using improved Kth Singular Value Decomposition (K-SVD). In this way, the transformation will be highly compatible with the input data, and the data in the converted domain will be sparser. In addition, the sampling matrix is produced with the restricted isometry property (RIP). To reduce the sensitivity of the minimizer term to the outliers, we use the smooth L1 minimizer as a regularization term in the regularized orthogonal matching pursuit (ROMP). We apply the proposed method to both synthetic and real seismic data. The results show that it can successfully reconstruct the missing seismic traces

Iterative Separation of Note Events from Single-Channel Polyphonic Recordings

This thesis is concerned with the separation of audio sources from single-channel polyphonic musical recordings using the iterative estimation and separation of note events. Each event is defined as a section of audio containing largely harmonic energy identified as coming from a single sound source. Multiple events can be clustered to form separated sources. This solution is a model-based algorithm that can be applied to a large variety of audio recordings without requiring previous training stages. The proposed system embraces two principal stages. The first one considers the iterative detection and separation of note events from within the input mixture. In every iteration, the pitch trajectory of the predominant note event is automatically selected from an array of fundamental frequency estimates and used to guide the separation of the event's spectral content using two different methods: time-frequency masking and time-domain subtraction. A residual signal is then generated and used as the input mixture for the next iteration. After convergence, the second stage considers the clustering of all detected note events into individual audio sources. Performance evaluation is carried out at three different levels. Firstly, the accuracy of the note-event-based multipitch estimator is compared with that of the baseline algorithm used in every iteration to generate the initial set of pitch estimates. Secondly, the performance of the semi-supervised source separation process is compared with that of another semi-automatic algorithm. Finally, a listening test is conducted to assess the audio quality and naturalness of the separated sources when they are used to create stereo mixes from monaural recordings. Future directions for this research focus on the application of the proposed system to other music-related tasks. Also, a preliminary optimisation-based approach is presented as an alternative method for the separation of overlapping partials, and as a high resolution time-frequency representation for digital signals

The efficient use of data from different sources for production and application of digital elevation models

The emphasis of the investigation reported in this thesis is on the use of digital elevation data of two resolutions originating from two different sources. The high resolution DEM was captured from aerial photographs (first source) at a scale of 1:30,000 and the low resolution DEM was captured from SPOT images (second source). It is well known that the resolution of DEM data depends a great deal on the scale of the images used. The technique for capturing DEMs is static measurement of the spot heights in a regular grid. The grid spacing of the high resolution DEM was 30 m, and of the low resolution DEM was 100 m. The aims of this thesis are as follows: 1. To assess the feasibility of using SPOT stereodata as a source of height information and merged with data from aerial photography. This is carried out by comparison of the elevation data derived from SPOT with the digital elevation data derived from aerial photography. From the comparison of these two sources of height information, some results are derived which show the possible heighting accuracy levels which can realistically be achieved. A systematic error in the estimated average of the elevation differences was found and many tests have been carried out to find the reasons for the presence of this systematic error. 2. To develop methods to manipulate the captured data. 2.1. Gross error (blunder) detection. Blunders made during the data capturing procedure affect the accuracy of the final product. Therefore it is necessary to trap and to remove them. A pointwise local self-checking blunder detection algorithm was developed in order to check the grid elevation data, particularly those which are derived from the second source. 2.2. Data coordinates transformation. The data must be transformed into a common projection in order to be directly comparable. The projection and coordinate systems employed are studied in this project, and the errors caused by the transformations are estimated. 2.3. Data merging. Data of different reliability have to be merged into a single set of data. In this project data from two different sources are merged in order to create a final product of known and uniform accuracy. The effect of the lower resolution source on the high resolution source was studied, in dense and in sparse form. 2.4. Data structure. To structure the data by changing the format in order to be in an acceptable form for DEM creation and display, through the commercially available Laser-Scan package DTMCREATE. 3. DEM production and contouring. To produce DEMs from the initial data and that derived from the two merged sources, and to find the accuracy of the interpolation procedure by comparing the derived interpolated data with the high resolution DEM which has been derived from aerial photography. Finally to interpolate contours directly from the "raw" SPOT data and to compare them with those derived from the aerial photography in order to find out the feasibility and capability of using SPOT data in contouring for topographic maps

A robust surface matching technique for coastal geohazard monitoring

Coastal geohazards, such as landslides, mudflows, and rockfalls, represent a major driver for coastal change in many regions of the world, and often impinge on aspects of the human and natural environment. In such cases, there is a pressing need for the development of more effective monitoring strategies, particularly given the uncertainties associated with the impact of future climate change. Traditional survey approaches tend to suffer from limited spatial resolution, while contemporary techniques are generally unsuitable in isolation, due to the often complex coastal topography. To address these issues, this thesis presents the development and application of a strategy for integrated remote monitoring of coastal geohazards. The monitoring strategy is underpinned by a robust least squares surface matching technique, which has been developed to facilitate change detection through the reliable reconciliation of multi-temporal, multi-sensor datasets in dynamic environments. Specifically, this research has concentrated on integrating the developing techniques of airborne and terrestrial laser-scanning. In addition, archival aerial photography has been incorporated in order to provide a historical context for analysis of geohazard development. Robust surface matching provides a mechanism for reliable registration of DEM surfaces contaminated by regions of difference, which may arise through geohazard activity or vegetation change. The development of this algorithm has been presented, and its potential demonstrated through testing with artificial datasets. The monitoring strategy was applied to the soft-cliff test site of Filey Bay, North Yorkshire. This highlighted the viability of the robust matching algorithm, demonstrating the effectiveness of this technique for absolute orientation of DEMs derived from archival aerial photography. Furthermore, the complementary qualities of airborne and terrestrial laser scanning have been confirmed, particularly in relation to their value for multi-scale terrain monitoring. Issues of transferability were explored through application of the monitoring strategy to the hard rock environment of Whitby East Cliff. Investigations in this challenging environment confirmed the potential of the robust matching algorithm, and highlighted a number of valuable issues in relation to the monitoring techniques. Investigations at both test sites enabled in-depth assessment and quantification of geohazard activity over extended periods of time.EThOS - Electronic Theses Online ServiceEnglish Heritage : British Geological SurveyGBUnited Kingdo