Mixed pixel analysis and assessment for flood mapping

The most difficult operation in flood inundation mapping using optical flood images is to map the ‘wet’ areas where trees and houses are partly covered by water. This can be referred to as a typical problem of the presence of mixed pixels in the images. A number of automatic information extracting image classification algorithms have been developed over the years for flood mapping using optical remote sensing images, with most labelling a pixel as a particular class. However, they often fail to generate reliable flood inundation mapping because of the presence of mixed pixels in the images. To solve this problem, spectral unmixing methods have been developed. In this thesis, methods for selecting endmembers and the method to model the primary classes for unmixing, the two most important issues in spectral unmixing, are investigated. We conduct comparative studies of three typical spectral unmixing algorithms, Partial Constrained Linear Spectral unmixing, Multiple Endmember Selection Mixture Analysis and spectral unmixing using the Extended Support Vector Machine method. They are analysed and assessed by error analysis in flood mapping using MODIS, Landsat and World View-2 images. The Conventional Root Mean Square Error Assessment is applied to obtain errors for estimated fractions of each primary class. Moreover, a newly developed Fuzzy Error Matrix is used to obtain a clear picture of error distributions at the pixel level. This thesis shows that the Extended Support Vector Machine method is able to provide a more reliable estimation of fractional abundances and allows the use of a complete set of training samples to model a defined pure class. Furthermore, it can be applied to analysis of both pure and mixed pixels to provide integrated hard-soft classification results. Our research also identifies and explores a serious drawback in relation to endmember selections in current spectral unmixing methods which apply fixed sets of endmember classes or pure classes for mixture analysis of every pixel in an entire image. However, as it is not accurate to assume that every pixel in an image must contain all endmember classes, these methods usually cause an over-estimation of the fractional abundances in a particular pixel. In this thesis, a subset of adaptive endmembers in every pixel is derived using the proposed methods to form an endmember index matrix. The experimental results show that using the pixel-dependent endmembers in unmixing significantly improves performance.

Unsteady mixed convection on the stagnation-point flow adjacent to a vertical plate with a magnetic field

An analysis is performed to study the unsteady combined forced and free convection flow (mixed convection flow) of a viscous incompressible electrically conducting fluid in the vicinity of an axisymmetric stagnation point adjacent to a heated vertical surface. The unsteadiness in the flow and temperature fields is due to the free stream velocity, which varies arbitrarily with time. Both constant wall temperature and constant heat flux conditions are considered in this analysis. By using suitable transformations, the Navier-Stokes and energy equations with four independent variables (x, y, z, t) are reduced to a system of partial differential equations with two independent variables (eta, tau). These transformations also uncouple the momentum and energy equations resulting in a primary axisymmetric flow, in an energy equation dependent on the primary flow and in a buoyancy-induced secondary flow dependent on both primary flow and energy. The resulting system of partial differential equations has been solved numerically by using both implicit finite-difference scheme and differential-difference method. An interesting result is that for a decelerating free stream velocity, flow reversal occurs in the primary flow after certain instant of time and the magnetic field delays or prevents the flow reversal. The surface heat transfer and the surface shear stress in the primary flow increase with the magnetic field, but the surface shear stress in the buoyancy-induced secondary flow decreases. Further the heat transfer increases with the Prandtl number, but the surface shear stress in the secondary flow decreases.

Rethinking Media Pluralism : A Critique of Theories and Policy Discourses

This study examines different ways in which the concept of media pluralism has been theorized and used in contemporary media policy debates. Access to a broad range of different political views and cultural expressions is often regarded as a self-evident value in both theoretical and political debates on media and democracy. Opinions on the meaning and nature of media pluralism as a theoretical, political or empirical concept, however, are many, and it can easily be adjusted to different political purposes. The study aims to analyse the ambiguities surrounding the concept of media pluralism in two ways: by deconstructing its normative roots from the perspective of democratic theory, and by examining its different uses, definitions and underlying rationalities in current European media policy debates. The first part of the study examines the values and assumptions behind the notion of media pluralism in the context of different theories of democracy and the public sphere. The second part then analyses and assesses the deployment of the concept in contemporary European policy debates on media ownership and public service media. Finally, the study critically evaluates various attempts to create empirical indicators for measuring media pluralism and discusses their normative implications and underlying rationalities. The analysis of contemporary policy debates indicates that the notion of media pluralism has been too readily reduced to an empty catchphrase or conflated with consumer choice and market competition. In this narrow technocratic logic, pluralism is often unreflectively associated with quantitative data in a way that leaves unexamined key questions about social and political values, democracy, and citizenship. The basic argument advanced in the study is that media pluralism needs to be rescued from its depoliticized uses and re-imagined more broadly as a normative value that refers to the distribution of communicative power in the public sphere. Instead of something that could simply be measured through the number of media outlets available, the study argues that media pluralism should be understood in terms of its ability to challenge inequalities in communicative power and create a more democratic public sphere.