Abstract
This thesis describes the development of computer programs for use by the Ancient Monuments Laboratory of the Department of the Environment in the display and interpretation of geophysical data from surveys of archaeological sites. The relative significance of archaeological and other contributions to the instrument response and the characteristics by which archaeological features are recognized in the results are discussed with examples from magnetic and resistivity surveys. Significant anomalies may in part be defined in terms of their lateral extent and so may be emphasised or extracted through two-dimensional spatial filtering techniques as employed in image processing. Filtering procedures have been investigated and applied, and examples of results are described. It is proposed that filtering is usually necessary for resistivity readings which have a wide spatial response, but is of less relevance for magnetic surveys using the fluxgate gradiometer. This detects only at close range so that the output is effectively pre-filtered, and is the standard instrument at the AM Laboratory. The main requirement for processing magnetic results is simply a clear display based on a sufficiently close sample of the signal to allow detailed manual interpretation. Additional numerical operations are required during processing to interpolate to scale and to define the range of display levels, and their effect on image quality is discussed. Two sets of programs have been written, one of which is implemented on a time-sharing system and the other on a minicomputer. Each is interactive so that the treatment may be refined through tests on sections of data, and they have both been used for production processing. Design work now continues with the aim of setting up an extended system with capacity to process very large surveys efficiently. Proposed solutions to problems of program organization, control, and data structure are described.