Two Landsat TM scenes of SW England and a sub-scene of North Cornwall have been
analysed visually in order to examine the effect of resolution on lineament interpretation. Images
were viewed at several different scales as a result of varying image resolution whilst maintaining a
fixed screen pixel size. Lineament analysis at each scale utilised GIS techniques and involved
several stages: initial lineament identification and digitisation; removal of lineaments related to
anthropogenic features to produce cleansed lineament maps; compilation of lineament attributes
using ARC/INFO; cluster analysis for identification of lineament directional families; and line
sampling of lineament maps in order to determine spacing.
SW England lies within the temperate zone of Europe and the extensive agricultural cover
and infrastructure conceal the underlying geology. The consequences of this for lineament
analysis were examined using sub-images of North Cornwall. Here anthropogenic features are
visible at all resolutions between 30m and 120m pixel sizes but lie outside the observation
threshold at 150m. Having confidence that lineaments at this resolution are of non-anthropogenic
origin optimises lineament identification since the image may be viewed in greater detail. On this
basis, lineament analysis of SW England was performed using image resolutions of 150m.
Valuable geological information below the observation threshold in 150m resolution images is
likely, however, to be contained in the lineament maps produced from higher resolution images.
For images analysed at higher resolutions, therefore, knowledge-based rules were established in
order to cleanse the lineament populations.
Compiled lineament maps were 'ground truthed' (primarily involving comparison with
published geological maps but included phases of field mapping) in order to characterise their
geological affinities. The major lineament trends were correlated to lithotectonic boundaries, and
cross-cutting fractures sets. Major lineament trends produced distinct frequency/orientation
maxima. Multiple minor geological structures, however, produced semi-overlapping groups. A
clustering technique was devised to resolve overlapping groups into lineament directional families.
The newly defined lineament directional families were further analysed in two ways:
(i) Analysis of the spatial density of the length and frequency of lineaments indicates that
individual and multiple lineament directional families vary spatially and are compartmentalised into
local tectonic domains, often bounded by major lineaments. Hence, such density maps provide
useful additional information about the structural framework of SW England.
(ii) Lineament spacing and length of the lineament directional families were analysed for
the effect of scale and geological causes on their frequency/size distributions. Spacing of fracture
lineaments were found to be power-law, whereas lengths showed power-law and non-power-law
distributions. Furthermore the type of frequency/size distribution for a lineament directional family
can change with increasing resolution
