Keith Ambrose

DInSAR estimation of land motion using intermittent coherence with application to the South Derbyshire and Leicestershire coalfields

Differential interferometric synthetic aperture radar (DInSAR) is a recognized remote-sensing method for measuring the land motion occurring between two satellite radar acquisitions. Advanced DInSAR techniques such as persistent scatterers and small baseline methods are excellent over urban and rocky environments but generally poor over more rural and natural terrain where the signal can be intermittently good and bad. Here, we describe the Intermittent Small Baseline Subset (ISBAS) method, which appears to improve results over natural, woodland and agricultural terrain. This technique uses a multi-looked, low-resolution approach, which is particularly suitable for deriving the linear components of subsidence for large-scale deformations. Application of the ISBAS method over a coal mining area in the UK indicates that it is able to significantly improve upon a standard small baseline approach.

The lithostratigraphy of the Blue Lias Formation (Late Rhaetian—Early Sinemurian) in the southern part of the English Midlands

Mapping by the British Geological Survey in parts of Warwickshire and Worcestershire has shown the lateral continuity of three distinct lithological units at the base of the Lias Group. These have been named the Wilmcote Limestone, Saltford Shale and Rugby Limestone members of the Blue Lias Formation. The members can be recognized in the type section of the Blue Lias Formation at Saltford, near Bath and as far north as the Leicester area, the northern limit of that formation. Their correlatives can be recognized further north in Nottinghamshire and Lincolnshire, in the South Wales coastal sections and, with less certainty, on the Somerset coast.

Using integrated near-surface geophysical surveys to aid mapping and interpretation of geology in an alluvial landscape within a 3D soil-geology framework

An integrated geological, geophysical and remote sensing survey was undertaken as part of the construction of a high-resolution 3D model of the shallow subsurface geology of part of the Trent Valley in Nottinghamshire, UK. The 3D model was created using the GSI3D software package and the geophysical techniques used included ground-penetrating radar (GPR), electrical resistivity tomography (ERT) and automated resistivity profiling. In addition, the remote sensing techniques of light detection and ranging (LIDAR) and airborne thematic mapping (ATM) were used. The objective of the study was to assess the contribution of these techniques to improve the geological mapping and interpretation of terrace deposits and other geological features. The study site had an area of ~2 km2 and consisted of a Triassic mudstone escarpment, overlain first by a sand and gravel river terrace that extended to the modern floodplain of the River Trent. Automated resistivity profiling mapping proved to be the central tool in identifying and positioning geological features at a greater resolution than would be obtained through traditional geological mapping and borehole observation. These features included i) a buried cliff delineating the south-eastern limits of the incised Trent valley, ii) siltstone beds within the Gunthorpe Member of the Mercia Mudstone Group and iii) the variability of the sediments within the river terrace. A long ERT transect across the site successfully imaged the buried cliff and outcropping siltstone beds on the escarpment. Combined ERT and GPR transects revealed the depth of the sand and gravel deposits (Holme Pierrepont sands and gravels), whilst the GPR provided information about the depositional environment. Remote sensing using light detection and ranging proved essential in the original geological survey because it confirmed the absence of a second river terrace that had been previously thought to exist. This case study demonstrates the importance of combining geophysical techniques with traditional geological survey and borehole analysis, in order to create high-resolution 3D geological models, which are increasingly being used as a platform to understand and solve environmental problems.