The High Resolution Airborne Resource and Environmental Survey- (Phase 1) (HiRES-1): background, data processing and dissemination and future prospects

This report provides an overview of the HiRES-1 airborne geophysical survey of Central England. The BGS and World Geoscience (UK) Ltd. carried out the survey jointly in 1998. The three main survey data sets acquired were magnetic, radiometric (gamma ray spectrometry) and Very Low Frequency (VLF) electromagnetic. The main aim of the report is to provide information on the acquisition, processing and storage of the final data and map products produced by the HiRES-1 project. Additional descriptions of ground truthing activities, data licensing and dissemination are also provided. A significant aspect of the project was the assessment of the potential of, and issues raised by, modern, multi-parameter, regional-scale airborne geophysical surveys in the UK context. Some of the main issues outlined in the report are: • The practical difficulties of conducting extensive low level, fixed-wing geophysical surveying in the UK. Issues discussed include CAA regulatory permissions, flight height adjustments above conurbations and surveying near areas with dense air traffic. • The processing challenges introduced by cultural (nongeological) influences on high resolution airborne magnetic data sets in the UK. • The significant amounts of detailed geological and environmental information contained within the radiometric data. • The weak application potential provided by passive (i.e. VLF) measurements, in contrast to active airborne electromagnetic techniques. The future prospects for regional-scale, airborne geophysical surveys in the UK are considered. Such prospects are also influenced by a further set of trial airborne data, obtained in 1999, but not described here. Further detail of the HiRES-1 survey, productivity, technical specifications and data pre-processing are contained in the survey logistics report prepared by WGL: ‘British Geological Survey “Hi-Res Phase One” Airborne Geophysical Survey (Survey Details, Technical Specifications & Processing Summary)’ (WGL 2000)

Trial airborne environmental and geological survey: an initial appraisal of relevance to land-use

A series of four trial airborne environmental and geological surveys was flown by the Geological Survey of Finland (GTK) in collaboration with the British Geological Survey (BGS) in June 1999; the trials were co-sponsored by the Department of the Environment, Transport and the Regions and the Environment Agency. The main objective of these surveys was to test the efficiency of the GTK airborne electromagnetic system in the mapping of potential pollution problems in the UK environment. Gamma spectrometric and magnetometric measurements were also collected to see to what extent these techniques provide complementary information. This report is an initial consideration of the multi-parameter airborne geophysical data in relation to land-use issues. A variety of earth science information for planning and development already exists. The baseline information is reviewed according to scale and resolution. It is noted that the airborne data is of a new type with regard to both information content and spatial continuity. The specific characteristics and advantages of the airborne geophysical data are emphasised. The trial survey data were obtained at high resolution and a large number of anomalous responses have been observed. Since the information is provided at a local-scale a number of issues concerning the nature of the responses observed and the underlying causes have been raised. It will be necessary to improve our understanding of the data before an unambiguous discussion of their specific relevance to land-use issues can proceed. In advance of detailed interpretations of the trial data, the data are presented and discussed in relation to their potential relevance to five land-use issues: (i) Waste planning/Planning and pollution control, (ii) Minerals Planning, (iii) Water supply and water resource protection/Coastal zone management, (iv) Urban regeneration/Peripheral development and new communities and (v) Agriculture and Forestry. It is acknowledged that there are differences between the information needed for planning the use of land, and information which is required for monitoring environmental strategies. The geophysical data appear to have greatest relevance to the latter requirement. Recommendations for ground and subsurface calibration of the data are made

Trial airborne environmental and geological survey of target areas in the English Midlands

A series of four trial airborne environmental and geological surveys was flown by the Geological Survey of Finland (GTK) in collaboration with the British Geological Survey (BGS) in June 1999; the trials were co-sponsored by the Department of the Environment, Transport and the Regions and the Environment Agency. The main objective of these surveys was to test the efficiency of the GTK airborne electromagnetic (EM) system in the mapping of potential pollution problems in the UK environment. Gamma spectrometric and magnetometric measurements were also collected to see to what extent these techniques provide complementary information. The EM data are particularly encouraging and have identified anomalies which may relate to subsurface pollution. The data have identified conductive zones both on the ‘local’ scale (i.e. possibly emanating from domestic landfills) through to regional scale features up to many kilometres in length. The information obtained in relation to spoil tip drainage is of particular note. The data have provided a wealth of information on ‘point source’ anomalies (requiring ground truth information) and diffuse sources that may be connected with groundwater extraction. At two sites (Trent Valley and Langar) the EM technique appears to have met the challenge of detecting conductive targets in a conductive host. Many other features of the data will take time to assess. The radiometric data indicate features of land fill and colliery spoil sites and allow comparison to be made rapidly with the EM data to define the lateral spread of conductive pore fluids beyond the site itself. They can also be used to map site-specific contamination where radioactive elements are present. The radiometric data also give direct indications of solid and drift geology and soil type, providing additional detail to that shown on geological maps (soil maps are not available for much of the UK). The magnetic data have suggested the presence of significant volumes of metallic debris in the Langar landfill sites. This may be significant in terms of the leachates derived and the compaction (through time) of the contrasting fill materials. Compared with the EM and radiometric techniques, the applications of magnetics in environmental studies are rather limited, but such data is worthwhile collecting in view of the marginal additional costs involved

Applications and challenges for high resolution airborne surveys in populated areas

The role of high resolution airborne surveys is extending well beyond the traditional areas of mineral and hydrocarbons exploration and regional mapping, which were often focused on the relatively unpopulated and remote regions of the world. As an increasing proportion of the Earth’s surface is affected by human activity, airborne survey techniques are being adapted and applied to development-related issues in more populated areas. The value of radiometric and electromagnetic data (in particular) has been recognised for addressing a range of environmental issues and, more generally, airborne surveys are seen as an effective, non-invasive means of providing multiple development-related geoscience data sets in a single operation. These new applications present many operational, processing and interpretation challenges. This paper provides an overview of some of the issues addressed in this Special Session on ‘The role of high resolution airborne surveys in environmental monitoring and sustainable development of resources’

Hydrogeological classification of superficial clays: apparent resistivity measurements from the Garboldisham, Norfolk pilot study area

Three types of apparent resistivity measurements have been undertaken at the Garboldisham pilot study area in Norfolk in support of the superficial clays programme. Resistivity soundings have established the intrinsic resistivities for the strata encountered. Cover sand (possibly mixed with glacial sand) ofresistivities 100 - 200 ohm.m overlies till ofresistivities 22 - 32 ohm.m which lies directly on chalk of resistivities 65 - 85 ohm.m. At the sounding sites, depth to chalk is in the range 11 - 15 m. Azimuthal apparent resistivity measurements were made in an attempt to identify fracture sets within the till and to establish the degree of fracturing between measurement sites. These fracture sets will have an important influence on the hydrogeological regime. At only two of the five sites investigated was a fracture trend recognised and this had an orientation of 210-225 degrees. There was an indication of a change in the intensity of fracturing between the two sites. The results indicate that there is either a lack of fracturing with a consistent trend within the till or that there is an insufficient resistivity contrast between the conductive till and the fractures. Detailed dipole-dipole apparent resistivity measurements undertaken with the BGS RESCAN system were able to map the thickness ofcover sand over a suspected sand channel. The sand body has a north - south orientation with a variable depth to the till surface. Maximum depths are up to two metres. The effectiveness of the resistivity technique for mapping sand lying on till has been demonstrated in this study

Eye in the sky : locating and mapping potential environmental hazards in the UK with high resolution airborne geophysics

During the past fifteen years environmental scientists have applied airborne geophysical techniques increasingly to the mapping and monitoring of potential environmental hazards such as leakages from landfill sites, the spread of polluted groundwaters and the distribution of possibly harmful natural and artificial radionuclides. Explorationists first applied these techniques more than 60 years ago, initially for metallic mineral exploration in Shield areas with subsequent developments in non-geological applications such as the detection of enemy submarines. In later years the techniques have been improved and also applied to hydrocarbon exploration and geological and structural mapping. The rapid emergence of airborne techniques in environmental studies is a response to high profile nuclear accidents, increasingly stringent environmental legislation, the desire of many large corporations for a green image and the numerous benefits delivered by airborne techniques. These latter include relative ease of access to ‘difficult’ sites, comprehensive data coverage and remote, rapid and non-invasive acquisition of data which in turn informs highly focussed confirmatory ground follow up activities. All of these advantages are especially important in potentially hazardous sites. The success of the airborne techniques results from the use of highly sensitive equipment combined with close flight line spacing, generally low ground clearance and accurate navigation and post survey data location based on differential GPS. In this paper we use data from two recent high resolution airborne geophysical surveys in the UK to show how a broad range of environmental management issues can be addressed. In future volumes further contributions will describe the applications of these airborne data sets to resource exploration and geological and structural mapping

Methods for the recognition of geological weakness zones and other surface discontinuities caused by underground mining in Carboniferous terrain

Since March 1992 the British Geological Survey (BGS) has collaborated in a CEC part-funded project under the leadership of Dr Clasen of Saarberg, Saarbrueken, Germany. The aim of this project was to determine the most efficient combination of surface geophysical techniques to be used in combination with airborne optical scanning data for the routine detection of shallow faults. Such features, when reactivated following undermining, may become the locii of damaging subsidence, but where they can be traced in advance of mining operations then remedial measures (such as underpinning etc) may be undertaken. This final report outlines the geophysical methods applied and describes our most significant results. Conclusions are drawn concerning the relative efficiencies of each technique and possible complementary applications

Electrokinetic sounding applied to well and borehole siting : an appraisal

This report is written to summarise the findings of project R6232 whose goal was to improve the assessment, development and management of water resources. The stated purpose was ‘to increase the success rate of well and borehole siting, in diverse hydrogeological environments, by assessing and developing a ‘new’ electrokinetic (EK) geophysical methodology’. With hindsight, the assessment and development requirements have proved to be far more intricate and involved than was originally envisaged. Simple hydrogeological questions (does the method work, or have any value?) have, of necessity, required detailed geophysical research. One of the reasons for the complexity stems from the technical platform used for the assessments. The EK instrument and procedures were purchased from a new company who had developed the world’s first commercial system for EK sounding. The claims made for the system were considerable; the available background to the methodology was minimal. In order to provide objectivity, it has been necessary to review and examine the physical theory alongside the measurement/processing techniques used. These developments had then to be assessed alongside the results of field experiments both in the UK and overseas. A second reason for the complexity has been the nature of the wavefields employed The two fields used are acoustic (source) and electromagnetic (received). Individually both fields are well-defined following established geophysical methodologies which routinely employ them. The EK method exploits subsurface coupling of these wavefields. Theoretical predictions concerning the nature of the fully-coupled wavefields are difficult and limited. To our knowledge there is only one recent paper (Mikhailov et al.,1997) that attempts to deal adequately and practically with the numerical simulation of electrokinetic signals observed in the field. Even this assessment is quite limited