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The Tellus airborne geophysical survey of Northern Ireland was conducted over a two year period. Measurements from a fixed-wing aircraft operating at 56 m include magnetic (gradiometer), radiometric and frequency-domain electromagnetic. The survey comprises over 80,000 line-km of coverage and was completed in two phases (2005 and 2006). The large geographical scale and two year duration have combined to raise interesting questions regarding data processing and seasonal adjustments. The radiometric and electromagnetic data sets are completely new for N.Ireland, whereas the magnetic data set is significantly better than the existing one. The preliminary results have excited the interest of the planning, mineral and environmental communities.

New high­resolution airborne geophysical surveys of the UK, undertaken with the system developed under the Joint Airborne­geoscience Capability programme, established between the Geological Survey of Finland and the British Geological Survey, will provide large 4­frequency airborne electromagnetic data sets. These data sets will be used to characterise the conductivity distribution of the subsurface for environmental and exploration purposes. To invert these large data sets in a fast and robust manner we have developed “LC1DINV”, a laterally constrained one­dimensional inversion algorithm. This algorithm inverts simultaneously for all observation points along a profile and regularises the inverse problem by requiring that differences between model parameters at adjacent points be small. We use the conjugate gradient method for minimising the data misfit subject to the lateral constraints and a priori model terms. We have inverted 4­frequency data obtained over Suurpelto, a test area in southern Finland, characterised by conductive clays overlying a highly resistive granitic shield. The results show that LC1DINV can successfully locate the depth extent and variations of the clays. Comparison of these results with those obtained with two other types of inversion shows that LC1DINV produces well­defined layer boundaries and laterally smooth cross­sections.

A number of airborne geophysical surveys have now been conducted in the UK using a fixed- wing system operated jointly by the British and Finnish Geological Surveys. The system provides magnetic, radiometric and frequency domain electromagnetic survey measurements. Regulatory survey permissions force a variety of flight elevations typically between 54 to 244 m. On the fringes of major conurbations, we encounter urban greenspace and brownfield areas. These areas may contain mixtures of infrastructure and built structures together with derelict and green areas. In order to provide valid interpretations of the airborne data, detailed studies of the behaviour of the data to a variety of influences found in the urban fringe of a town have been made. Non-geophysical spatial data sets are increasingly being applied to aid both the processing and interpretation of the survey data. This is particularly true in non-rural areas. Examples from a high-resolution survey acquired across a 5 x 5 km coastal area to the west of Irvine, Scotland are considered.

BGS has recently developed jointly with GTK (Geological Survey of Finland) an advanced airborne geoscience capability and has commenced extended airborne surveying of Northern Ireland with other areas soon to follow. Large multi-frequency electromagnetic data sets comprise an important part of these surveys. In order to aid the interpretation of these data sets, we have developed “LC1DINV”, a laterally constrained one-dimensional inversion algorithm. LC1DINV inverts for the resistivities and thicknesses of a few (two or three) horizontal layers using a regularised conjugate gradient optimisation routine. The inverse problem is stabilised through the use of lateral constraints that ensure that model parameters change smoothly in the horizontal direction while preserving our ability to distinguish layer boundaries. Tests on synthetic models confirm the stability and efficiency of the method.