Over the past three years the Geophysics Division and co-workers have developed an ultra light airborne mapping facility. It consists of a Streak Shadow ultralight aircraft which records the following data sets namely a) total field magnetic, b) 512 channel gamma-ray spectrometric, c) pulsed, wide-band time domain electromagnetic, and d) 512 channel near infra-red reflected light. The purpose of this facility is to geophysically map areas identified for exploration, mapping or environmental monitoring, in unprecedented detail, much more cost effectively than ground surveys or helicopter borne surveys. Routine survey specifications for the Streak Shadow are 50m flight line spacing, flying 50m above surface (terrain and weather conditions permitting).

Throughout the world, airborne geophysical surveys are used in exploration and regional mapping, In these applications, the ability to rapidly cover large areas of ground at reasonably good sampling intervals, make helicopter or aeroplane borne instruments extremely efficient and cost effective. Ground-based methods remain however the mainstay of environmental and engineering geophysics, where small high resolution surveys are the order of the day. Particularly in these fields and in small and medium scale groundwater exploration, we have identified a space, where larger survey size (up to about 1000 line kilometres) makes ground surveying extremely costly and time consuming while the mobilisation costs make airborne surveying prohibitively expensive. Furthermore, some areas have difficult access, owing to lack of infrastructure , rugged terrain and obstacles, such as landmines in .several African countries. For these reasons, the Council for Geoscience in South Africa set about developing an intermediate geophysical platform, to bridge the gap between ground and conventional airborne surveys.

From the need to perform geophysical surveys cheaper and faster the GeophysicsDivision started experimenting with a remotely piloted drone with a magnetometerand GPS. Since this technology is still relatively underdeveloped the experimentsbranched out to using a Streak Shadow microlight plane with modernexperimental fluxgate magnetometer and lightweight 512-channel gamma-rayspectrometer coupled to a real-time GPS system. Ultra high-density surveys cantherefore be flown at greatly reduced cost. An airborne TDEM system is currentlyalso being developed.

Magnetotelluric sounding stations were placed on a 20 krn interval on the Sishen-Keimoes seismic line. The data were sampled and processed using software developed by the Geological Survey. A new processing technique, namely robust M-estimation, was used in the estimation of the irnpedance function. The data were modeled one dimensionally and two dimensionally.

Magnetotellurics is a frequency domain technique where the earth’s natural electromagnetic field is used as a source. The solar wind (charged particles emitted by the sun) interact with the earth’s magnetic field by ‘pushing’ it to and through, which induces currents in the earth’s crust according to Maxwell’s first law.

Recent advances in radar instrumentation offer high resolution subsurface profiling of features at distances of several metres to several tens of metres in low attenuation material such as sand, gravel, rock and fresh water. The distance may decrease to a few metres in high attenuation material such as day and saline water. With detection distances like these, radar promises to become an important tool for geotechnical, environmental and archaeological investigations.