<title>Slimline borehole radar for in-mine use</title>

Abstract

Borehole radar has shown its value in delineating geological features, especially orebody geometry, in deep level gold and platinum mines in South Africa. At the same time, the cost of the critical components of a radar system has decreased dramatically while their performance has increased. The time is ripe for the introduction of a 100 MHz bandwidth instantaneous sampling slimline borehole radar to fit into 38 mm boreholes. A new generation of low cost, low current, fast analogue to digital converters (ADCS) has made it possible to implement instantaneous sampling in the probe. Memory speed is still limited, with speeds beyond 100 MHz not readily available. The borehole radar design uses four 8 bit 100 MS/s analogue to digital converters (ADC5) in parallel, each feeding its own First-In First-Out (FIFO) memory. The four ADC5 are each clocked 2.5 ns apart, to achieve a sampling rate of 400 MS/s. Once the trace has been acquired, it is downloaded from the FIFOs to the onboard microprocessor, where it is stacked. The resultant trace is transmitted out of the borehole using a 1 1 5 kbaud serial link over an optical fibre cable and displayed in real time on the surface control unit Data is processed using conventional GPR processing techniques. Once the data has been filtered, it is transferred to a 3D visualization environment, where reflectors can be compared to inferred target horizons. More complex environments can only be interpreted by using data from multiple boreholes, or by using directional antennas.