The roles of temporal and spatial noise in Australian geophysics are outlined. Of the two, temporal noise is more amenable to suppression without increasing the cost of geophysical surveys, whereas the reduction of spatial noise is either labor- or computer-intensive. Up to 1976 the ability to see deep targets in Australia was limited by temporal noise in ground electromagnetics (EM) and radiometrics, and by spatial noise for induced polarization (IP), magnetics, and gravity. Consequently, the greatest opportunities for rapid technological advance existed for the first two techniques.

The exploitation of deep targets was made possible through the development of a new ground EM instrument, SIROTEM. The r.m.s. noise in the field data was decreased tenfold compared to contemporary instruments by more efficient use of the time domain. Surveys across two moderately difficult geophysical targets--the massive sulfide deposits at Elura and Teutonic Bore--yield anomalies that are 38 and 20 times greater than the ambient noise at 10 msec. It is predicted that the Elura deposit would be detectable with the presently marketed SIROTEM if the upper boundary were at a depth of 150 m. A high-current version would detect the Elura target at a depth of 210 m with a 100 by 100 m loop, or at 240 m for a 200 by 200 m loop. Survey costs of A$12.50 per station, or A$500 per sq km for a f rst pass reconnaissance survey are reported.