246 ABSTRACTS

channel are recorded on a four-track magnetic tape recorder. The laboratory based

part of the system provides for the play-back and filtering of the records, correc-

tion for tape speed variation and a visual display of the clock time.

INSTRUMENTATION AND DATA PROCESSING OF MARINE

GEOPHYSICAL SURVEYS

A. TURPIE

Bureau oJ’ Mineral Resources, Canberra, A.C.T. (Australia)

(Received September 14, 1970)

A programme of reconnaissance geophysical surveys started by the Bureau

of Mineral Resources in 1965 has made use of recent and developing techniques

in navigation and in gravity, magnetic and seismic measurements. Economic opera-

tion has been achieved by developing a satisfactory 24 hours-a-day navigation

system and geophysical equipment capable of operation at 10 knots. It is emphas-

ized that, in a survey of this nature with a large daily expenditure and limited

budget, once work has started, then in most cases the best results obtainable under

existing conditions must be accepted. Since difficulties and failures must occur,

back-up for as many important systems as possible is required so that failure will

not prevent continuation of worthwhile operations.

The very large quantities of data being acquired make digital processing of

results obligatory. In 1968, a small shipboard digital computer formed part of the

satellite Doppler navigation system, and a digital data acquisition system was used

for the gravity and magnetic and some of the navigation data. In 1970 it is intended

to use two separate small shipboard computers, one for acquisition of the naviga-

tion, gravity and magnetic data and the other for on-line processing of the six-fold

C.D.P. seismic data. Digital processing of the navigation, gravity and magnetic

data is done on a large computer system in Canberra and the results are plotted

and contoured digitally.

Geoexplorution, 8 (1970) 243-251