168 (‘OMI’UTER APPLICATIONS

A COMPARISON OF DIGITAL FILTERING AND POWER SPECTRAL ANALYSIS TECHNIQUES IN THE ANALYSIS OF MAGNETO-TELLURIC DATA

H. TAMMEMAGI

Australian National lJniversit_y, Canberra, A.C. T. (Australia)

(Received February 9, 197 1)

Magneto-telluric data from the fake Superior region of Canada was analyzed using the standard power spectral technique as well as a digital filtering method. The high resistivity values as well as the large anisotropies of the resulting apparent resistivity versus period curves were substantiated by both methods. However, the filtering method indicated that the magnetic and orthogonal electric field components were more coherent than the same spectral parameter indicated

THE GEODETIC SURVEY OF AUSTRALIA: AN AID TO GEOPHYSICAL RESEARCH AND DATA RETRIEVAL

K. LEPPER’I

Division of National Mapping, Canberra, A.C. T. (Australia)

(Received February 9, 1971)

In 1966, all the geodetic surveys in Australia and New Guinea, some 33,100 miles of geodetic traverse linking 2506 stations, were adjusted on a single homogeneous system, the Australian Geodetic Datum (AGD), on which all new mapping is now produced. New points are continually being added, and there are now over 5700 points on the AGD. The Australian Map Grid (AMG) provides rectangular coordinates, eastings and northings in metres, in 6” zones, by a transverse mercator projection of coordinates on the AGD. The AGD and AMG provide Australia with a uniform point reference system which is suitable for automatic data retrieval. A Technical Manual on the AMG will be published in 1970 by the Division of National Mapping, who can often assist other organisations with the transformation of existing surveys to the AGD. Coordinates on the AGD will be linked into the Pageos World Satellite Triangulation in 197 1. There are three Pageos camera stations in Australia, and others at Cocos Island, Heard Island, Mawson and Casey. Eight doppler satellite tracking stations have been coordinated on the AGD.

At the end of 1970, about 100,000 miles of levelling, with permanent marks at inter- vals of 1 to 5 miles, will be adjusted to form a homogeneous system called the Australia Height Datum (AHD), covering the whole of Australia, to which all other heights will be referred. The AHD will be tied into 32 tide gauges around the Australian coast.

There are now 9,000 miles of astro-geodetic geoid profile in Australia, and a new map of the geoid will be published in 1970.