Publications

The high sensitivity aeromagnetometric method (HSS) was perfected during a large scientific survey called “Magnetic Map of France", flown in 1964 - 1965. This means that the equipment and the technical tolerances of the measurements were improved over a distance of approximately 60,000 miles, under the control of specialists from the “Institut de Physique du Globe" of Paris, operating under the name of "Centre National de la Recherche Scientifique". In such conditions the new airmag method received its best "baptism certificate". Many papers have been published from that date up to the present, a complete list of which is given in the biography index. Among these, we think the following are most relevant to our present subject:- “A new airborne magnetometer: the cesium vapor magnetometer" by R. Giret and L. Nalnar - Geophysical Prospecting, Volume XIII, 2, 1965, “La nouvelle carte magnetique de France" by E. Le Borgne and J. Le Mouel, Note IPG, Paris, no 15, May 1966, "Recent developments in the acquisition, processing and interpretation of high sensitivity aeromagnetic data" by G. Royer, J. Thomas, H. Naudy and H. Dreyer, CGG paper, "Example of digitised navigation airmag surveys on off-shore areas " by G. Royer, Offshore Technology Conference paper in OTC 1306. There is no point in repeating the contents of these papers in detail. However, we can draw the following conclusions, because they are still evident in our surveying operations, especially in Indonesia:- Accurate navigation, flexibility of the measurement grid regarding the geological problem and the accuracy of the measurement, importance of the ground station, necessity of correcting the change in magnetometer altitude. From 1965 the interpretation of measurements was considerably improved in the following ways: complete collection of abacus (see ITX gamma method), special processing: non-linear filtering, upward continuation of the total magnetic field, vertical gradient, automatic calculation of depth estimates, cross correlation, two-dimensional models. Obviously, we are assuming that all data are processed in a computer center from completely digitised field data. In particular, the isogam maps and their transformed maps are obtained by a series of computing programmes.