DIGITAL HOLOGRAPHY APPLIED TO BOREHOLE ELECTROMAGNETIC WAVE EXPLORATION

After a brief description on the prineiples of holography and a discussion on the physical fundamentals relating to the application of holography to borehole electromagnetic wave exploration, the conleept of multiple-hologram and the associated teelmique for its synthetic imaging are presented. It is demonstrated that for bore-hole electromagnetic wave exploration the (curves from various fixed-point and synchronously moving measurements can be processed jointly, using the multiple-hologram synthetic imaging technique, to improve the resolution and image quality. It is also proved that this process of synthetic imaging of the multiple-hologram is equivalent in principle to the imaging process of dual-focussed scanning, in which, both the receiving and the tramsmitting antenna arrays are foeussed sequentially on each imaging point. The two-hole penetration method and the single-hole reflection method have been discussed and the relevant formulas for calculation given. Problems encountered in data processing, such as the interferences caused by source point images as well as their elimination, the problem of screened regions in penetra-tion holography and the problem of double images occurring in samelevel synchronously moving measurements, in which the transmitting and the receiving points are at the same level, are diseussed, supported by the results of computer simulations using the diffraction point model. Finally some results of data processing for water tank experiments and a few tentative calcelations of field data are shown.