ABSTRACT
Resistivity measurements have long been used onshore in solving hydrogeological and engineering problems. The difficulties of offshore resistivity measurement are mostly connected to suitable electrode configurations for salt water, electrode materials, and above all a high signal-to-noise ratio. On the other hand, the advantage of utilizing a moving vessel makes it possible to obtain continuous recordings and to build up an integrated multi-sensor system and through a data-logger computer system to provide a continuous processing. In shallow seas with salt and brackish water and soft muddy bottom sediments a three-layer model seems an adequate assumption: a low-resistivity top layer, a low-to medium-resistivity "mud" layer, and a high-resistivity bedrock. The resistivity meter must be able to measure at two separate channels, and the system also needs an echo sounder and a precision navigation system. The geological interpretation of the resistivity measurements is, of course, supported considerably if knowledge from shallow seismic profiles, drillings, grab samples, or similar data are included.
