A Novel Method for Travel-Time Measurement for Geophysical Inversion Problems

We present a novel method for travel-time measurement for geophysical inversion problems. Instead of computing travel-times through measurement of the propagation delay of a "one-shot" disturbance sent between a source-receiver pair (the "conventional" approach), in our system we establish a continuous spread-spectrum acoustical communications link between the source and the receiver. Then, we send over this link time-stamped data that, when recovered at the receiver, facilitates travel-time measurement. The principal novelty of our approach is that the problem of eliminating the effects of unwanted wave reflections and refractions which arrive at the receiver is transformed into the problem of reducing multipath interference in a spread-spectrum communications system, a topic which has been the subject of extensive research over recent years and for which many proven techniques are available. In this paper we present the theory behind our approach, as well as simulation results obtained through use of a simulation program developed by the authors.