Patent ID: 8427165

Claim:
A method for determining the earth response to an electromagnetic signal using a source for transmitting the electromagnetic signal to at least one receiver in water, the method comprising: measuring an first electromagnetic response at a first source-receiver seperation; measuring a second electromagnetic response at a larger second source-receiver seperation where the earth response is negligible; determining from the second electromagnetic response the airwave response at the second source-receiver separation; and using the determined airwave response and the measured first electromagnetic response to determine the earth response at the first source-receiver separation, wherein using the determined airwave response and the measured first electromagnetic response to determine the earth response involves: finding an inverse filter f(t) of the determined airwave response â(t); convolving the filter f(t) with the measured response at the first source-receiver seperation to provide a result that includes an airwave impulse; removing the airwave impulse from the result of the convolution; and convolving the remainder with the determined airwave response â(t) to recover the earth response at the first source-receiver separation without the airwave; wherein the earth response comprises a signal with a transmission path directly through the earth.