Marine EM exploration
AssigneePGS EM Limited
InventorAntoni Marjan Ziolkowski
Life of this patent
Estimating the term…
Abstract
A method for removing the effects of an airwave from marine electromagnetic data comprising providing an electromagnetic source and at least one receiver in the water; measuring the electromagnetic response at a first source-receiver separation; determining a scaled version of the airwave response at a source-receiver separation where the earth response is negligible and using the scaled airwave response to determine the earth response measured at the first separation. Using this method, an improved estimate of the earth's response can be achieved.
Claims17
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.
A system for determining the earth response to an electromagnetic signal comprising:
- an electromagnetic source;
- at least one receiver in water, the at least one receiver being adapted to:
- measure a first electromagnetic response at a first source-receiver separation;
- and
- measure a second electromagnetic response at a second source-receiver separation where the earth response is negligible;
- and
- a processor, the processor being adapted to:
- determine from the second electromagnetic response the airwave response at the second source-receiver separation;
- and
- use the determined airwave response and the measured first electromagnetic response to determine the earth response at the first source-receiver separation by:
- 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 separation 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.
Dependencies are inferred from the claim text.