Patent ID: 7925443

Claim:
A method for conducting a controlled-source electromagnetic survey of the subsurface of a survey area, comprising: (a) dividing the survey area into at least two parts; (b) selecting a part of the survey area; (c) deploying electromagnetic receivers in a predetermined array on a grid in the selected part of the survey area; (d) moving an electromagnetic source to a plurality of positions along predetermined source lines on said grid, and recovering recorded electromagnetic data from the receivers; and (e) sending the data to be analyzed while, concurrent with the analysis, repeating steps (b)-(d) for a next part of the survey area; wherein upon finding that the analyzed data from said selected part of the survey area reveal a resistive anomaly satisfying a predetermined criterion, a vicinity around said resistive anomaly is resurveyed using a more narrow band source waveform than was used before, said narrow band source waveform chosen to focus electromagnetic energy at the depth of the resistive anomaly, said resurvey being conducted before moving survey equipment substantially farther away from said anomaly.