Method and apparatus for marine electrical exploration

A method of measuring and analyzing measurement data from an electromagnetic survey of a geological target area that potentially contains a hydrocarbon reservoir,

• the method comprising the step of
• A) measuring a measurement vector u between receiver electrodes, said measurement vector u comprising a plurality of measurement signals ui, wherein
• at least one of the plurality of measurement signals ui is dependent on a geological characteristic mk at a geological parameter index k, where said geological characteristic mk provides information about the geological structure of the geological target area,
• wherein the method further comprises the following step:
• B) calculating a transformed vector v as a function of the measurement vector u. where each component v(k,t) of the transformed vector v at a geological parameter with index k and a time t is calculated by projecting the measurement vector u in the direction given by a unit vector e(k,t), said unit vector e(k,t) being governed by the geological characteristic mk,
• said transformed vector v being designed to optimize the sensitivity to changes in the geological characteristic mk by performing, for each time t, at least one of
• minimizing uncertainty δv(k,t) of the transformed vector v with respect to the geological characteristic mk,
• where said uncertainty δv(k,t) comprises a non-systematic uncertainty δv′(k,t) and a systematic uncertainty Δwdv(k,t),
• maximizing a target response ∂v(k,t)/∂mk of the transformed vector v with respect to the geological characteristic mk and
• minimizing a ratio ψ(k,t) between at least the square of the non-systematic uncertainty <δv′(k,t)2> of the transformed vector v and the square of the target response (∂v(k,t)/∂mk)2 of the transformed vector v with respect to the geological characteristic mk.