A method for making a time-lapse seismic survey in a marine environment, the
method
designed to eliminate multiple surface reflections and changes in sea state and
conditions. Seismic sources and receivers are positioned at predetermined conditions
for a first set of data in which at least two sets of seismic signals are recorded
at each receiver, proximate in time, such that there are insignificant changes
in the subsurface formation. At a later point in time the seismic source(s) and
receiver(s) are positioned at the same place when the first seismic data set was
generated. A seismic source emits a sound wave and the seismic receiver receives
what will be called a "monitor signal" and the two-way water travel time is again
determined. A model is then developed for the first and second seismic data sets
in that includes the subsurface signal, changes in the subsurface signal and the
effect of multiple reflections. A set of filter functions are then developed to
filter out the multiple reflections based on the two-way water travel times of
the first seismic data set. The first seismic data set, the second seismic data
set and the filter function are then used to calculate the differences in the subsurface
layers over the elapsed period of time between the two seismic data sets.
