Marine seismic data acquisition

A method for acquiring marine seismic data, wherein a seismic source arrangement comprises a first seismic source and a second seismic source, the method comprising:

• towing the first seismic source at a first predetermined depth and towing the second seismic source at a second predetermined depth, wherein the second predetermined depth is deeper than the first predetermined depth;
• the first seismic source transmitting pulses, each pulse comprising an upwardly-travelling pressure wavefield, which is reflected at a sea/air interface to become a downwardly-travelling ghost pressure wavefield, and a downwardly-travelling primary pressure wavefield;
• the second seismic source transmitting pulses, each pulse comprising an upwardly-travelling pressure wavefield, which is reflected at the sea/air interface to become a downwardly-travelling ghost pressure wavefield, and a downwardly-travelling primary pressure wavefield,
• wherein the first predetermined depth and a magnitude of the peak pressure of the upwardly-travelling pressure wavefield produced by the first seismic source are selected to create an anelastic region at a sea surface having a reflection coefficient of between −0.45 and 0;
• and
• receiving the pulses transmitted from the seismic source arrangement and extracting data from within a predetermined frequency band of interest.

A method for operating a seismic source arrangement in a marine seismic data acquisition system, wherein the seismic source arrangement comprises a first seismic source and a second seismic source, the method comprising:

• towing the first seismic source at a first predetermined depth and towing the second seismic source at a second predetermined depth, wherein the second predetermined depth is deeper than the first predetermined depth;
• the first seismic source transmitting pulses, each pulse comprising an upwardly-travelling pressure wavefield, which is reflected at a sea/air interface to become a downwardly-travelling ghost pressure wavefield, and a downwardly-travelling primary pressure wavefield;
• the second seismic source transmitting pulses, each pulse comprising an upwardly-travelling pressure wavefield, which is reflected at the sea/air interface to become a downwardly-travelling ghost pressure wavefield, and a downwardly-travelling primary pressure wavefield;
• wherein the first predetermined depth and a magnitude of the peak pressure of the upwardly-travelling pressure wavefield produced by the first seismic source are selected to create an anelastic region at a sea surface having a reflection coefficient of between −0.45 and 0.