A marine seismic data acquisition system includes a streamer spread including plural streamers; a first set of front sources configured to generate seismic waves; a streamer vessel towing the streamer spread and the first set of the front sources, in front of the streamer spread along an inline direction X; a second set of top sources configured to generate additional seismic waves; and first and second source vessels towing the second set of top sources directly above or below the streamer spread. A number NT of the top sources is larger than a number NF of the front sources.