A system for surveying the structure beneath the seabed, comprising: a survey vessel; a controller on-board the survey vessel; a sound source; a streamer comprising a cable, a first set of N1 sensor groups positioned at a first end portion of the cable, the sensor groups of the first set being spaced from each other by a group interval, and a second set of N2 sensor groups positioned at a second end portion of the cable, the sensor groups of the second set being spaced from each other by the group interval; wherein the streamer and the sound source are configured such that, when towed, the first end portion of the cable is the leading end portion of the cable and the sound source is positioned adjacent an intermediate portion of the cable between the first and second end portions of the cable, wherein, for both sets of sensor groups, each sensor group is numbered consecutively with the sensor group closest to the sound source being numbered 1; wherein, the system is adapted such that, in use, the survey vessel tows the streamer and the sound source at a predetermined speed; the controller controls the sound source such that the sound source sends acoustic pulses at a predetermined period between pulses towards the seabed, each pulse being shaped such that reflections are produced towards both the first set of sensor groups and the second set of sensor groups; characterized in that the system is adapted such that the speed of the survey vessel and the period between pulses of the sound source are selected such that the shot point interval of the sound source equals the group interval; wherein the controller receives reflection data from the sensor groups, wherein, for a given common mid point, the reflection data consists of either (i) reflection data gathered from the oddly numbered ones of the first set of sensor groups and reflection data gathered from the evenly numbered ones of the second set of sensor groups or (ii) reflection data gathered from evenly numbered ones of the first set of sensor groups and reflection data gathered from oddly numbered ones of the second set of sensor groups, and the reflection data corresponds to all possible offsets. a survey vessel; a controller on-board the survey vessel; a sound source; a streamer comprising a cable, a first set of N1 sensor groups positioned at a first end portion of the cable, the sensor groups of the first set being spaced from each other by a group interval, and a second set of N2 sensor groups positioned at a second end portion of the cable, the sensor groups of the second set being spaced from each other by the group interval; wherein the streamer and the sound source are configured such that, when towed, the first end portion of the cable is the leading end portion of the cable and the sound source is positioned adjacent an intermediate portion of the cable between the first and second end portions of the cable, wherein, for both sets of sensor groups, each sensor group is numbered consecutively with the sensor group closest to the sound source being numbered 1; wherein, the system is adapted such that, in use, the survey vessel tows the streamer and the sound source at a predetermined speed; the controller controls the sound source such that the sound source sends acoustic pulses at a predetermined period between pulses towards the seabed, each pulse being shaped such that reflections are produced towards both the first set of sensor groups and the second set of sensor groups; characterized in that the system is adapted such that the speed of the survey vessel and the period between pulses of the sound source are selected such that the shot point interval of the sound source equals the group interval; wherein the controller receives reflection data from the sensor groups, wherein, for a given common mid point, the reflection data consists of either (i) reflection data gathered from the oddly numbered ones of the first set of sensor groups and reflection data gathered from the evenly numbered ones of the second set of sensor groups or (ii) reflection data gathered from evenly numbered ones of the first set of sensor groups and reflection data gathered from oddly numbered ones of the second set of sensor groups, and the reflection data corresponds to all possible offsets.