Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1 – 24 kHz) to produce decimetre vertical resolution crosssections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. The design incorporates 4 source transducers (1.5 – 13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a preamplifier.It was concluded that the only way to determine with sufficient accuracy the source-receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude
system incorporating four antennas to give position, heading, pitch and roll. The complete system is described and initial navigational and seismic data results are presented for a 3D
seismic volume over folded geological events within the West Solent (UK). These data demonstrate that the approach of using a fixed source-receiver geometry combined with RTK navigation will provide complete 3D imaging of the sub-surface
