Abstract: The application discloses a method of determining the relative positions of a plurality of points located substantially in a common plane at or close to the surface of the sea, which method comprises deploying at each of said points an acoustic element comprising an acoustic transmitter and/or an acoustic receiver; sequentially actuating at predetermined time intervals at least a predetermined number of the acoustic transmitters and observing the responses of at least a predetermined number of the acoustic receivers in response thereto, such that all of the acoustic elements are operated at least once, whether in the transmit or receive mode or in both said modes; and subjecting the observed responses to signal processing to derive the spacing between each receiving element and each transmitting element, and hence to derive the relative positions of said points.

Abstract: A method of marine seismic investigation involves positioning or deploying at a predetermined point close to or within a multi-element seismic source array a calibration source which is an acoustic pressure wave point source which has a far-field seismic signature of broad bandwidth. The radiated pressure wave field of the calibration source (3) is weaker than that of the main source (2). The two sources are fired at separate instants within a predetermined time range, preferably with the calibration source (3) being fired about two seconds before the main source (2). The reflected response of the sub-surface strata is recorded and processed to generate seismic data. In one embodiment, the response is recorded with two hydrophone arrays - a short high-resolution array (4) and a conventional main array (5). The method can be used to determine the far-field signature of the main source array (2). It can also be used to obtain a high-resolution shallow seismic section simultaneously with a deep seismic section.

Abstract: A method of underwater seismic testing is disclosed which does not require the use of long hydrophone streamers and which dispenses with the conventional CDP stack technique. The method enables signal processing to commence as soon as the first shot has been fired. The method involves traversing the region of interest with a survey vessel while firing a single seismic source repeatedly and observing the sub-sea response to the repeated shots using a single seismic receiver to provide thereby single-trace data which is then processed to generate the required sub-sea geological data. The signal processing may be effected in two stages, the first being deconvolution and the second being "3-D" imaging, preferably using the Kirchoff integral formulation.