Abstract: One or more slave acoustic transponders are secured to selected parts of a seismic bottom cable whose location is imperfectly known. A master transponder broadcasts an interrogation pulse from each of a number of different, known locations distributed along a line of survey. In response to an interrogation pulse, a slave transponder emits an encoded signal that is received by the master transponder. The acoustic flight time between each pulse broadcast and encoded-signal reception constitutes a range measurement to the participating slave transponder. Resolving a gather of several range measurement from different known broadcast locations, focussed on an identifiable transponder, defines the transponder location.

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.