Abstract: An underwater acoustic receiver apparatus (100) comprises an acoustic reflector (102, 104, 106, 108) and an acoustic device (110, 114, 116, 118) aimed at the acoustic reflector (102, 104, 106, 108). The acoustic reflector (102, 104, 106, 108) is disposed at a predetermined distance and orientation relative to the acoustic device (110, 114, 116, 118).

Abstract: An in-situ pressure sensor bias determination apparatus (300) comprises a measurement pressure sensor (400), a reference pressure sensor (402), an electronically controllable pressure adjustment device (406), and a fluid conduit network (410) having an ambient access port (412). The measurement pressure sensor (400) has a greater operating pressure range than the reference pressure sensor (402). The measurement pressure sensor (400), the reference pressure sensor (402) and the pressure adjustment device (406) are sealingly coupled to the fluid conduit network (410) so as to define a volume that is open only at the ambient access port (412). An ambient isolation device (420) is arranged to isolate selectively the ambient access port (412) from the measurement pressure sensor (400), the reference pressure sensor (402) and the pressure adjustment device (406), thereby closing the open volume.

Abstract: An in-situ pressure sensor bias determination apparatus (300) comprises a measurement pressure sensor (400), a reference pressure sensor (402), an electronically controllable pressure adjustment device (406), and a fluid conduit network (410) having an ambient access port (412). The measurement pressure sensor (400) has a greater operating pressure range than the reference pressure sensor (402). The measurement pressure sensor (400), the reference pressure sensor (402) and the pressure adjustment device (406) are sealingly coupled to the fluid conduit network (410) so as to define a volume that is open only at the ambient access port (412). An ambient isolation device (420) is arranged to isolate selectively the ambient access port (412) from the measurement pressure sensor (400), the reference pressure sensor (402) and the pressure adjustment device (406), thereby closing the open volume.

Abstract: An offshore GNSS reference station apparatus comprises: a processing resource and an underwater acoustic communications unit. The underwater acoustic communications unit comprises an underwater acoustic transducer, the underwater acoustic communications unit being arranged to cooperate with the processing resource in order to calculate a position. The apparatus also comprises a GNSS antenna site and an orientation determination unit operably coupled to the processing resource. The orientation determination unit is arranged to determine an orientation associated with the GNSS antenna site and the acoustic transducer of the underwater acoustic communications unit.

Abstract: A subsea measurement system (400) comprises a first reference beacon (110) disposed at a first known location, a second reference beacon (112) disposed at a second known location, and an acoustic communications module (302) for coupling to a subsea element to be monitored. The acoustic communications module (302) is capable of moving, when in use, relative to the first reference beacon (110) and the second reference beacon (112). The acoustic communications module (302) also comprises a processing resource and is arranged to determine first range-related data to the first reference beacon (110) in response to receipt of a first signal by the acoustic communications module (302) from the first reference beacon (110) and second range-related data to the second reference beacon (112) in response to receipt by the acoustic communication module (302) of a second signal from the second reference beacon (112).

Abstract: A data collection system 100 for estimating a corrected sound speed between a first point and a second point comprises a subsea acoustic transponder beacon (106) disposed at a fixed position relative to a seabed (108), and an acoustic transceiver (214) immersed below a sea surface (104) and above the acoustic beacon (106). A processing resource (200) is also operably coupled to the acoustic transponder (214), the acoustic transceiver (214) being arranged to traverse a path above the acoustic beacon (106) and communicate with the acoustic beacon (106). The processing resource (200) is also arranged to collect time-of-flight data associated with the communication between the acoustic transceiver (214) and the acoustic beacon (106).

Abstract: An aquatic time synchronisation system includes an aquatic first acoustic communications apparatus capable of communicating acoustically with a dynamic aquatic second acoustic communications apparatus. The first acoustic communications apparatus includes a first time source and the second acoustic communications apparatus includes a second time source. The first acoustic communications apparatus is arranged to communicate a first acoustic signal to the second acoustic communications apparatus and the second acoustic communications apparatus is arranged to communicate a second acoustic signal to the first acoustic communications apparatus in reply to the first acoustic signal. The first acoustic communications apparatus is arranged to use data associated with the first and second acoustic signals in order to determine a time offset between the first and second time sources.

Abstract: A system and method measures the time offsets of a plurality of acoustic sensor nodes relative to a reference time. The system includes an acoustic transceiver arranged to transmit a first signal to each acoustic sensor node and a processing resource arranged to record the transmission time of the first signal relative to the reference time. The acoustic sensor nodes receive the first signal and transmit a return second signal to the acoustic transceiver after a predetermined time delay, the second signal including the current acoustic sensor node internal time. The acoustic transceiver receives the second signal, and the processing resource records the time at which the second signal was received relative to the reference time and records also the combined time of flight of the first and second signal. From this data the time offset between the sensor node internal time and the reference time is calculated.

Abstract: A system and method measures the time offsets of a plurality of acoustic sensor nodes relative to a reference time. The system includes an acoustic transceiver arranged to transmit a first signal to each acoustic sensor node and a processing resource arranged to record the transmission time of the first signal relative to the reference time. The acoustic sensor nodes receive the first signal and transmit a return second signal to the acoustic transceiver after a predetermined time delay, the second signal including the current acoustic sensor node internal time. The acoustic transceiver receives the second signal, and the processing resource records the time at which the second signal was received relative to the reference time and records also the combined time of flight of the first and second signal. From this data the time offset between the sensor node internal time and the reference time is calculated.