Chapter 3. Getting started
3.1 Unpacking and packing
The Aquarius OBS is delivered in specially-designed packaging. The packaging should be re-used whenever you need to transport the sensor. Please note any damage to the packaging when you receive the equipment and unpack on a clean surface.
Caution: The Aquarius OBS contains sensitive mechanical components which can be damaged by mishandling. If you are at all unsure about the handling or installation of the device, you should contact Güralp Systems for assistance.
Do not bump or jolt any part of the equipment when handling or unpacking.
Do not kink or walk on the data cable (especially on rough surfaces such as gravel), nor allow it to bear the weight of the sensor.
Do not connect the instrument to power sources except where instructed.
Never ground any of the output signal lines from the sensor.
Warning: The Aquarius OBS with ballast weighs around 350 kg in air and 26 kg in water. Improper storage or handling may cause injury, disability or death. Always follow recognised safety procedures for heavy equipment handling.
3.2 System overview
The heart of the system is the Aquarius Ocean Bottom Seismometer (OBS) unit, which is deployed on the seabed. This is a battery-powered, triaxial seismometer with ancillary multi-parametric sensors and data-logger. The unit may be additionally supplied with an absolute pressure gauge or a hydrophone. The Aquarius is equipped with an acoustic modem to provide data telemetry and status information to the surface and it is designed for deployments on the sea bed of the duration of over a year and with a maximum working depth of 6000 metres. Also included are satellite tracker and LED strobe to aid location during recovery.
During deployment and recovery operations, it is possible to control and configure the Aquarius or offload the data using a PC or the Güralp waterproof deck unit. The Güralp deck unit can also be connected to a surface “dunker” acoustic modem providing data telemetry from the deployed Aquarius in the water. Being equipped with lithium ion batteries, the Güralp deck unit can be operated on deck without the use of any mains electricity supply.
The Aquarius battery can be re-charged using the charger unit provided with the system.
3.2.1 The Aquarius
The Aquarius is the sea-floor unit of the system. It includes a weak motion triaxial digital broadband velocity seismometer, which is operational at any angle, without the need of any gimbals system. A three-axis magnetometer and a MEMS accelerometer allow calculation of the main sensor’s 3D position on the seabed.
Additional sensors included are: a Keller piezoresistive pressure transducer, used to measure the depth of the OBS and to automatically turn on the recovery aids when the system is rising back to the surface. Optionally the Aquarius may also include a Paroscientific Absolute Pressure Gauge (APG) used to measure accurate water column pressure variations or an ultra-low frequency pressure compensated hydrophone.
All the sensors transmit data to an Ultra Low Power Digitiser (ULPD), which monitors and controls the system. The ULPD is always running when power is provided. Seismic and environmental data is temporally stored in the volatile memory (RAM) of the ULPD and flushed into the dual redundant Micro SD cards of a Low-Power Computer (LPC) every 45 minutes.
The LPC is mainly powered off and it can be waken up using the power switch activated by the ULPD when a data flush is needed or in case of activity of the integrated acoustic modem, for more details see Section 4.
The acoustic modem with directional or omni-directional transducer is installed to communicate with the deck unit during deployment and recovery. Most of the time the acoustic modem is in sleep mode and it wakes up when it receives an acoustic wakeup signal or when receiving data from the LPC serial.
The OBS is powered by rechargeable Lithium-ion batteries sized to last for up to fifteen months of deployment.
The Burn-Wire release system can be activated either by the acoustic modem when receiving the related release command, or by a timer in the ULPD.
The ULPD also controls the satellite tracking system and the LED strobe, which are activated during the recovery procedure.