CASE system
The CASE® system is a self-contained, autonomous 4C data acquisition and recording system  developed and patented by SeaBed Geophysical AS. By design, the system offers an unmatched combination of repeatable, high-fidelity 4C data, precise and accurate node positioning, very high system reliability and operational flexibility. The combination of CASE Technology and SeaBed aquistition methodology has proven more efficient than existing cable-based multicomponent data aquistion techniques - especially for large survey geometries and even if only the node-based data can boast a truly wide source-receiver offset distibution for all azimuths.
Since 1997 we have developed and operated autonomous seismic recording equipment for ocean bottom seismic. Based on methodical research, customer-involved engineering and impressive commercial track-record (both in terms of survey size and water depth range) SeaBed is today a world-leader on node-based, multi-component seismic services.
The system family is named CASE (CAble less SEismic system). Each CASE unit consists of one Sensor Node connected to a Control Unit. The Control Unit caters for data recording, telemetry power supply and highly accurate time reference. Because of its modular, self-contained design and its field-proven reliability it offers flexibility in use and a very high system fault tolerance. It is also easy to service and upgrade. The depicted unit has a depth ranting of 600m.
The Sensor Node is equipped with three fixed-axis, mutually orthogonal geophones and a hydrophone. It also contains an inclinometer that allows the sensor tilt to be monitored at a sub-degree precision. The Sensor Node becomes acoustically coupled to the seabed when the lower, tubular section (the "skirt") is planted vertically into the seafloor. The Sensor Node is positioned at a pre-defined distance from the Control Unit and with excellent absolute positioning precision. The standard skirt can be substituded (field-replaceable) by optional designs, if special seabed compositions or sensitive marine biotopes should suggest so.
A hydro-acoustic telemetry system allows data transmission to the surface, primarily for quality control purposes. By way of this acoustic link we are able check crucial parameters like electronics integrity, data recording status, battery status, sensor node tilt etc. These checks are typically carried out on a daily basis during the survey. The acoustic link is also used for control purposes, primarily to start and stop the continuous data recording.
The CASE units can be deployed using different methods. For shallow water use it is common to deploy units one by one, while in deeper water a patented basket deployment solution is used. The latter method allows several units to be simultaneously deployed to the seabed. Deck handling of the Nodes is taken care of by semi-automated handling systems in order to minimize personnel hazard exposure and increase deck handling efficiency.
A seismic field survey involves several hundred CASE units, placed in a regular, sparse grid (typ. 200-500m apart). Thanks to our proprietary sensor design and installation methodology we obtain consistently good, highly repeatable sensor response, regardless of water depth, seabed topography or obstructions on seabed.
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