Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A seismic survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Some surveys are known as “marine” surveys because they are conducted in marine environments. However, “marine” surveys may be conducted not only in saltwater environments, but also in fresh and brackish waters. One type of marine survey, called a “seabed” survey, involves the deployment of seismic sensors, either cables or nodes on the seafloor. Seabed nodes may include both hydrophones and/or geophones for use in acquiring seismic data. Conventional seabed surveys typically involve the use of a deployment vessel from which seismic sensors are dropped to the seafloor and may be positioned with a remote operating vehicle (ROV). Deployment is especially difficult in deep water where currents can cause units dropped at the sea surface to travel horizontally and away from the desired location. After deployment, the node positions must be accurately determined before a source vessel passes over the seabed sensors. The source vessel then generates seismic waves, which in turn generate data captured by the sensors on the seafloor. Once a particular region is surveyed, the nodes must be retrieved, the recorded data extracted, and redeployed by the deployment vessel. Conventional seabed surveys are thus inefficient due to the time it takes to deploy, position and retrieve the ocean bottom nodes and to download the data captured by the nodes.