4D FIXED INSTALLATION SEISMIC
Integrated navigation and control system
Paul Newman provides an overview of Gator, the navigation and control software for ocean bottom cable surveys.
Paul Newman gibt einen Überblick über Gator, die Navigations- und Steuersoftware für Kabelvermessungen des Meeresbodens.
Paul Newman ofrece una descripción general de Gator, el software de control y navegación para la exploración del fondo marino a través de cables.
G
ator is a program developed by Concept Systems of Edinburgh – now part of the ION Geophysical
(ION) group, that was designed for the navigation, positioning and operational management of ocean bottom cable (OBC) seismic surveys but is also used for 4D/time lapse surveys and for resistivity surveys using towed electromagnetic transmitters and seabed logging units. Gator interfaces with the acoustic systems used for the positioning of OBC cables, remotely operated vehicles (ROV), seabed logging units and towed equipment. ION is in the process of developing a ‘next generation’ Gator that will utilise elements of its Orca Instrument room command and control software to maximise operational efficiency. Gator runs on computers running
Gator allows centralised managament and operational co-ordination and it helps create a centralised database of all cable positions.
Red Hat Linux and is modular in nature, allowing for efficient updating and program management. Te typical user requires a basic familiarity and working knowledge of Linux, whereas the configuration of a new installation is necessarily more demanding and often requires a Concept Systems engineer to be present. Each Gator computer must be connected
to an ION interface unit (the latest version is known as a Power Real Time Navigation Unit or PRTNU) that houses a GPS card (used for timing), and both serial and Ethernet connections for external devices such as positioning GPS, heading and motion sensors, echo sounders, acoustic positioning systems, radio modems, air- gun triggers and recording systems as well as output to vessel dynamic positioning (DP) systems. Survey planning, software configuration and operational simulations can be performed before the equipment and crews are sent to the field. OBC differs from conventional towed marine seismic acquisition in that the hydrophones and/or accelerometers are placed (in a ‘cable’) on the seabed rather than towed (in a ‘streamer’) at the sea surface. Tis reduces the overall speed of the survey but allows for operations to take place in waters too shallow or otherwise restricted such as close to shore or around offshore platforms, and also has benefits when conducting repeat time-lapse (4D and 4C) surveys as the cables can be left in situ or placed on the same locations. Operations consist of a cable deployment and positioning phase, a shooting/ acquisition phase, and then the recovery and re-deployment of cables to new positions. Tese phases normally involve multiple vessels and crews that are physically separated but that must pass and share timing, navigation and positioning data, and it is this functionality that Gator is able to provide. Te GPS cards in the interface units on each vessel provide high-accuracy timing across the fleet and in particular on for the timing of airgun shot and recording system operation. Te data management and telemetry system allows transfer of vessel and cable positioning data to be transferred in the background and across multiple redundant links to suit the limitations of the survey (frequencies available, the working range of radios etc), with survey specific tailoring of which items are given priority.
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