Summary:
The Acoustic Release Command And Display Equipment (ARCADE) is a system for controlling the operation of underwater acoustic releases. Many commercial acoustic releases are available on the market which (under command from the surface) release ballast weights from a sub-surface mooring to enable recovery. However, each manufacturer requires a unique ship based system (deck unit) to command the acoustic release. Furthermore, confirmation of correct operation is often in the form of a digital display of range from the ship to the sub-surface release which is derived from a single acoustic return from the release. In poor acoustic conditions, these acoustic returns are often not detected by the deck unit and the user can not be certain that the acoustic release has released the ballast. Therefore, ship-time can be lost due to this uncertainty.
The ARCADE system overcomes these problems in two ways:
1) The ARCADE is a software based system, and acoustic commands used to control releases are generated under software control. Potentially, any acoustic release command can be generated for any current or future commercial acoustic release. Therefore, only one deck unit is required for sub-sea moorings using different manufacturers' acoustic releases. Potential uses for such a system are with oceanographic / commercial research vessels which operate more then one type of acoustic release.
2) By commanding the sub-surface acoustic release to generate short acoustic pulses at regular intervals (a ping), the ARCADE increases the signal to noise ratio of the ping by using a standard pulse-to-pulse correlation technique. The acoustic pings are displayed on a waterfall (X axis - range; Y axis - time; Z axis - signal intensity) display which is sweeping across the display at a rate which is synchronized to the sub-surface acoustic ping repetition rate. Therefore, the pinger appears as a straight vertical line on the display when the range from the ship to the sub-surface acoustic release is constant. When the range is reducing the line slants to the left, and when the range is increasing the line slants to the right. Confirmation that ballast has been released under command from the surface and that the mooring is rising to the surface, can be determined visually by the change in slant of the acoustic pinger trace on the ARCADE display. This technique proves useful when operating acoustic releases from ships of opportunity which may be acoustically noisy, and when sea surface conditions generate excessive acoustic noise levels. The ARCADE system was also central in determining the precise location of a lost sub-sea mooring, which was eventually successfully dragged for in 2500m water depth.
The ARCADE has been used at sea and successfully operated commercial acoustic releases deployed at depths of 4800m.