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Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team. There are several distinct forms of diver communications: *Voice communications – Most professional surface supplied diving equipment uses full face diving masks and diving helmets which include voice communication equipment. *Video communications – Surface supplied divers often carry a closed circuit video camera on the helmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can be used to transfer signals to the surface if voice comms fails, and is in itself a one way mode of communicating useful data to the surface. *Text communications – Underwater slates may be used to write text messages which can be shown to other divers,〔Agnew, J. (2003): Scuba Diver's Travel Companion, The Globe Pequot Press, Guilford, CT, ISBN 0-7627-2668-7〕 and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through water to other divers or surface personnel with compatible equipment.〔("UDI Dive Computer Can Send Underwater Text Messages" ). Retrieved 2013-08-27〕 *Non-verbal communications: * *Hand signals – Recreational divers do not usually have access to voice communication equipment, and it does not generally work with a standard scuba demand valve, so they use other signals. Hand signals are generally used when visibility allows, and there are a range of commonly used signals, with some variations. These signals are often also used as an alternative by professional divers * *Line signals (rope pulls) – Rope signals can be used if the diver is connected to another diver or tender by a rope or umbilical. There are a few partly standardised codes using "pulls" and "bells" (a pair of short tugs). These are mostly used as backup signals by professional divers in the event that voice communications fails, but can be useful to recreational and particularly technical divers, who can use them on their surface marker buoy lines to signal to the surface support crew. * *Light signals – Made using an underwater torch at night. There are not many standard light signals. Suitably skilled divers can transmit morse code using a light. * *Cave line symbols – these are symbols attached to cave lines, indicating critical information such as the direction to the exit. * *Sign language Divers who are familiar with a sign language such as American sign language and equivalents may find it useful underwater, but there are limitations due to the difficulty of performing some of the gestures intelligibly underwater with gloved hands and often while trying to hold something. * *Tap codes – made by knocking on the walls, are used occasionally to communicate with divers trapped in a sealed bell or the occupants of a submersible during a rescue. * *Rattle – a tube containing ball bearings used by guides of large groups to attract attention. * *Miscellaneous emergency signals – Including the use of mirrors, compressed air sirens, whistles, noisemakers, colour-coded Delayed Surface Marker Buoys etc., to alert the surface support personnel of a problem * *Diver down signals – The dive flags, lights and shape signals used to indicate the presence of divers in the water. ==Voice communications== Both hard-wired (cable) and through-water electronic voice communications systems may be used with surface supplied diving. Wired systems are more popular as there is a physical connection to the diver for gas supply in any case, and adding a cable does not make the system any different to handle. Wired communications systems are still more reliable and simpler to maintain than through-water systems. The communications equipment is relatively straightforward and may be of the two-wire or four-wire type. Two wire systems use the same wires for surface to diver and diver to surface messages, whereas four wire systems allow the diver's messages and the surface operator's messages to use separate wire pairs. A standard arrangement with wired diver communications is to have the diver's side normally on, so that the surface team can hear anything from the diver at all times except when the surface is sending a message. This is considered an important safety feature, as the surface team can monitor the diver's breathing sounds, which can give early warning of problems developing, and confirms that the diver is alive. Divers breathing helium may need a decoder system which reduces the frequency of the sound to make it more intelligible. Through water communications systems are more suitable for scuba as the diver is not encumbered by a communications cable, but they can be fitted to surface supplied equipment if desired. Most through water systems have a Push To Talk (PTT) system, so that high power is only used to transmit the signal when the diver has something to say. For commercial diving applications this is a disadvantage, in that the supervisor can not monitor the condition of the divers by hearing them breathe. Dry bells may have a through water communication system fitted as a backup.〔''The Diving Supervisor’s Manual'', First edition, 2000. The International Marine Contractors Association, London. www.imca-int.com ISBN 1-903513-00-6〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diver communications」の詳細全文を読む スポンサード リンク
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