Divers Acoustic Communications

ABSTRACT A brief history of divers acoustic communications is given, the needs are defined, several technical approaches are described, and development past, present, and future are discussed. The paper is devoted to divers acoustic communications equipment used by the working diver in operational situations where high intelligibility and "hands free" operation are required. The equipment will be used by the salvage diver, ship husbandry diver, or any other working diver requiring communication. The results of recent development are described, including a patented voice-operated, noise-immune, transmit switch (VOX). The meaning and methods for measuring intelligibility are described. Plans for development effort and schedules to provide the working diver with standard, logistically supportable, underwater acoustic diver communication equipment are discussed. INTRODUCTION The hard-hat diver has had limited communications since 1925, but the free diver has been without reliable communication for four decades. While diving equipment, particularly self contained, is becoming more sophisticated and reliable, communications equipment is not keeping pace with other developments. We can talk to an astronaut on the moon, but we cannot communicate satisfactorily with an untethered diver a few feet from a pier in shallow water. Navy and civilian acoustic communications requirements cover a broad spectrum of needs and environments. They range from the ship husbandry diver working underneath a ship in harbor to underwater construction operation in the arctic, combat swimmer operations, and offshore oil rigs. Early efforts to find workable underwater communications involved the use of surface communication equipment adapted to underwater use. These early attempts were doomed to failure by this approach and the limitation imposed by early technology. Underwater communications require equipment designed for that purpose and treated as a complete system, not a group of individual components. Early designs were misled by the apparent attractive features of various modes of transmission through water such as magnetic field, electric field, and even radio and direct voice insertion. The magnetic field mode is extremely limited in range partly due to the limited power supply the diver can carry even though ambient acoustic noise is eliminated. The electric field mode has many limitations imposed be the laws of physics in addition to the amount of electric current density the diver can withstand. Radio frequencies are attenuated rapidly in water, making adequate range an impossibility with the power supply available to the diver. Direct voice insertion is the use of an underwater loudspeaker (swimming pool speaker). This mode suffers from a lack of range, distortion as a function of range, and in military applications, mission compromise. While other names have been given to some of the above techniques, under close analysis they all fall into one of the above categories. ESSENTIAL CHARACTERISTICS OF DIVER COMMUNICATIONS Three-distinct types of communications systems are required by the diver (Fig. 1):hard wire for the tethered diver,helium speech communications for deep diving applications, tethered and untethered, andthrough the water (wireless) communication.