Beyond underwater acoustic communications

The ability to communicate underwater using acoustic energy in place of electromagnetic energy is rapidly becoming commonplace. Indeed, vendors and academic researchers in many advanced countries are pursuing the development of acoustic modems. The emphasis often varies among these efforts: some, especially academic researchers, focus on increased throughput, or data rate, others investigate the development of undersea networks, and others concentrate on autonomous schemes enabling modems to establish “optimal” links with each other. We focus on low power operations, small size, reliability, and flexibility in application. The Teledyne Benthos approach to modem development is to design for many auxiliary capabilities that, while not explicitly communications functions, rely on the communications capabilities and computing infrastructure of the modem. The internal structure of the Telesonar modem is based on a file-sharing system which supports all aspects of the modem: acoustic and/or sensor (digital) data storage, stored wavefiles (for experimental transmissions), and algorithm implementations. In particular, it supports an SD-card data storage system, currently providing 64 Gbyte of storage. As an example, integration with an ADCP is simply provided by a parallel data storage wherein the ADCP stores data in its native format, and the modem stores exactly the same data, but in a time-stamped file system. This form of storage is known to any remote modem such that any file or files can be uploaded and acoustically transmitted. The remote modem may also query any aspect of the stored data - the amount of storage used, the number of files stored, etc., without impact of any The combination of arbitrary waveform transmission (from stored files) and acoustic data recording was recently used to demonstrate the ability of a specialized waveform for use in highly reverberant and physically constricted environments. This combination of capabilities enabled t- - he complete design, testing, and data analysis to be completed in under one week without the necessity of embedded programming within the modem DSP.