Acoustic telemetry modems are devices that transmit and receive messages underwater through use of sound waves.

In general, to address important oceanographic questions about coastal ecosystems and make timely and effective use of the knowledge so gained, there is a need for:

multiple moored instruments, distributed across broad regions of the coastal ocean, that sample vertical profiles of water properties-- for example, currents-- throughout the water from surface to bottom, and

a system for real-time delivery of data to shore from such an array of instruments.

As a demonstration of a means by which this second objective can be met, the FRONT project implements an undersea network of acoustic modems that enables wireless subsurface communication among instruments. One benefit is that, with the exception of a minimal number of surface buoys that communicate with shore using the cellular telephone network, each instrument can be housed in a protective trawl-resistant frame on the seafloor so that there is less need to address the difficult engineering issues associated with maintaining components in the water column or at the surface during extended deployments.

The real-time data stream is used for data-assimilative numerical modeling that includes the goal of developing a predictive capability for coastal ocean circulation.

Alternatives to networked acoustic modems involve either laying seafloor cables to each instrument, or providing each instrument with a surface buoy that communicates to and from shore directly. Both these options are costly and impractical given the impetus to focus on the oceanography of coastal areas where there is also heavy commercial shipping and fishing activity. Networked acoustic modems offer advantages of portability, flexibility, and adaptability together with subsurface operations that minimize the exposure of equipment to the problematic sea surface environment.