Acoustic Communication 15.3 Existing Technology 361
Part B | 15.3
turbances, as well as the detection of objects on the
ocean floor, and transmission of images from remote
sites. Implicitly, wireless signal transmission is also
crucial for monitoring and control of remote instruments, and for communicating with robots and AUVs,
which can serve on isolated missions, or as parts of
a mobile network. Applications involving AUVs range
from search and survey missions to supervisory control
and collection of mapping data, be they images, video,
or side-scan sonar.
Autonomous systems are envisioned both for standalone applications and as wireless extensions to cabled
systems. For example, a stand-alone 15 kbps acoustic
link, intended to provide data transfer from bottommounted, battery-powered instruments such as seismometers to a surface buoy is described in [15.5].
A different example is that of ocean observatories,
which are being built on decommissioned submarine
cables to deploy an extensive fiber optic network of
sensors (cameras, wave sensors, seismometers) covering miles of ocean floor [15.13]. These cables can
also carry communication access points, very much as
cellular base stations are connected to the telephone network, allowing users to move and communicate from
places where cables cannot reach. Another example
are cabled submersibles, also known as remotely operated vehicles (ROVs). These vehicles, which may
weigh more than 10 metric tons, are connected to
a mother-ship by a cable that can extend over several
kilometers and deliver high power to the remote end,
along with high-speed communication signals. A popular example of an ROV/AUV tandem is the WHOI’s
Alvin/Jason pair of vehicles that were deployed in 1985
to discover the Titanic. Such vehicles were also instrumental in the discovery of hydro-thermal vents, sources
of extremely hot water on the bottom of deep ocean,
which revealed forms of life different from any others known previously. The first vents were found in
the late 1970s, and new ones are still being discovered. The importance of such discoveries is comparable
only to space missions, and so is the technology that
supports them. Today, vehicle technology, sensor technology, and acoustic communication technology are
mature enough to support the visionary idea of an
autonomous oceanographic sampling network [15.14].
Recent years have seen a proliferation of research
on underwater sensor networks, which we discuss in
Sect. 15.5.6.
15.3 Existing Technology
The field of underwater acoustic communication has
become fairly mature. Many commercial units are available, along with a significant number of prototypes
developed in research laboratories. The large number
of configurations available complicates the selection
process of a specific underwater acoustic modem. The
purpose of this section is to offer some guidance in
selecting an underwater acoustic modem. The authors
do not recommend any specific product, rather they
highlight what is important in the selection process.
Following this, a brief overview of typical performance
and field tests is presented.
15.3.1 System Requirements
Underwater acoustic modem users should always keep
in mind that the performance of these systems changes
dramatically depending on the application. For example, a system designed to operate at tens of kilometers
will typically have a much lower throughput than a system designed to relay data at a few hundred meters.
Also, some underwater acoustic modems are designed
to operate in a complex network, while others are designed for point-to-point communication between two
units.
The following list is by no mean exhaustive, but
covers the main factors that should be used in selecting an underwater acoustic modem:
Application: The user should always keep the application in mind when selecting an acoustic modem.
Voice communication constitutes a category of its
own, with well-proven technology specifically designed to relay intelligible voice with minimal delay
and simultaneous two-way communication capability. Acoustic modems designed for the transmission
of command-and-control messages operate more
slowly, but very reliably. Image streaming can be
achieved using the latest generation of high-bit rate
(one-way) acoustic modems. Voice communication
modems and command-and-control modems technology is much more mature than image streaming
modems.
Cost: Typically between $5,000 and $50,000 (US)
per unit, depending on the complexity and performance.
Size: Underwater acoustic modems are usually
cylindrical in shape, with a pressure vessel containing the electronics and one or multiple transducers
mounted on one end. The size varies from 0:05 m
Part B | 15.3
turbances, as well as the detection of objects on the
ocean floor, and transmission of images from remote
sites. Implicitly, wireless signal transmission is also
crucial for monitoring and control of remote instruments, and for communicating with robots and AUVs,
which can serve on isolated missions, or as parts of
a mobile network. Applications involving AUVs range
from search and survey missions to supervisory control
and collection of mapping data, be they images, video,
or side-scan sonar.
Autonomous systems are envisioned both for standalone applications and as wireless extensions to cabled
systems. For example, a stand-alone 15 kbps acoustic
link, intended to provide data transfer from bottommounted, battery-powered instruments such as seismometers to a surface buoy is described in [15.5].
A different example is that of ocean observatories,
which are being built on decommissioned submarine
cables to deploy an extensive fiber optic network of
sensors (cameras, wave sensors, seismometers) covering miles of ocean floor [15.13]. These cables can
also carry communication access points, very much as
cellular base stations are connected to the telephone network, allowing users to move and communicate from
places where cables cannot reach. Another example
are cabled submersibles, also known as remotely operated vehicles (ROVs). These vehicles, which may
weigh more than 10 metric tons, are connected to
a mother-ship by a cable that can extend over several
kilometers and deliver high power to the remote end,
along with high-speed communication signals. A popular example of an ROV/AUV tandem is the WHOI’s
Alvin/Jason pair of vehicles that were deployed in 1985
to discover the Titanic. Such vehicles were also instrumental in the discovery of hydro-thermal vents, sources
of extremely hot water on the bottom of deep ocean,
which revealed forms of life different from any others known previously. The first vents were found in
the late 1970s, and new ones are still being discovered. The importance of such discoveries is comparable
only to space missions, and so is the technology that
supports them. Today, vehicle technology, sensor technology, and acoustic communication technology are
mature enough to support the visionary idea of an
autonomous oceanographic sampling network [15.14].
Recent years have seen a proliferation of research
on underwater sensor networks, which we discuss in
Sect. 15.5.6.
15.3 Existing Technology
The field of underwater acoustic communication has
become fairly mature. Many commercial units are available, along with a significant number of prototypes
developed in research laboratories. The large number
of configurations available complicates the selection
process of a specific underwater acoustic modem. The
purpose of this section is to offer some guidance in
selecting an underwater acoustic modem. The authors
do not recommend any specific product, rather they
highlight what is important in the selection process.
Following this, a brief overview of typical performance
and field tests is presented.
15.3.1 System Requirements
Underwater acoustic modem users should always keep
in mind that the performance of these systems changes
dramatically depending on the application. For example, a system designed to operate at tens of kilometers
will typically have a much lower throughput than a system designed to relay data at a few hundred meters.
Also, some underwater acoustic modems are designed
to operate in a complex network, while others are designed for point-to-point communication between two
units.
The following list is by no mean exhaustive, but
covers the main factors that should be used in selecting an underwater acoustic modem:
Application: The user should always keep the application in mind when selecting an acoustic modem.
Voice communication constitutes a category of its
own, with well-proven technology specifically designed to relay intelligible voice with minimal delay
and simultaneous two-way communication capability. Acoustic modems designed for the transmission
of command-and-control messages operate more
slowly, but very reliably. Image streaming can be
achieved using the latest generation of high-bit rate
(one-way) acoustic modems. Voice communication
modems and command-and-control modems technology is much more mature than image streaming
modems.
Cost: Typically between $5,000 and $50,000 (US)
per unit, depending on the complexity and performance.
Size: Underwater acoustic modems are usually
cylindrical in shape, with a pressure vessel containing the electronics and one or multiple transducers
mounted on one end. The size varies from 0:05 m