Analysis and processing also requires the acoustic data to be tagged with the
relevant navigation data (i.e., every data point is associated with the geographic
information and vessel positioning attributes). This step is typically accomplished
in real time while data are being acquired by means of synchronizing input from
several sensors (e.g., DGPS and gyrocompass) in the data collection computer.
These data are evaluated to remove any positional outliers observed while plotting
the navigation lines to verify the geometry and confirm proper operation of the
navigation instrument. Data also have to be adjusted for the variations of the sound
speed profile using the data from a CTD, XBT, or other device used for measuring
the sound speed in the water column. And the data have to be corrected for tide
variations over the time of the survey. This tide correction can be done using
harmonic tide predictions, like the ones supplied by the British Admiralty Manual,
or achieved using a software program to generate tide corrections from manual
observations, from high-low water times and heights, or from published tide data
for the given area. A more accurate tide correction can be achieved by employing
an actual tide gauge located at the survey site and/or by using an RTK GPS during
data collection.
8.3 Applications of Acoustics
Active as well as passive acoustics are amongst the most commonly used applications in the marine sciences. In the marine geosciences, applications are found in
mapping sediment transport, sediment classification, particle sizing, seafloor
mapping, sub-bottom profiling and, in the very long frequencies, the detection of
seismic events. In oceanography, the classical applications of acoustics are current
measurements, wave measurements and the study of water properties using
acoustic tomography (Medwin and Clay 1998). In marine biology, active acoustics
are used for benthos detection (such as the mapping of submerged aquatic vegetation), and for the detection of plankton and fish in concert with stock assessments
and population studies. Passive acoustics are becoming increasingly common for
the tracking and identification of marine mammals and fish. In the commercial
field, acoustics are staples for bathymetry and fish detection (a full gradient of
sophistication exists from recreational depth-sounders and fish finders to surveygrade equipment), object detection, subsurface characterization for mineral
resources, description of current and sediment/pollutant transport patterns, and
many more.
The following examples are centered on acoustic applications related to the
surrounding environment, while Chaps. 9 and 10 discuss acoustic systems used for
benthic detection and classification in some detail.
8 Acoustic Methods Overview
207
relevant navigation data (i.e., every data point is associated with the geographic
information and vessel positioning attributes). This step is typically accomplished
in real time while data are being acquired by means of synchronizing input from
several sensors (e.g., DGPS and gyrocompass) in the data collection computer.
These data are evaluated to remove any positional outliers observed while plotting
the navigation lines to verify the geometry and confirm proper operation of the
navigation instrument. Data also have to be adjusted for the variations of the sound
speed profile using the data from a CTD, XBT, or other device used for measuring
the sound speed in the water column. And the data have to be corrected for tide
variations over the time of the survey. This tide correction can be done using
harmonic tide predictions, like the ones supplied by the British Admiralty Manual,
or achieved using a software program to generate tide corrections from manual
observations, from high-low water times and heights, or from published tide data
for the given area. A more accurate tide correction can be achieved by employing
an actual tide gauge located at the survey site and/or by using an RTK GPS during
data collection.
8.3 Applications of Acoustics
Active as well as passive acoustics are amongst the most commonly used applications in the marine sciences. In the marine geosciences, applications are found in
mapping sediment transport, sediment classification, particle sizing, seafloor
mapping, sub-bottom profiling and, in the very long frequencies, the detection of
seismic events. In oceanography, the classical applications of acoustics are current
measurements, wave measurements and the study of water properties using
acoustic tomography (Medwin and Clay 1998). In marine biology, active acoustics
are used for benthos detection (such as the mapping of submerged aquatic vegetation), and for the detection of plankton and fish in concert with stock assessments
and population studies. Passive acoustics are becoming increasingly common for
the tracking and identification of marine mammals and fish. In the commercial
field, acoustics are staples for bathymetry and fish detection (a full gradient of
sophistication exists from recreational depth-sounders and fish finders to surveygrade equipment), object detection, subsurface characterization for mineral
resources, description of current and sediment/pollutant transport patterns, and
many more.
The following examples are centered on acoustic applications related to the
surrounding environment, while Chaps. 9 and 10 discuss acoustic systems used for
benthic detection and classification in some detail.
8 Acoustic Methods Overview
207