Non-Acoustic Sensors 18.5 Physical Sensor Systems 433
Part B | 18.5
temperature, pressure, and physical property sensors.
Consequently, there are more examples for these types
of sensors than those in other areas [18.28]. Classical
depth or pressure measurements in the ocean (highlighted earlier in this section) are a direct example of the
progression of physical sensors. These developments as
state-of-the-art changes are more evolutionary and usually are not revolutionary steps in progress. Water column measurements are of utmost importance to better
understand ocean processes by setting the normal background conditions and, for instance, are required to perform tsunami wave detection. A specific example is the
work on the reinforced piezoresistive pressure sensor,
which employed double diaphragms with a Wheatstone
bridge. The double diaphragm design achieved higher
sensitivity, a wider operating range, and better temperature compensation for ocean depth measurements
compared to conventional single diaphragm piezoresistive designs [18.29].
For AUV mounted current metering, one cannot
avoid the strength of acoustics to deliver flow information. Acoustic current Doppler profilers (ACDPs)
are available currently for roving current observations.
Modern ADCPs are also employed as acoustic Doppler
velocimeters (ADVs) looking at over ground velocities, and when using a specific configuration the water
velocities can be estimated while the vehicle is flying
mid water. The advancement of AUV adaptive oceanographic sensor networks, combined with 2-D and 3-D
imaging techniques, should be able to assist in mapping the fluxes across scales in environmental volumes
and interfaces. For example, atmospheric turbulence
sensing requires 3-D flow field measurements that are
within 10 cm of the air–water interface; the sensors
must be environmentally robust for persistent observations and be accurate to 0:1 cm s
1 . Water column
sensing requires 3-D flow field levels quantified within
5% throughout the water column to better understand
the turbulent transport and flux of gases.
Transport in the water column includes chemicals
as well as biomass in water and at the water–air interface. Combining optical and acoustics sensors on
mobile platforms may provide some of the functionality
needed for simultaneously measuring ocean chemistry
and biology across a variety of scales. As physical sensors have advanced in moored ocean observatories over
the last decade, one should see opportunities to transfer the sensing functions onto AUVs. Modifications will
be needed in areas of computation, power, and packaging to accommodate the unique features of mobile
platforms.
Instruments to quantify the relationship between
turbulence in water coupled with turbulence in the air
directly above would provide major changes in physical oceanographic observations. This requires surface
sensors for fluxes through the sea surface interface.
To accomplish these turbulence goals, new capabilities for AUVs that advance mapping of 3-D flow field
(transport, fluid velocity) systems are one focus, as well
as microturbulence sensors. Standardization for field
physical sensing devices will be required on AUVs,
just as it has been on observatories and drifters. Continued miniaturization in physical sensors, electronics,
and packaging will be driven by new unmanned system designs. A new area of rising research interest is
the discrimination of nanoparticles and aerosols, manmade and naturally occurring. Particle size distribution
and shape sensors with near real-time response for
mobile surveys are areas in need of development for
AUV-based event response. Sensor systems must be
able to accurately establish the sensor/AUV orientation
within the environment. Physical location and altitude
is the largest uncertainty in mobile hydrological observations as one example. As submersible robots become
increasingly available, knowledge of their exact position in four dimensions will become more and more
critical. An error of alignment within ˙0:1 degrees or
0:5 cm will substantially degrade the utility of bio-geochemical observations.
Multi-parameter systems are commercially available (DO, pH, ORP, chlorophyll, rhodamine, turbidity,
conductivity, temperature, salinity, specific conductivity, depth) and inclusion of these is becoming the backbone of AUV deployments; we expect this to expand in
the future. Mini bio-optics packages: chlorophyll, beam
transmittance, angular scattering, conductivity, temperature, depth etc., are available and further expand the
ocean optics and bio-optical data streams. Maps generated with these data parameters will provide richer
physio-chemical information sets to real-time circulation models and fisheries management. Greater optical
sensing capability can be expected in both the spectral and imaging realms. Using imaging technologies
from micrometer to the meter scale is and will further improve details on particles of benthic biota and
fish [18.30, 31].
Several instruments for optical detection are already available; this is not a complete list and new
developments are underway. A number of existing instruments have already been successfully adapted to
AUVs. Sensors for bioluminescence, particle counting
and imaging are available off the shelf from a number
of manufacturers.
The underwater bioluminescence assessment tool
(UBAT) from Wet Labs provides measurements of
mechanically stimulated bioluminescence of continuously flowing samples for potential bioluminescence in
units of photon per second per liter. UBAT is a small
Part B | 18.5
temperature, pressure, and physical property sensors.
Consequently, there are more examples for these types
of sensors than those in other areas [18.28]. Classical
depth or pressure measurements in the ocean (highlighted earlier in this section) are a direct example of the
progression of physical sensors. These developments as
state-of-the-art changes are more evolutionary and usually are not revolutionary steps in progress. Water column measurements are of utmost importance to better
understand ocean processes by setting the normal background conditions and, for instance, are required to perform tsunami wave detection. A specific example is the
work on the reinforced piezoresistive pressure sensor,
which employed double diaphragms with a Wheatstone
bridge. The double diaphragm design achieved higher
sensitivity, a wider operating range, and better temperature compensation for ocean depth measurements
compared to conventional single diaphragm piezoresistive designs [18.29].
For AUV mounted current metering, one cannot
avoid the strength of acoustics to deliver flow information. Acoustic current Doppler profilers (ACDPs)
are available currently for roving current observations.
Modern ADCPs are also employed as acoustic Doppler
velocimeters (ADVs) looking at over ground velocities, and when using a specific configuration the water
velocities can be estimated while the vehicle is flying
mid water. The advancement of AUV adaptive oceanographic sensor networks, combined with 2-D and 3-D
imaging techniques, should be able to assist in mapping the fluxes across scales in environmental volumes
and interfaces. For example, atmospheric turbulence
sensing requires 3-D flow field measurements that are
within 10 cm of the air–water interface; the sensors
must be environmentally robust for persistent observations and be accurate to 0:1 cm s
1 . Water column
sensing requires 3-D flow field levels quantified within
5% throughout the water column to better understand
the turbulent transport and flux of gases.
Transport in the water column includes chemicals
as well as biomass in water and at the water–air interface. Combining optical and acoustics sensors on
mobile platforms may provide some of the functionality
needed for simultaneously measuring ocean chemistry
and biology across a variety of scales. As physical sensors have advanced in moored ocean observatories over
the last decade, one should see opportunities to transfer the sensing functions onto AUVs. Modifications will
be needed in areas of computation, power, and packaging to accommodate the unique features of mobile
platforms.
Instruments to quantify the relationship between
turbulence in water coupled with turbulence in the air
directly above would provide major changes in physical oceanographic observations. This requires surface
sensors for fluxes through the sea surface interface.
To accomplish these turbulence goals, new capabilities for AUVs that advance mapping of 3-D flow field
(transport, fluid velocity) systems are one focus, as well
as microturbulence sensors. Standardization for field
physical sensing devices will be required on AUVs,
just as it has been on observatories and drifters. Continued miniaturization in physical sensors, electronics,
and packaging will be driven by new unmanned system designs. A new area of rising research interest is
the discrimination of nanoparticles and aerosols, manmade and naturally occurring. Particle size distribution
and shape sensors with near real-time response for
mobile surveys are areas in need of development for
AUV-based event response. Sensor systems must be
able to accurately establish the sensor/AUV orientation
within the environment. Physical location and altitude
is the largest uncertainty in mobile hydrological observations as one example. As submersible robots become
increasingly available, knowledge of their exact position in four dimensions will become more and more
critical. An error of alignment within ˙0:1 degrees or
0:5 cm will substantially degrade the utility of bio-geochemical observations.
Multi-parameter systems are commercially available (DO, pH, ORP, chlorophyll, rhodamine, turbidity,
conductivity, temperature, salinity, specific conductivity, depth) and inclusion of these is becoming the backbone of AUV deployments; we expect this to expand in
the future. Mini bio-optics packages: chlorophyll, beam
transmittance, angular scattering, conductivity, temperature, depth etc., are available and further expand the
ocean optics and bio-optical data streams. Maps generated with these data parameters will provide richer
physio-chemical information sets to real-time circulation models and fisheries management. Greater optical
sensing capability can be expected in both the spectral and imaging realms. Using imaging technologies
from micrometer to the meter scale is and will further improve details on particles of benthic biota and
fish [18.30, 31].
Several instruments for optical detection are already available; this is not a complete list and new
developments are underway. A number of existing instruments have already been successfully adapted to
AUVs. Sensors for bioluminescence, particle counting
and imaging are available off the shelf from a number
of manufacturers.
The underwater bioluminescence assessment tool
(UBAT) from Wet Labs provides measurements of
mechanically stimulated bioluminescence of continuously flowing samples for potential bioluminescence in
units of photon per second per liter. UBAT is a small