Contributions to Global Ocean Observations
59
bladder, raising the vehicle’s volume and buoyancy to ascend. Oil returned inside the
pressure case to descend. Webb began developing a float using this buoyancy engine
while, at the same time, SIO addressed the problem of keeping the antenna on a
marginally buoyant vehicle above the surface in significant sea states.
WOCE
The World Ocean Circulation Experiment (WOCE) was the first oceanographic program to address the general circulation using global observations by the international
community. The objective of WOCE was to significantly increase knowledge
of the ocean’s circulation by combining a global hydrographic survey, satellite
measurements of sea-surface height, and global mapping of ocean velocity using
drifters, floats, and high-density moored arrays all integrated by dynamical and inverse models. Float measurements near 1 km depth were to provide a level of known
motion for referencing geostrophic shear maps, freeing inverse models to address
key processes like turbulent mixing. The surface and float observations were the first
sustained direct velocity observations taken to a global scale.
Three developments made possible the bold WOCE plan to directly measure
circulation on two levels. First, Peter Niiler’s (1987) group had developed a surface
drifter that was shown to have minimal wind- and wave-driven slip through the water at
its drogue. The design was unique from predecessors in two ways. The drogue is very
much larger than the surface float, minimizing forces applied by winds and waves.
This was made possible by using a small surface float that supported electronics and
antenna for Argos tracking and a small intermediate float that in operation was usually
submerged.
Second, the development by Tom Rossby and Don Dorson of the RAFOS float
made feasible deployment of large arrays of acoustically tracked floats. The principle
was simple: invert the SOFAR system (and name) using a few large sound sources
and many relatively small and inexpensive quasi-Lagrangian floats that function as
acoustic receivers. The floats record the times signals are received and, at the end of
their life, pop to the surface to transmit these times through satellite. These 1.5-m-long
floats have a mass of about 10 kg, simplifying deployment. The pressure case is a
glass tube, minimizing manufacturing cost and matching thermal expansion to that of
seawater. This, coupled with a spring-backed piston “compressee” to increase float
compressibility to near that of seawater, gives the RAFOS float properties close to
seawater so it approximately follows a water parcel. The initial sound sources were
essentially moored SOFAR floats that could be deployed from volunteer ships but
more efficient sources were soon developed. With a tracking range comparable to
SOFAR floats, the low cost of RAFOS floats made it feasible to deploy large numbers
of floats in an area and track them for times of order 1 year.
Third, the SIO–Webb collaboration led to development of the Autonomous
Lagrangian Circulation Explorer (ALACE; Davis et al., 1992). It was field tested
59
bladder, raising the vehicle’s volume and buoyancy to ascend. Oil returned inside the
pressure case to descend. Webb began developing a float using this buoyancy engine
while, at the same time, SIO addressed the problem of keeping the antenna on a
marginally buoyant vehicle above the surface in significant sea states.
WOCE
The World Ocean Circulation Experiment (WOCE) was the first oceanographic program to address the general circulation using global observations by the international
community. The objective of WOCE was to significantly increase knowledge
of the ocean’s circulation by combining a global hydrographic survey, satellite
measurements of sea-surface height, and global mapping of ocean velocity using
drifters, floats, and high-density moored arrays all integrated by dynamical and inverse models. Float measurements near 1 km depth were to provide a level of known
motion for referencing geostrophic shear maps, freeing inverse models to address
key processes like turbulent mixing. The surface and float observations were the first
sustained direct velocity observations taken to a global scale.
Three developments made possible the bold WOCE plan to directly measure
circulation on two levels. First, Peter Niiler’s (1987) group had developed a surface
drifter that was shown to have minimal wind- and wave-driven slip through the water at
its drogue. The design was unique from predecessors in two ways. The drogue is very
much larger than the surface float, minimizing forces applied by winds and waves.
This was made possible by using a small surface float that supported electronics and
antenna for Argos tracking and a small intermediate float that in operation was usually
submerged.
Second, the development by Tom Rossby and Don Dorson of the RAFOS float
made feasible deployment of large arrays of acoustically tracked floats. The principle
was simple: invert the SOFAR system (and name) using a few large sound sources
and many relatively small and inexpensive quasi-Lagrangian floats that function as
acoustic receivers. The floats record the times signals are received and, at the end of
their life, pop to the surface to transmit these times through satellite. These 1.5-m-long
floats have a mass of about 10 kg, simplifying deployment. The pressure case is a
glass tube, minimizing manufacturing cost and matching thermal expansion to that of
seawater. This, coupled with a spring-backed piston “compressee” to increase float
compressibility to near that of seawater, gives the RAFOS float properties close to
seawater so it approximately follows a water parcel. The initial sound sources were
essentially moored SOFAR floats that could be deployed from volunteer ships but
more efficient sources were soon developed. With a tracking range comparable to
SOFAR floats, the low cost of RAFOS floats made it feasible to deploy large numbers
of floats in an area and track them for times of order 1 year.
Third, the SIO–Webb collaboration led to development of the Autonomous
Lagrangian Circulation Explorer (ALACE; Davis et al., 1992). It was field tested