THE NEAR-SURFACE LAYER OF THE OCEAN
During TOGA COARE, a free-rising profiler connected with the
“shuttle” (winged frame) was deployed from the stern of the R/V Moana
Wave with help of a metal frame, which allowed the device to slide from the
ship into the water (Figure 3-5c). After leaving the metal frame, the profiler
fell into the water and slid outside the ship’s wake a distance of about 15 to
35 meters as it sank (Figure 3-4). This distance depended on the drift of the
ship and the intensity of near-surface currents. Normally at 20-m depth the
pressure release mechanism released the profiler from the shuttle and the
profiler turned to a vertical orientation. The profiler then ascended to the
surface with a vertical velocity of 2 to 3 m s
-1 , depending on the net
buoyancy of the profiler. The rather large net buoyancy-to-weight ratio of
the profiler provided nearly constant vertical speed with respect to the
surrounding water mass (see Section 3.2.4). Studies of the temperature,
salinity, and density profiles in the near-surface layer of the ocean with the
free-rising profiler are described in Chapter 4.
b) Bow probes
Bow probes included the electrical conductivity, temperature and
pressure (ECTP) probe and the electromagnetic velocity and acceleration
(EMVA) probes (Figure 3-5a). The EMVA sensor, originally developed for
use on submarines, had a hydrodynamic form and a low hydrodynamic noise
level. This probe is a linear device for a wide flow-speed range (0 - 12.5
m/s); the spatial resolution is about 1 cm. According to laboratory tests, the
electronic noise level of the velocity sensor in the frequency range 2 Hz -
400 Hz was equivalent to 0.8 mm s
-1 . More details about the EMVA probe
and the ECTP probes can be found in Soloviev et al. (1998; 1999).
A special metal frame was designed to install these probes on the bow of
the vessel (Figure 3-5b and Figure 3-6). The mean depth of the sensors was
about 1.7 m, which varied slightly during the cruise, depending on the levels
of the ship’s fuel and water tanks, and the ship speed.
The pressure wave in front of a moving ship can result in a rapid flow
distortion (Fornwalt et al., 2002). From classical hydrodynamics it is known
that the flow in front of a moving sphere is significantly disturbed within
approximately 3 radii of the sphere (Van Dyke, 1982). To reduce
disturbances by ship’s hydrodynamics, a vessel with a sharp-angled hull
should be used. At the level of the sensors, the angle of the hull of the R/V
Moana Wave was +/-15
o and the curvature radius of the bow tip was about
0.2 m. The pressure wave therefore concentrated within a distance of
approximately 0.6 m ahead of the hull. The bow frame (Figure 3-6)
positioned the sensor system at a distance of 2 m from the ship’s hull,
therefore, placing it outside the zone of most intense pressure disturbance.
160
During TOGA COARE, a free-rising profiler connected with the
“shuttle” (winged frame) was deployed from the stern of the R/V Moana
Wave with help of a metal frame, which allowed the device to slide from the
ship into the water (Figure 3-5c). After leaving the metal frame, the profiler
fell into the water and slid outside the ship’s wake a distance of about 15 to
35 meters as it sank (Figure 3-4). This distance depended on the drift of the
ship and the intensity of near-surface currents. Normally at 20-m depth the
pressure release mechanism released the profiler from the shuttle and the
profiler turned to a vertical orientation. The profiler then ascended to the
surface with a vertical velocity of 2 to 3 m s
-1 , depending on the net
buoyancy of the profiler. The rather large net buoyancy-to-weight ratio of
the profiler provided nearly constant vertical speed with respect to the
surrounding water mass (see Section 3.2.4). Studies of the temperature,
salinity, and density profiles in the near-surface layer of the ocean with the
free-rising profiler are described in Chapter 4.
b) Bow probes
Bow probes included the electrical conductivity, temperature and
pressure (ECTP) probe and the electromagnetic velocity and acceleration
(EMVA) probes (Figure 3-5a). The EMVA sensor, originally developed for
use on submarines, had a hydrodynamic form and a low hydrodynamic noise
level. This probe is a linear device for a wide flow-speed range (0 - 12.5
m/s); the spatial resolution is about 1 cm. According to laboratory tests, the
electronic noise level of the velocity sensor in the frequency range 2 Hz -
400 Hz was equivalent to 0.8 mm s
-1 . More details about the EMVA probe
and the ECTP probes can be found in Soloviev et al. (1998; 1999).
A special metal frame was designed to install these probes on the bow of
the vessel (Figure 3-5b and Figure 3-6). The mean depth of the sensors was
about 1.7 m, which varied slightly during the cruise, depending on the levels
of the ship’s fuel and water tanks, and the ship speed.
The pressure wave in front of a moving ship can result in a rapid flow
distortion (Fornwalt et al., 2002). From classical hydrodynamics it is known
that the flow in front of a moving sphere is significantly disturbed within
approximately 3 radii of the sphere (Van Dyke, 1982). To reduce
disturbances by ship’s hydrodynamics, a vessel with a sharp-angled hull
should be used. At the level of the sensors, the angle of the hull of the R/V
Moana Wave was +/-15
o and the curvature radius of the bow tip was about
0.2 m. The pressure wave therefore concentrated within a distance of
approximately 0.6 m ahead of the hull. The bow frame (Figure 3-6)
positioned the sensor system at a distance of 2 m from the ship’s hull,
therefore, placing it outside the zone of most intense pressure disturbance.
160