The Profiling Autonomous Lagrangian Current Explorer (PALACE) floats are used to provide information on both the current circulation at a predetermined depth and the temperature structure in the upper layers of the ocean. The floats are designed to float on the surface for 24 hours and then submerge to a depth of 1000 decibars and remain there for 10 days. They then rise to the surface and measure the water temperature approximately every 10 decibars to obtain a temperature profile. While on the surface the data is transmitted to the Service ARGOS satellite system. From the Doppler frequency shift of the transmitted signal as it is received by the stellite, the geographic position of the float can be computed. This cycle, 24 hours on the surface and 10 days at depth is then repeated for the life of the float. Barring a failure of any components, the floats have sufficent battery capacity to operate for over two years.
The floats have an aluminum hull, approximately 6" in diameter by 60" long, with an antenna for data transmission to the satellite system. The antenna and a temperature probe are mounted on the top end of the float and a pressure sensor is ported to the ocean near the bottom end cap. A damper plate is attached near the top to stabilize the float in the surface wave field.
To control the buoyancy of the float, a small amount of oil is contained within the float. When the float is submerged, all of the oil is kept entirely within the hull. When it is time to rise to the surface, the oil is pumped into an external rubber bladder which expands. Since the weight of the float does not change, but its volume increases when the bladder expands, the float becomes more buoyant and floats to the surface. Similarly, when the float is on the surface and it is time to submerge, the oil is withdrawn from the bladder into the hull of the float and the buoyancy decreases. Oil is pumped into the bladder by a small high pressure electric pump. When the float is built, the air pressure in the hull is evacuated to about a 0.5 atmosphere vacuum. By opening a valve, the oil is then sucked out of the external bladder into the hull when it is time to submerge. The depth to which the gloat submerges is controlled by very carefully ballasting it when it is built. Typically the weight of the float is about 25000 grams and must be accurate to within a few grams. A one gram error results in a depth error of about 19 meters.
Deployment procedures typically include removing the PALACE floats from the shipping crates and inspecting for damage, starting the self test several hours before deployment (2-7 hours for the WHOI floats and 5-12 hours for the AOML floats) and installing the stability disk. Once the self test has been successfully completed the PALACE float is deployed by lowering off the stern of the ship while the ship steams slowly at 1-2 knots.
AOML PALACE were equipped to begin ARGOS transmissions within 2 hours from start up. For these floats a further test of the transmission system was performed by allowing the PALACE to cycle through one complete start up (6 hours) prior to deployment. The PALACE was then reset at least two hours before deployment. This allowed shore based personnel at AOML to verify ARGOS transmissions were being received.
The PALACE floats deployed along 6oN included a conductivity sensor and were ballasted for approximately 800 meters. Ray Schmitt (WHOI) can supply the operational details for these floats. The floats along the equator and 6oS (AOML) included only a temperature sensor, except for the float deployed at 0, 38W which also included a salinity sensor. The AOML floats have been ballasted to rest at a density of 1032.078 kg/m**3, which is approximately 1000 meters at these latitudes. AOML float deployment information is summarized in Attachment 1.
All the floats deployed along the equator have gone through at least one cycle, except for one. The floats deployed along 6oS are beginning to surface.
Table 4 (from the Cruise Report): PALACE floats deployed
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