DENSITY 



1976 

 J A S I O N D 



1977 



1978 



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Figure 15. — Calendar of overall POLYMODE field program. 



IDOE 78 364 

 8 78 



of temperature and pressure are transmitted on alternate days. 



To control the float depth, a block of anode quality zinc is 

 mounted externally in the seawater. This anode can be electri- 

 cally connected to the main aluminum housing via a switch 

 controlled by the pressure measurement and averaging circuit. 

 When the circuit is open, the electrochemical couple is inactive; 

 when the circuit is closed, a small saltwater battery is formed, 

 zinc goes into solution in the seawater, and the float rises about 

 2 m per day. 



POLYMODE floats are also being built with a relocation 

 and recovery subsystem for ship retrieval at sea. This is a spe- 

 cially designed, multiple-address system using 1420-Hz phase 

 encoded data transmitted from the ship to the float and received 

 via the float's low-frequency transducers. Float reply is via the 

 normal low-frequency signal. A recovery command causes a 

 7-kg external ballast weight to jettison and initiates a special 

 fast pressure telemetry cycle to verify the weight release and 

 aid recovery. 



Since 1975, 28 POLYMODE-type floats have been built and 

 used at sea. The floats have evolved from a prototype stage to 

 a more or less fixed and well-proven design that is suitable for 

 commercial fabrication. From 1975 to 1978, the following prob- 

 lems occurred: 



1) Serious damage to the floats resulted from several han- 

 dling incidents. Special handling equipment was developed to 

 avoid damage. 



2) Electronic equipment failures occurred shortly after floats 

 were launched. Thorough burn-in of the electronic equipment 

 was found to be important. Adequate time must be allowed 

 between fabrication and deployment for burn-in of electronic 

 components. 



3) Floats built commercially differed slightly from those built 

 in the lab. Careful and uniform test procedures for equipment 

 are essential to ensure an effective transition from a research 

 activity to a routine operation. 



23 



