magnetic north. This was acconrplished by attaching a bar magnet to 

 the frame of the current meter near the housing for the compass 

 (Figure 9)« The compass in the current meter now used the bar mag- 

 net as a north reference. The bar magnet and the ctirrent meter were 

 aligned to a true north reference (provided by the Air Force Geo- 

 detic Survey Team) by means of sections of rigid pipe attached to 

 the current meter as it was lowered into the water. 



The vmderwater camera and electronic flash combination that was 

 used to obtain the sea-flooj" photographs was a model-205 camera and 

 model-206 light source (Figure 10 ), manufactured by E.G.& G. Inter- 

 national, Inc. These units were movinted in a steel protective frame- 

 work which was designed to fit through a two-foot diameter hole. A 

 bottom sensing trigger weight was used to activate the camera and 

 flash combination at the proper distance (8 feet) above the sea floor. 



The camera utilizes an F/4.5 lens especially designed for under- 

 water use. It was mounted on the frame so as to point at the sea 

 floor at a 4o degree angle with the vertical. The angular dimensions 

 covered by the optical system in the camera itself are such as to pro- 

 vide 58 degree coverage on the short side of the rectangular photo- 

 graph and 51 degree coverage on the long side of the rectangular 

 photograph. 



The camera is loaded with standard 55inm film in a 56 exposure 

 cassette. Twenty two exposvires can be obtained during a lowering. 

 The film used during this s-urvey was Kodak plus X. The flash uses 

 a Xenon light; therefore, the spectrum produced is similar to that 

 of sunlight. 



Operation of the camera and light source is accomplished by the 

 closing of the bottom sensing switch. Momentary actuation of this 

 switch causes the shutter to open, triggering the light source. 

 Immediately after the exposure has been made, the film is automati- 

 cally advanced to the next frame in about 2 to ^ seconds, depending 

 on the condition of the battery. 



During this stirvey, the camera and flash combination was lowered 

 until the trigger weight touched the sea floor. It was then repeat- 

 edly raised and lowered a distance of approximately 20 feet off the 

 sea floor, allowing 30 seconds between lowerings to double insure 

 that the flash capacitors were charged to maximum energy. 



The feasibility of through-the-ice echo sounding was investi- 

 gated using an E.G.& G. Model-25i^ Continuous Seismic Profiling Sys- 

 tem, which HAVOCEAWO happened to have on hand. The system operates 

 at an acoustic frequency of 12 kilocycles and has a high peak power 

 output (about 105 db//l dyne /cm^), short pulse length (about 0.1 

 millisecond), and high repetition rate (lO or 20 pulses per second). 

 The entire system consists of three separate physical components: 

 (1) a recorder/driver console, (2) a transmitter/receiver transducer, 



323 



