e. Water Currents: (Fig. 11.5) Accurate 

 measurement of water currents from a sub- 

 mersible is conducted when the vehicle is 

 bottomed. Because ocean currents are varia- 

 ble in time and space and the submersible 

 data of veiy short time duration, the data 

 thus obtained is representative of only the 

 period and precise location of the measure- 

 ment. Inaccuracies in submersible heading 

 and speed while underwater, and the small 

 relative magnitude of currents, preclude 

 computing true from apparent current veloc- 

 ity as is done with wind velocities on ships. 

 Drifting within the current and being 

 tracked from the surface, as was BEN 

 FRANKLIN, can be a method of measure- 

 ment, but it is too expensive and restricted 

 for normal operations. Similarly, drifting and 

 measuring one's speed and direction with 

 Doppler sonar is accompanied by the same 

 restrictions. Consequently, this instrument 

 has been affixed to many submersibles owing 

 to its ease of installation and operation, and 

 its relatively low cost. 



Operation: Current speed is monitored 

 by a Savonious rotor with 10 magnets 

 equally spaced on a perimeter base. A mag- 

 netic switch counts the pulses per time inter- 

 val and the speed is registered on a taut 

 band meter such that 83.5 rpm equal 1 knot. 

 Current direction is sensed by a vane which 

 is connected magnetically to a compass. Al- 

 lowable inclination from the vertical is 20 

 degrees. 



Data: (Hydro Products Model) Absolute 

 current speed (in knots) and direction (rela- 

 tive to magnetic north) are graphed continu- 

 ously with time. 



Current Speed: 0.1-6.0 knots ±2% 

 Current 



Direction: 0-360 degrees ±7 



Bottom 



Ocean bottom information is required for a 

 variety of reasons. For example, to design, 

 install and maintain cables, the following 

 bottom and near bottom information is re- 

 quired: Nature and size of bottom materials, 

 slope, strength, presence of artifacts (wrecks, 

 cables, pipelines), sediment stability, cur- 

 rents and, if the cable is to be buried or 

 plowed under, whether or not solid rock out- 



crops or horizons underlay an apparently 

 soft ocean floor which may prohibit plowing. 

 While BEN FRANKLIN carried no bottom 

 sampling instruments on its drift mission, 

 such capability is mandatory for a surveying 

 submersible. Hence, various bottom sam- 

 pling devices will be included in this section 

 and will serve to represent those capabilities 

 developed for research and engineering. 



a. Stereophotography System: (Fig. 11.6) 

 Operation: To obtain the widest possi- 

 ble coverage, two cameras and two strobes 

 were mounted in tandem with only minimum 

 overlap of their fields of view. Stereo pairs 

 are achieved by overlapping successive pho- 

 tographs in each camera. Each side can be 

 fired in sviccession or independently. Each 

 camera is pre-focused so that the bottom can 

 be photographed at ranges from 15 to 50 feet. 

 The minimum time between exposures for 

 each camera is 4 seconds. 



Data: (EG&G Model 207) This system 

 can supply 3,300 stereo-pair photographs of 

 the sea floor without reloading. 



Adjustments: f/4.5 to f/22; 1/10-1/200 sec. 



Exposure rate: 4, 6, 8, 10, 12, and 24 

 seconds and manual. 



b. Side Scan Sonar: (Fig. 11.7) 

 Operation: Each transducer emits a 



0.1-millisecond, 110-kHz pulse at a regular 

 interval (0.1, 0.2, or 0.4 sec). The beam pat- 

 tern is only 1 degree in the horizontal plane 

 but approaches 60 degrees in the vertical 

 plane. As the submersible advances, echoes 

 from acoustic reflectors in the insonified 

 area are recorded on a strip chart. 



Data: (EG&G Model) The acoustic map 

 resulting from this sonar provides a three- 

 dimensional facsimile of the prominent relief 

 features on both sides of the submersible's 

 path to ranges of 250, 500 or 1,000 feet. 

 Resolution of 1/250 of full scale is normally 

 realized. 



c. Subbottom Profiling: (Fig. 11.8) 

 Operation: The transducer emits a 



pulse of no less than 105 decibels (on axis) of 

 5-kHz acoustic energy in a 50-degree beam 

 towards the bottom. Portions of this pulse 

 are reflected at each interface encountered 

 and these echoes are picked up as they ar- 

 rive back at the transducer. A synchronized 

 blade on the recorder registers the arrival of 

 each echo on wet recording paper. The sweep 



548 



