Techniques and Technology of Exploration in the Gulf of the Farallones 



Kaye Kinoshita and John L. Chin 



Although the oceans occupy 7 1 percent of 

 the Earth's surface, they continue to be 

 largely shrouded in mystery. From the 

 surface it is impossible to see into the 

 ocean depths, and actually going into 

 those depths is both costly and hazardous. 

 Because the oceans are crucial to our 

 survival, we must try to understand the 

 interactions of their complex physical and 

 biological systems. In pursuit of this 

 understanding, scientists seek many kinds 

 of information the depth, composition, 

 temperatures, and movements of the water; 

 the shape and composition of the sea 

 bottom; and the types and abundances of 

 the animals and plants living in the water 

 and at the bottom. Some of these kinds 

 of information can be obtained at the sur- 

 face from ships, others require the low- 

 ering of cameras and sampling devices, 

 and still others are best acquired through 

 exploration in submersible vehicles, both 

 manned and unmanned. Exploration in the 

 Gulf of the Farallones has made use of a 

 wide variety of such techniques. 



When collecting multiple sets of geo- 

 physical and geological data over a wide 

 area of the sea floor, precisely determining 

 the location of an object or feature is criti- 

 cal. Navigation was therefore the common 

 denominator that linked all data types 



together in a spatial frame of reference. 

 Four types of navigation sensors were used 

 to determine the locations of objects and 

 features on the sea floor Global Position- 

 ing System (GPS) satellites, Loran-C, and 

 two ranging navigation systems (Del Norte 

 and Benthos). The output from the GPS, 

 Loran-C, and Del Norte systems was fed 

 directly into a navigation program running 

 on a microcomputer. This program pro- 

 vided important real-time location infor- 

 mation, which was relayed to computers in 

 onboard science laboratories and the ship's 

 bridge. The Benthos system was a stand- 

 alone system, which had its own program 

 and display and ran separately from the 

 integrated navigation system.- 



Two types of equipment using sound 

 waves sidescan sonar and seismic-reflec- 

 tion systems were used to map the sea 

 floor in the gulf. Images from three differ- 

 ent sidescan systems were cut and pasted 

 together to create "mosaics," which pro- 

 vide excellent map views of the area of 

 sea floor studied in the gulf. Both 3.5-kilo- 

 hertz (kHz) and 4.5-kHz high-resolution 

 seismic-reflection systems were used to 

 profile and look at the shallow subbottom 

 (uppermost 160 feet) of the sea floor. A 

 10-kHz system was also used to provide 

 accurate bathymetric information. 



A towed seabed gamma-ray spectrom- 

 eter belonging to and operated by the 

 British Geological Survey, called the EEL 

 because of its eel-like appearance, was 

 used to measure the radioactivity of the 

 sea floor. The gamma detector can measure 

 both natural and artificial radioactivity in 

 surficial sea-floor material to an effective 

 maximum subbottom depth of about a foot. 

 As the probe is towed, data are sent up the 

 towing cable to a shipboard computer and 

 recorded continuously. 



Physical samples of the sea bottom 

 were taken with two devices. A gravity 

 corer, driven into the bottom by a heavy 

 weight, was used to obtain round cores 

 about 4 inches in diameter and as much 

 as 10 feet long. This type of coring device 

 was used where the sediment was expected 

 to be soft and muddy. The other sampling 

 device used was a Van Veen grab sampler, 

 which works very much like a clam shell. 

 When the two sides of the shell touch the 

 sea floor they close and scoop up a sample. 

 This device was used where the sea floor 

 was expected to be sandy, because sand 

 would not easily be penetrated by or 

 retained in a gravity corer. 



Instrument packages were attached to 

 lines moored to the sea floor to measure 

 the velocity and direction of ocean currents 



in the Gulf of the Farallones. These instru- 

 ment packages also measured water clarity, 

 conductivity, salinity, and temperature. 



A camera sled designed and built by 

 the U.S. Geological Survey was towed 

 from a research vessel along a preplanned 

 trackline to take pictures of the sea floor in 

 the gulf. Video was recorded continuously 

 and still photographs were taken every 

 10 to 15 seconds. The images of the sea 

 floor obtained with the camera sled were 

 used to visually verify information col- 

 lected from both sidescan-sonar mapping 

 and physical sampling. 



Visual observations were also made 

 with Sea Cliff, a manned deep-submer- 

 gence vehicle (DSV) operated by the U.S. 

 Navy. Sea Cliff also had the capability 

 to take physical samples with the use of 

 mechanical arms. The Navy's unmanned 

 Advanced Tethered Vehicle (ATV) was 

 also used to obtain additional video and 

 photographs of the sea floor. The ATV can 

 be remotely "driven" to a specific site, and 

 it proved to be the most precise way used 

 so far in the Gulf of the Farallones to view 

 objects on the sea floor. 



4 Techniques and Technology of Exploration in the Gulf of the Farallones 



