Keller 35 and the Sigma by Inderbitzen. 36 These corers have the desirable 

 feature of a larger diameter than the others, but the flexibility of the plastic 

 core barrel prevents their taking long samples. The study of coring techniques 

 for engineering purposes performed by Richards and Parker 21 will aid in the 

 selection of corer type for use in a given application. 



Corers using driving techniques other than gravity also have been 

 developed. Gas-propelled corers include the Gas Operated Sea Floor Sampler 37 

 and the Free Fall Rocket Corer. 38 The DIVCOR developed by DIVCON, Inc. 

 of Houston uses a bottom-sitting platform with a drilling technique to penetrate 

 the sediment. This device has a 600-foot water depth limitation at the present 

 time. Corers utilizing vibratory action as a driving means include the VI BRO- 

 CORE 39 and the VIBRA-CORER. 40 



From studying the capabilities of present equipment, it is concluded 

 that a new coring system is required. The new system should utilize a bottom 

 sitting platform to enable taking incremental samples of the sediment column 

 and should be capable of deeper penetration of the sediments than is now 

 attainable with gravity-driven samplers. This sampler also should be capable 

 of functioning in the deep ocean. Accordingly, NCEL is developing such a 

 corer system based on an automated drill rig concept. 



The development of the NCE L automated drill rig corer is currently 

 in the final design stage. When completed, the corer will have the capability 

 to take relatively undisturbed incremental samples 3 inches in diameter and 

 5 feet long from sediment depths to 50 feet in water depths to 6,000 feet. 

 The corer will be capable of sampling primarily cohesive sediments. The 

 coring system will be composed of the submersible automated drill rig which 

 will rest on the seafloor during sampling operations, a coaxial load/power 

 cable, winch, power supply, and a control console. 



Positioning Systems 



The techniques used for determining positions at sea include electronic, 

 acoustic, laser, and visual systems. Each system has its particular applications 

 and limitations. The most commonly used technique is the electronic. The 

 laser and visual systems are limited to line-of-sight surveys; thus, applications 

 are limited to near-shore areas. Instruments using these techniques will now 

 be discussed. 



Table B-2 is a listing of electronic positioning systems that may be 

 suitable for use in a particular survey problem. This listing is based on the 

 information presented by Ferrara 41 in his report on electronic positioning 

 systems for surveyors. As indicated in this table, there are some limitations 

 to each of the systems. Differences in atmospheric conditions at different 

 times cause errors in observed positions. Intervening land and objects interfere 



38 



