UNTENDED DIGITAL DATA ACQUISITION SYSTEM PHILOSOPHY 



A. R. METZLER 



Marine Advisers, Inc. 



La Jolla, California 



INTRODUCTION 



Data gathering in the ocean as well as in the 

 air-land interfaces of the ocean has been 

 approached in many different ways in the past sev- 

 eral years . The prime method in the past has been 

 to take the scientist to the scene of his problem 

 via surface vessels and collect data in this man- 

 ner. It is certain that this philosophy will 

 never be replaced but the advent of new tools 

 based on later developments are slowly coming to 

 the aid of the thinly spread scientist. It is 

 therefore a natural development for the oceano- 

 graphic community to think in terms of untended 

 data gathering systems placed in the areas of 

 interest for the particular problem concerned. 

 There is the very important economic factor con- 

 cerning the logistics support that has to be 

 given to the scientist while in the field. 

 Another factor of concern is the speed with which 

 present day oceanography would like to move ahead 

 in methods of data collection and presentation. 

 These general problems primarily seem to be 

 responsible for the present tendency of the field 

 to turn toward systems approaches to the collec- 

 tion of oceanographic data. 



The system approach to be outlined here is 

 merely the collection of several different talents 

 and techniques to perform the aims of satisfying 

 what we might consider as the latest methods of 

 data collection. Marine Advisers, Inc. in asso- 

 ciation with Ocean Research Equipment, Inc. has 

 designed the system for unattended operation for 

 periods up to h months with a capacity of record- 

 ing up to l/3 of a million complete data samples 

 from a variety of individual sensors . 



GENERAL FEATURES OF THE SYSTEM 



The underwater system is diagrammatically 

 shown in Fig. 1. This is a 2-buoy taut-wire 

 mooring system designed for relatively shallow 

 work. Below the surface buoy with its included 

 meteorological sensors is a slack painter down 

 to the subsurface buoy. This subsurface buoy 

 with included data logging system is moored 

 between 30 and 60 feet from the surface. Below 

 the subsurface buoy is the sensor chain down to 

 the anchor assembly. 



The entire data logging system and power sup- 

 ply are located in the subsurface buoy as 



previously mentioned. The mooring lines and 

 electrical cables are one and the same in that the 

 strain members are located within the electrical 

 cable from the slack painter down to the last 

 sensor . On the first mooring attempt the system 

 was placed in 150 feet of water with the subsur- 

 face buoy 30 feet below the surface. 



Each underwater sensor unit in this diagram 

 consists of a Savonius rotor current meter, a 

 direction vane (referenced to a magnetic compass 

 in each sensor) and a temperature probe. Each 

 sensor is hard wire connected to the data gather- 

 ing package on the subsurface buoy. In the 

 present system there is an anemometer and a wind 

 direction sensor on the surface buoy (Fig. 2) and 

 these are also referenced to a magnetic compass . 

 The buoys are foam filled fiberglass with an 

 outer Gel-coat and a polyvinyl-chloride (surface 

 unit) or aluminum (subsurface unit) central tube. 

 Internally, the surface buoy contains only the 

 batteries and flashing unit for the navigation 

 lights. This buoy also serves as a junction box 

 for the meteorological sensor wires going down to 

 the subsurface package as well as a series of 

 12 data lines coming to the surface buoy from the 

 subsurface buoy. With this arrangement a small 

 readout box can be plugged into the surface buoy 

 from a small boat to read the data at the same 

 time and with the same precision as it is being 

 fed to the magnetic tape recording unit in the 

 subsurface buoy. 



Three such underwater sensor units were used 

 for the first series of tests . The system as it 

 is presently designed has the capability of at 

 least 10 such sensors in the chain. There is a 

 length of polypropylene line between the last 

 sensor and the anchor with a release mechanism 

 below the last sensor. The release mechanism is 

 a clock operated electrical firing squib that will 

 release the anchor on a short stay of line and 

 allow the buoy system to come to the surface. In 

 the present system the subsurface buoy has approxi- 

 mately 500 pounds of positive buoyancy and the 

 anchor weighs about 1,800 pounds. 



The most difficult problem encountered in this 

 mooring system is the slack painter. Fig. 1 

 shows the configuration selected after the sur- 

 face buoy line parted after being subjected to 

 a state 2 sea for approximately 2 hours. It is 

 necessary to have an electrical swivel at the top 

 of the subsurface buoy and a small submerged buoy 



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