Figure 14 2 Sea Data tape recorder body right and COSMOS a 6 diameter pressure case Courtesy of W Hill circuit cards left The cards are rounded in order to fit into commercial cassette tape recorders are also available now for oceanographic use The second thread of engineering design mentioned above is platform engineering Since a review has recently been given by Henri Berteaux in his book Buoy Engineering 1975 we need not discuss this aspect in detail here Some aspects of platform engineering are included in the subsections on mooring technology in section 14 3 The reader interested in following current developments circa 1980 in ocean technology is urged to read Exposure a newsletter produced by R Mesecar of Oregon State University for discussion of new contributions and problems in instrument design and use in the ocean 14 3 Examples of Modern Ocean Instruments Looking over the period since The Oceans was written we can identify four major areas of instrument design that have had an important impact on the development of our ideas of ocean circulation and mixing These areas are the moored buoy current meter technology the deep drifting neutrally buoyant floats the temperature salinity profilers commonly known as the STD and CTD and the velocity profilers The first three of these developed essentially simultaneously The velocity profilers are newer and to some extent having built on the technology developed earlier have not yet had the total impact of the other three groups A second set of instruments proposed Our final discussion in this section covers a set of problems that can not yet be attacked with present technology New instruments are crucial for understanding and quantitative measurement Examples are air sea fluxes in stormy conditions or measurements in strong currents Space does not allow me to be comprehensive in any way here but only selective The reader is referred to two excellent recent review volumes Instruments and Methods in Air Sea Interaction NATOScienceCommittee 1978 and the Proceedings of a Working Conference on Current Measurements Woodward 402 D James Baker Jr II is in a state of devel opment and has not yet had the extended use or the impact of the four listed above These include for example bottom pressure gauges surface drifters and the inverted echo sounder We also include in this set the whole suite of remote measurements e g satellite altimetry and laser profiling of the upper layers and the various acoustic techniques that have been Mooers and Jensen 1978 which cover aspects of many of the instruments to be discussed below The paper by Rossby 1979 on The Impact of Technology on Oceanography contains a number of instructive examples Another area of very great impact on ocean measurements is navigation Advances in both shore based LORAN and satellite based navigation techniques are responsible for the success of many of the instrumental techniques discussed below from mooring location to velocity determination The discussion below is limited for reasons of space to instruments themselves In thinking about instruments and what they measure we consider the full equations of motion The equations include the terms to be measured ideally direct measurement of the terms is best but sometimes it turns out to be more feasible to measure the term indirectly The terms that appear in the equations involve the velocity products of velocity density pressure turbulent stresses and viscosity The instruments that we discuss for velocity include those that make direct measurements of currents either at a point or in profile We have been less successful in measuring turbulent stresses products of velocity fluctuations than the meteorologists primarily because of the lack of a stable platform However some useful data have been taken from stations on sea ice and are discussed below Density is generally inferred from temperature and salinity technical difficulties have precluded any useful instrument for measuring density directly The main problem is finding an instrument that will work in situ in the water column or on board ship The small variations of density and the large accelerations at sea have prevented much success with direct density measurement A number of techniques have been developed however and some of these will be discussed Pressure is generally inferred from the density using the hydrostatic relation Without some level of pressure reference however it is not possible to establish an absolute pressure field in the ocean Bottom pressure measurements to be discussed below in section 14 3 5 can monitor pressure fluctuations sea surface topography by satellite is a technique currently being developed for measurements of both fluctuations and mean surface field 14 3 1 Current Meter and Mooring Technology There are two parts to the measurement of currents at a point in the ocean The current meter must be accurate reliable and for most purposes internally recording The platform or mooring must be robust deployable and affordable Major advances in both of these areas have been made since the 1960s It is now possible to make long term greater than 1 year measurements of currents at levels below the surface layer with better than 90 data return e g Pillsbury Bottero and Still 1977 Tarbell Spencer and Payne 1978 The paper of Richardson Stimson and Wilkins 1963 is a good starting point because it marks the beginning of the modern age of current meter and mooring technology This remarkable paper covers the whole field of mooring and current meter technology as it was known at that time and demonstrates the ingenuity of W S Richardson and coworkers then at the Woods Hole Oceanographic Institution The paper documents the early attempts to maintain deep sea moorings and current meters along a section from Woods Hole to Bermuda across the Gulf Stream For this purpose they needed a new current meter that would record for a long time and a sturdy reliable mooring for a platform Richardson et al were influenced by Swallow s measurements 1955 1957 with neutrally buoyant floats which revealed a variability in the measured currents large compared to the residual drift They argued that in deep water where large variability is encountered the significance of short term measurements is in serious doubt They noted that the float tracking could be extended to longer times but that as the required measurement time increases equipment that may be left at sea unattended becomes
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