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- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 definition "Vertical profiles of salinity and temperature in the ocean have been obtained by a variety of instruments, referred to here generically as STDs or (when the salinity is obtained by way of the water's conductivity) CTDs. Data described in the Master Directory have in some cases been obtained over considerable periods of time and by a variety of investigators. Hence, the specifics of the STDs vary considerably - sometimes within the same data set. For descriptions of the instrumental sources and characteristics of a particular data set, investigators will have to contact the appropriate archive. The brief sketch of salinity, STDs and CTDs given below is taken from a standard and well- accepted text in descriptive physical oceanography. It is intended for those not already familiar with the field. Temperature and depth are physical parameters common to all science - indeed common to ordinary language; salinity is much more specialized. The total amount of dissolved material in sea-water is termed the 'salinity' and is defined as 'the total amount of solid materials in grams contained in one kilogram of sea-water when all the carbonate has been converted to oxide, the bromine and iodine replaced by chlorine and all organic matter completely oxidized'. For example, the average salinity of ocean water is about 35 gm/km of sea water, usually stated as 'thirty-five parts per thousand'. One of the more remarkable features of sea-water is that while the total concentration of dissolved salts varies from place to place, the ratios of the more abundant components remain almost constant. The direct determination of salinity by evaporating sea-water to dryness is too difficult to carry out as a routine process. Instead, the classical (Knudsen) method of measurement exploits the observed invariance of component ratios. One first determines the chlorinity by titration with standard silver nitrate solution and then scales up to the salinity by a relation based on the measured ratio of chloride ion to total dissolved substances: Salinity = 1.80655 X Chlorinity In routine use, an accuracy of 0.02 parts per thousand is considered reasonable for this laboratory technique. More advanced lab procedures easily yield accuracies of 0.003 parts per thousand. In the 1960s inductive salinometers were developed for in situ use and a number of such instruments are now available. Because they measure Conductivity, Temperature and Dept, they are generally referred to as CTD instruments. Accuracies of 0.005 parts per thousand, 0.005 degrees C and 0.15% of full scale depth are claimed (Pickard, p.93). The table below (from the CRC Handbook of Marine Science, p.550) gives more modest values for several commercially available in situ instruments. MANUFACTURER SALINITY TEMPERATURE DEPTH parts per degrees C* meters* thousand* Beckman RS6 0-40 (0.2) 0-30 (0.2) 0-130 (2.5) Geodyne 30-40 (0.02) -2-35 (0.05) 0-9000 (0.25%) Kjeler 30-40 (0.3) -2-35 (0.02) 0-2500 T.S.K. 29-36 (0.03) -2-32 (0.2) 0-100 (3%) * Accuracies are given in parentheses, in the appropriate units unless percent is indicated. _________________________________________________________________ Taken from: Pickard, G.L, Descriptive Physical Oceanography, 3rd edition, Pergamon Press, Oxford, 1979. ISBN 0-08-023824-6 Smith, F.G.W, (Editor), CRC Handbook of Marine Science, Volume I, CRC Press, Cleveland, 1974. ISBN 0-87819-388-X (Complete Set) Additional information available at 'http://www.aanderaa.com/SalTempDepth3230.htm'" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 id "1655714" @default.
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- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 path_id ff564c87-78f2-47eb-a857-a4bdc0a71ae5 @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 path_id ffa3a835-903a-462a-adfb-fc0d25ba07d0 @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 path_label "In Situ/Laboratory Instruments" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 path_label "Instruments" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 path_label "Profilers/Sounders" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 prefLabel "STD" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 reference "" @default.
- ea2626ec-fc8d-47b1-9bad-7d69ce23f7b2 tag "Instruments" @default.