study of a specific area in a short time. A good example of re- 

 sults of a concentrated effort is the NORPAC Atlas (1955). ^ The 

 North Pacific Expedition represented a concerted effort of Japan 

 and the U.S. , involving 19 research vessels and 1002 hydrographic 

 stations. Most of the data were taken within one month, showing 

 the intensity of the effort. Coastal stations were about 30 miles 

 apart and oceanic stations were from 50 to 120 miles apart. The 

 distance between hydrographic stations is the determining factor 

 in computing horizontal gradients. Horizontal-temperature 

 gradients derived from such sets of data are termed "average 

 gradients" and represent the average temperature change per 

 nautical mile for a given depth. 



Average horizontal-temperature gradients may also be 

 determined from two or more space- separated bathythermograph 

 stations. During underwater acoustic experiments, it is not 

 uncommon to determine the average gradient from the difference 

 of two bathythermograph readings — one taken at the transmitting 

 ship, the other at the receiving ship. 



Minute physical features, the temperature in particular, 

 have not been investigated as widely as large-scale features 

 even though horizontal thermal microstructure was observed 

 during World War II when Holter (1944) made measurements from 

 a submerged submarine using a thermopile. 2 He detected 0.02°F 

 differences over horizontal distances of about 30 feet. Other 

 contributors in this area include Urick (1948) who, near Key West, 

 detected gradients similar to those found by Holter and concluded 

 also that gradient increased with depth within the mixed layers. 3 

 From experimental work in deep water, Sheehy (1950) concluded 

 that acoustic intensity fluctuations were caused by inhomogeneities 

 in the water. 4 Lieberman (1951) detected inhomogeneities of 

 mean size of about two feet (60 cm) and temperature variations of 

 0.05° Celsius (C) . 5 Using Lieberman's results, Mintzer (1953 

 and 1954) made theoretical predictions of intensity fluctuations 

 produced by temperature microstructure in the sea. 6 Priimak 

 (1961) carried out a statistical analysis during a three-dimensional 

 study of the sea, with investigations of the parameters and statis- 

 tical characteristics of the fluctuations in temperature and 



1. Superscript numbers denote references in list at end of this report. 



