Since the temperature change (i.e., signal) for a given ver- 
tical displacement* in the thermocline is proportional to the ver- 
tical temperature gradient, this region is a desirable one in which 
to operate. To measure the vertical displacement of isotherms in 
the thermocline, fairly close spacing of sensor elements, precisely 
located, is required. Close, precise spacing can be achieved with 
the moving strut internal wave recorder described here. The re- 
sults obtained in a successive determination of such vertical dis- 
placement of isotherms can be portrayed as a function of time (fig. 
13), the curves representing internal waves. 
APPARATUS 
A vertical array of temperature sensors was achieved by in- 
stalling a number of normalized thermistors, equally spaced, in 
the leading edge of a vertical strut. The strut was mounted at the 
bow of a submarine (see fig. 1A for a low drag strut, and fig. 1B 
for tower). The thermistors operated on linearizing bridges, the 
outputs of which were recorded sequentially. Once each sequence, 
the output of a pressure transducer (designed to determine the 
depth of the strut) was also recorded as indicated schematically in 
figure 2. 
THE STRUT 
The first strut used was wooden, and 18 feet in length. Its 
leading edge was semicircular, with radius of 3 inches. For ease 
of construction, the strut was faired with a straight-sided wedge 
such that the chord was 18 inches. At 6 knots, the coefficient of 
drag was estimated at 0.16, and thus the estimated total drag on 
the strut was 230 pounds at 6 knots. The foot of the strut was 
mounted in a steel boot, and the strut held in place by a number of 
*The vertical displacement as a function of depth is also probably a 
maximum at the thermocline for the type of problems the authors 
are interested in. 
