- 6 - 
The XBT probe contains a thermistor in its nose (Fig. 4). The 
electrical connection between the probe and the SEAS control 
ler is made when the canister containing the probe is placed 
within the launcher. While the ship is underway, the observer 
drops the probe by pulling the retaining pin. The thin two 
conductor signal wire dereels from the probe as it descends 
vertically through the water and, simultaneously, wire 
dereels from the spool within the canister, thus compensating 
the ship's movement. The XBT system uses seawater ground 
and, after water impact, the circuit is complete and 
temperatures - in terms of thermistor resistances - are 
telemetered to the shipboard system. The controller samples 
the data with 10 Hz and converts the resistance to voltage. 
The voltage versus time information is transmitted in real 
time to the computer which generates a real-time plot of 
ocean temperature versus depth on the screen. 
Data acquisiton ends when the XBT probe exceeds maximum 
depth depending upon the ship's speed (Fig. 5), and the wire 
breaks, or the operator terminates the data cycle. Then the 
data are saved automatically on a cartridge tape for later 
scientific analysis. 
Optionally, as a next step - and for operational purposes 
only - significant points of the temperature profile (in 
flection points) are calculated by searching for changes in 
vertical gradients of temperature (Fig. 6). 
Fig. 5: 
The maximum depth as a function of ship's speed 
(after Sippican Ocean Systems, Inc.)