17 February, 1998
Today I was asked to do some XBTs. (Expendable Bathy Thermographs). Brian Williams, our Electronics Technician, explained that they were developed by the Navy to track submarines in World War II. Sonar will bounce off of a thermal inversion (warm water layer trapped under cold water layer). Enemy submarines would take advantage of that fact and hide under a thermal inversion. XBTs would be deployed periodically to determine if a thermal inversion were present, thus increasing the likelihood that an enemy submarine might also be lurking below.
The XBT is supported by software in the Electronics Lab. The device that launches the probe looks something like a caulk gun with a large cable that's connected to the boat wiring coming from the back of it. The probe itself is housed in a two inch diameter black tube and looks like a large rifle cartridge. The probe in its housing is loaded into the launch device and locked into place. The locking triggers the software to display that it is ready to launch the probe. Carefully extending the launching device over the port stern (left back) rail, I carefully deployed the device by pulling the locking pin and ..... merely tipping the housing so that the probe fell into the water. (Hah! You thought there would at least be an explosion to send the probe off! So did I, but a mere plop in the water was all the sound with which I was rewarded.) A very thin copper coil linking the probe to the computer, relaying back the temperature information desired, played out until there was no more wire. At that point I merely pulled the wire in two and the probe fell to whatever depths there were at that moment.
I can see Tierra del Fuego in the distance already. Within two hours we will be out of the Drake Passage with no sign of its fierce reputation on this passage either. That is one experience of Antarctica that I was happy to forego.
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