Bathythermograph

[2] While the instrument is being dropped, the wire is payed out until it reaches a predetermined depth, then a brake is applied and the BT is drawn back to the surface.

According to watchstander Edward S. Barr: "… In any kind of rough weather, this BT position was frequently subject to waves making a clean sweep of the deck.

It was not at all uncommon, from the protective position of the laboratory door, to look back and see your watchmate at the BT winch completely disappear from sight as a wave would come crashing over the side.

"[6] After witnessing firsthand the dangers of deploying and retrieving BTs, James M. Snodgrass began developing the expendable bathythermograph (XBT).

I have in mind a package which could be jettisoned, either by the "Armstrong" method, or some simple mechanical device, which would at all times be connected to the surface vessel.

However, it would unwind as it goes a very fine thread of probably neutrally buoyant conductor terminating at the float unit, thence connected to the wire leading to the ship.

The fall rate equation takes the form: where, z(t) is the depth of the XBT in meters; t is time; and a & b are coefficients determined using theoretical and empirical methods.

From that the 2008 NOAA XBT Fall Rate Workshop[11] began to address the problem, with no viable conclusion as to how to proceed with adjusting the measurements.

In 2010 the second XBT Fall Rate Workshop was held in Hamburg, Germany to continue discussing the problem and forge a way forward.

The introduction of Argo floats has provided a much more reliable source of temperature profiles than XBTs, however the XBT record remains important for estimating decadal trends and variability and hence much effort has been put into resolving these systematic biases.