HMAS COOK VKMS - 94104 Mk9 XBT System

16/02/1990 - 11/03/1990

Many traces from this cruise have an error in the hit bottom depth. The
hit bottom depth is lower than the charted depth.  This is due to a
timing error in recognition of the start of descent of the XBT probe.

This error has been documented by the CSIRO in "Quality Control
Cookbook for XBT Data, CSIRO Marine Laboratories Report No. 221, 1994"
in Section 2.8 as a 'Sippican Mk-9 Timing Delay Problem or Driver Error'.

The error is most obvious in shallow water areas less than 
80m and is intermittent. The error varies between approx.
5m to 25m.

For example see trace no. 59 which has a hit bottom depth
of approx. 15m whereas the operator entered charted depth
is 33m.

This error also been noted by Les Hamilton of DSTO who deployed
Mechanical Bathermographs on this cruise at the same time as the XBT's.
Hamilton noted a depth error between the MBT sensed depth and XBT depth
varying from 5m to 26m. On some occasions there is little or no error
indicating the intermittant nature of the problem.

Drops 178 - 188 have confirmed inversions.

Drops 194-195 have inversions
196 to 199 speed 25.65 knots but positions okay

201-202 inversions in NE Indian Ocean.