IES Calibration for Main Thermocline Depth: A Method Using Integrated XBT Temperature Profiles.

Abstract : A new method of calibrating Inverted Echo Sounder (IES) travel time measurements to main thermoclinedepths is described. Unlike the traditional method in which the thermoclineis defined by a point measurement, such as the depth of the 12 deg C isotherm depth as measured with an XBT, this technique utilizes the full temperature profile of XBT casts. The advantage of this method is that the vertical integralof temperature, QT= Tdz is conceptually and empirically very closely correlated with the acoustic travel time measured by the IES, r=2 c-1 dz. Comparisons of the new method with the more traditional point method show that the root-mean-square error in the calibration (11 m standard deviation) is 1/3 as large as before, and outlier values are significantly reduced. The final coefficients used to calibrate the SYNOPCentral and Inlet Array IESs are tabulated.