Calibrating Inverted Echo Sounders Equipped with Pressure Sensors

Abstract

The addition of an accurate pressure sensor to the inverted echo sounder (IES) has allowed for the development of a new method for calibrating the IES's acoustic travel-time record without the need for coincident conductivitytemperature-depth (CTD) or expendable bathythermograph profiles. Using this method, the round-trip traveltime measurement of the IES can be calibrated into various dynamic quantities with better accuracy than was possible with previous methods. For a set of four IES records from the Newfoundland Basin, the estimate of the accuracy of the geopotential height anomaly (integrated between 100 and 4000 db) calibrated from the IES measurements was reduced from 0.65 to 0.52 m 2 s Ϫ2 , which is a substantial reduction toward the intrinsic scatter of the geopotential height anomaly versus travel-time relationship for this region (0.42 m 2 s Ϫ2). The addition of the pressure sensor to the IES results in reduced errors and eliminates the need for coincident CTD measurements. Moreover, the pressure sensor provides a complementary dataset recording the changes of the barotropic pressure field.

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

“…For this study, CTD sections from July 2010, December 2010, July 2011, and December 2012 are averaged in a fairly simple manner solely to provide an overview of the major water masses. The CTDs collected right at the PIES sites were also used to calibrate the PIES-measured travel times into the corresponding travel times that would be observed on a common pressure level (e.g., Meinen and Watts, 1998). …”

Spatial and temporal structure of the Denmark Strait Overflow revealed by acoustic observations

“…Integrating geostrophic measurements can be obtained with a PIES (Meinen and Watts 1998). It measures bottomto-surface acoustic travel time and bottom pressure with high precision.…”

Computation of Geostrophic Streamfunction, Its Derivatives, and Error Estimates from an Array of CPIES in Drake Passage

“…As described in Baker-Yeboah (2008) and Baker-Yeboah et al (2009), t is adjusted for (i) pathlength changes as determined by bottom pressure, (ii) the estimated inverted barometer effect of atmospheric pressure, (iii) the effect of latitude on gravity in converting between geometric height and pressure, and (iv) the seasonal cycle. It is then converted to travel time t index between the surface and an index level, here 2000 dbar, by fitting to t index 5 At 2 1 Bt 1 C, where coefficients A, B, and C are depth dependent and determined empirically from historical hydrography, with additional adjustments to C based on CTD profiles taken at each site during CPIES sampling (Meinen and Watts 1998;Baker-Yeboah 2008;Baker-Yeboah et al 2009;Donohue et al 2010). The depth chosen for the index level is a compromise between a level deep enough to capture most of the travel time variability and one shallow enough to retain a large number of historical hydrographic profiles extending at least to that level.…”