The Processing and Application of Inverted Echo Sounder Data from Drake Passage

Abstract

Bottom pressure recorders (BPRs) have been deployed at Drake Passage (DP) to monitor changes in the volume transport of the Antarctic Circumpolar Current (ACC) through the passage. The use of inverted echo sounders (IESs) in assisting the interpretation of the BPR data is presented. The initial data processing of the IES data is outlined, and the accuracy of the data described. The most significant limitation on the application of the data is the presence of a sea-state bias with a root-mean-square value of around 0.4 ms. IES data are shown to perform well at determining whether individual changes in bottom pressure are due to changes in cross-passage-averaged barotropic transport or due to the effect of meanders, eddies, and/or lateral shifts of ACC fronts. The conversion of acoustic travel time to more useful oceanographic parameters (dynamic height, baroclinic pressure, inverse-barometer-corrected sea level) is described. A method for improving the performance of very deep bottom pressure in monitoring ACC barotropic transport changes is described for the case where the BPR?IES instrumentation is deployed near an ACC front. Reasons for the inability of this method to improve the ability of shallower pressure records in monitoring the ACC are discussed, and suggestions for future refinements are outlined.