Tomographic resolution of mesoscale eddies in the marginal ice zone: A preliminary study

Abstract

The adequacy of ocean acoustic tomography to resolve mesoscale eddies in the marginal ice zones (MIZ) in the vertical plane containing the acoustic multipaths connecting a pair of transceivers is studied using simulation inversions based on realistic eddy profiles obtained from conductivity‐temperature‐depth data. Resolution in this plane is seen to be strongly dependent upon the characteristics of the sound channel. For optimal, minimum mean square error estimators, resolution is directly related to accuracy, with better resolution implying higher accuracy. For unaided acoustic tomography (i.e., no supplementary measurements) using only non‐bottom‐interacting paths, horizontal and vertical resolution lengths of the order of 40 km and 200 m, respectively, are found in the upper water column for a transmission range of 150 km. The implication is that the horizontal resolution is marginally adequate to resolve MIZ eddies but the vertical resolution is not, since the horizontal scale of the eddies is of the same order whereas the vertical scale is much shorter. The incorporation of bottom‐reflected arrivals is found to improve resolution significantly. However, the improvement only occurs in the horizontal direction and saturates when more than 14 of these arrivals are included. Beyond this point, additional travel time observations give mostly redundant information. On the other hand, the disappearance of less stable non‐bottom‐interacting ray paths can result in a significant loss of resolution, but only vertically. The deficiency in vertical resolution is a result of the upward refracting nature of the MIZ sound channel. It is also demonstrated that the inclusion of point temperature measurements on the acoustic transceiver moorings can dramatically increase the vertical resolution of the overall system, particularly within a horizontal correlation length of the mooring. With the inclusion of satellite radiometry surface temperature measurements, adequate vertical resolution is achieved over the entire range considered.