ASA 127th Meeting M.I.T. 1994 June 6-10

2aUW4. Ocean variability, modal group delays, and the detection of climate signals with vertical arrays.

Arthur B. Baggeroer

Depts. of Ocean and Electrical Eng., MIT, Cambridge, MA 02139

The monitoring of ocean variability and climate using global acoustics depends upon detecting travel time changes of the resolvable modes and/or raypaths. An analysis based upon the modal group delays is considered. It is assumed that they contain the information that acoustic probes can yield about an adiabatic ocean; consequently, a water column-spanning vertical line array that measures all group delays can extract all the information about ocean variability and climate that acoustics can provide. The vertical slice is modeled along the path with two components: (i) a set of possible climate signals, e.g., warming at the surface or at the SOFAR duct and (ii) a natural variability based upon the ocean dynamical modes. Noise is included in the measurements of the delays due to acoustic signal-to-noise ratios, finite bandwidths, and array imperfections. Then the covariance of the modal group delays due to natural variability is found and estimation theory bounds are evaluated on how well the climate signals can be estimated using vertical line arrays to measure the group delays. [Work supported by ARPA.]