James H. Wilson
Dept. of Oceanogr., Naval Post Graduate School, Monterey, CA 93943
The recent at-sea, real-time signal detection and tracking performance of the plane-wave solution to the inverse beam forming (IBF) integral equation (Wilson, 1983; Nuttall and Wilson, 1990) has shown significant (5 to 12 dB) gains compared to operational sonar systems and other adaptive processing methods. The Fourier integral method (FIM) (Nuttall and Wilson, 1990) was thought to be the ``spikiest'' solution to the IBF integral equation, that is also linear in the covariance matrix. A standard inverse technique (Backus and Gilbert, 1968) used in tomography has recently been applied to the IBF integral equation, and two new theoretical results have been obtained. First, the plane-wave solution, called the least-squares Wilson integral method (LSWIM), agrees with FIM only at the array design frequency, and is spikier or more ``delta function like'' than FIM below array design frequency. Second, the non-plane-wave or matched-field solution was obtained by allowing the measured data vector (covariance matrix) in the Backus--Gilbert inverse method to have two discrete indices instead of the usual one index. This work was performed during the analysis of Outpost SUNRISE data for the purpose of enhancing sonar detection and tracking performance, but has also a more general application in acoustical oceanography. [Work supported by AEAS.] [sup a)]On temporary leave from Neptune Sciences, Inc.