ASA 125th Meeting Ottawa 1993 May

4aUW3. Holographic array processing using truncated arrays.

Azmi A. Al-Kurd

Robert P. Porter

Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105

Imperfect knowledge of the salient characteristics of the propagation medium limits the performance of acoustic array processors at long ranges in the ocean. Holographic and phase conjugation techniques can be used to diminish the range integrated effect of the medium and reconstruct the wave front in the vicinity of a scatterer or other signal source. Then, using a backpropagation technique, which focuses sound at the position of the unknown source, the location of the source can be determined. In deep water, the idealistic situation of having a receiving array and reference source that span the water column is prohibitively complex. In this paper the effect of truncating both the receiving and virtual arrays on the performance of the holographic array processing algorithm is presented. The analysis was carried out using normal mode theory, and the simulation for a range-dependent ocean was performed using a wide angle PE (parabolic equation) code, FEPE. It is shown that the holographic array processing algorithm is more sensitive to the length of the virtual array than to the length of the receiving array.