EFFECTS OF MODAL PHASE ERRORS ON EIGENVECTOR AND NONLINEAR METHODS FOR SOURCE LOCALIZATION IN MATCHED-FIELD PROCESSING

Modal phase errors due to rough surface scattering can perturb the algebraic structure of the cross spectral matrix, on which the success of eigenvector and nonlinear methods of source localization depends. By examining the perturbed structure one can determine what source information can be obtained from ambiguity surfaces and what information must be extracted by other means. For significant levels of phase error some type of preprocessing to suppress some sources in favor of others may be necessary, for example, the "sector-focusing" of Byrne and Steele. What information can be obtained from ambiguity surfaces depends on the array geometry. For vertical arrays source range and depth can be determined from the ambiguity surface if there are no modal phase errors, but when phase errors are present other methods may need to be employed. For horizontal arrays bearing, range, and depth of (nonbroadside) sources can be determined from ambiguity surfaces in the case of no modal phase errors; however, if modal phase errors are present it may not be possible to determine anything about the sources from the ambiguity surface.