bias due to ambiguity, are set by the instruments and techniques of measurement. The kind of residual 

 ambiguity which can be tolerated, that is the criterion of goodness of an ambient noise directionality 

 measurement, must be related to eind partly determined by the use. The choice of criterion of goodness 

 sensitively affects both measurement and analysis methods. A simple corollary is that there is no way to 

 measure ambient noise directionality which is best for all applications. 



The variety of criteria of goodness which have already been used shows that there is no obvious 

 unique best choice. Unfortunately, some of the sources cited in this paper fail to state and all fail to 

 justify their choices of goodness criteria, even for the particular applications they have in mind. It 

 should not be inferred that their selections are poor or irrelevant, for responsible and experienced 

 scientists and engineers can be counted on to do most things right even when they do not defend each 

 decision explicitly. However, their lack of comment on their choices of criteria makes it difficult to 

 compare them or to decide which among them is most suitable for a particular application. 



The validity of the assumptions which make any of the severed error optimizations realizable is 

 doubtful and would be extremely hard to verify. A direct comparison among the methods, using real 

 data, is probably the best approach to try next. Reference 5 shows the way to make such comparisons, 

 but does not go far enough, for it does not objectively match the merits and deficiencies of each method 

 to the requirements of the applications. 



ACKNOWLEDGMENT 



My remarks are stimulated mostly by experience with the LRAPP-sponsored EASTLANT II exercise 

 (Refs. 1, 2, 6, 7, and 8) and SQUARE DEAL Exercise (Refs. 9 and 10). This has involved me intimately 

 with IT ASS (Refs. 1, 6, and 7), less initimately with a long seismic array originally developed for geo- 

 physical exploration (Refs. 2, 9, and 10), and to a lesser extent with an experimental directional towed 

 array, STELLA (Refs. 9 and 10), developed in the United Kingdom. I must also acknowledge a debt to 

 Messrs. Pastore, Elyash, and Nuttall at NUSC, Messrs. Wagstaff and Gardner at NUC, Messrs. Gill and 

 Wilson at ARL in Teddington, England, Mr. Sullivan at ADL, and many others whose verbal and written 

 communications I have profited from. 



Most of this work was carried out under contract NOOO-14-72-C-0173 with the Office of Naval 

 Research under the Technical Monitorship of Dr. Roy Gaul, Manager, LRAPP, whose guidance is 

 acknowledged with thanks. 



^ EASTLANT II Acoustics Exercise Plan MC Plan 07, Long Range Acoustic Propagation Project (July 1972) 



^ SQUARE DEAL Exercise Plan, MC Plan 012 Long Range Acoustic Propagation Project (1973) 



^"D. Sullivan, G. E. Miller, and G. Raisbeck, SQUARE DEAL Synopsis Report MC Report 0015, Long Range Acoustic 



Propagation Project, (Feb. 1974) 



90 3 



* U. S. GOVERNMENT PRINTING OFFICE : 1977 O - 244-457 



