Abstract:

Sonobuoy measurements of merchant ships were processed for mean levels and fluctuation dynamics of the broadband and line components from a large database of ships. Direct path results are reported. The mean levels are compared with various ship source level models. The levels are shown to agree with Ross-type models with some minor differences noted. The importance of source characterization, particularily source depth, in interpreting these results is emphasized. Fluctuations of the broadband component are shown to vary by as much as 6 dB with periods of 10--20 s for a limited number of ships. The results are shown to be consistent with the hypothesis that they are due to ship motion in the water. Examples are provided of ship line temporal variation in frequency and amplitude. Preliminary work on categorizing the data according to the spectra characteristics and time behavior is discussed.