Application of empirical orthogonal functions for estimating the influenceof biological characteristics on the synoptic variability of the strength of sound volume backscattering in the Tropical Atlantic

We studied the possibility of classifying the vertical profiles of the stre ngth of sound volume back-scattering (SVBS) in the upper productive layer o f the Tropical Atlantic, when decomposed into empirical orthogonal function s (EOF), and of determining the influence of the biological processes of va rious scales on the stratification of the SVBS strength. An analysis of the data from 228 stations indicates that, in the eastern and western parts of the entire study area, the SVBS strength field is characterized with an ac curacy of 95% by different numbers of EOF The eastern part of the study are a, which is distinguished for its higher biological productivity and greate r dynamics of the water masses, has a dominating effect on the dispersion o f the SVBS strength. The 95% accuracy of the approximation of the dispersio n of the SVBS strength field at daytime is reached in the eastern part of t he study area by a sum of only five lower modes, while in the western part, the required number of them is nine. At nighttime, this relation is somewh at equalized (six and seven), while the dominating contribution of the east ern part of the study area is conserved. The result of the operative analys is of the hydroacoustic characteristics at frequencies of the order of 80 k Hz can be used for the classification (typification) of the water masses wi th regard to their biological productivity.