Sound extinction by fish schools: Forward scattering theory and data analysis

Abstract

A model used previously to study collective back scattering from fish schools [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196-208 (1996)], is used to analyze the forward scattering properties of these objects. There is an essential physical difference between back and forward scattering from fish schools. Strong frequency dependent interference effects, which affect the back scattered field amplitude, are absent in the forward scattering case. This is critically important for data analysis. There is interest in using back scattering and transmission data from fish schools to study their size, the species and abundance of fish, and fish behavior. Transmission data can be processed to determine the extinction of the field by a school. The extinction of sound depends on the forward scattering characteristics of the school, and data inversion to provide information about the fish should be based upon a forward scattering paradigm. Results are presented of an analysis of transmission data obtained in September 1995 during an experiment performed in the Gulf of Lion in the Mediterranean Sea [Diachok, J. Acoust. Soc. Am. 105(4), 2107-2128 (1999)]. The analysis shows that using forward scattering leads to significantly larger estimates of fish abundance than previous analysis based upon back scattering approaches.

In Situ Measurement of Sound Attenuation by Fish Schools (Japanese Horse Mackerel, Trachurus japonicus) at Mid-Frequency Bands

“…However, the attenuation by the fish schools is related not only to the size but also to the volume density. The fish school density per volume is generally about 145 ind./m 3 when calculating the void fraction (β = (4/3)πr 3 ) [21,30], and about 126 ind./m 3 based on the theoretical aggregative packing model of fish school density (V f ish = 0.6SL 3 ) [31] of the mean standard length (SL) of horse mackerel in this experiment. The previous study was compared intensively with the Exp3 results of about 100 ind./m 3 in this study (Figure 2b).…”

“…Diachok (2005) conducted a study on estimating the number density from the attenuation of anchovy schools during the day and night at the mid-frequency range of 1-3 kHz in shallow water environments through transmission loss measurements [20]. Raveau and Feuillade (2015) recently studied sound extinction by fish schools on the basis of the forward scattering theory [21]. However, these previous studies mainly focused on attenuation by individuals or schools of fish at high-frequency bands.…”

Resonance distribution in the quantum random Lorentz gas

“…Among the fundamental tools, a remarkable one is the multiple scattering method which consists in solving the self-consistent equations based on the free-space Green function. This method is commonly used in many fields of application including optics, underwater acoustics [1][2][3][4], and electronic band computations in solid state physics [5,6]. This method enjoys great freedom in the choice of the collisional and geometrical properties for the scatterers, such as their positions.…”