The use of invariants for detecting weak signals in the near acoustic illumination zone

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In solving many practically important problems of hydroacoustics, the properties of the fan interference structure of the signal intensity field are used, which in the shallow sea in the coordinates “distance – frequency” are largely determined by the value of the waveguide invariant β (S.D. Chuprov invariant) close to one. Below, the properties of the waveguide invariant are studied in the near acoustic illumination zone (NAIZ) of the deep sea, and it is found that its values are unstable – when the propagation conditions change, the waveguide invariant varies widely and is not an invariant. It is shown that in the NAIZ the use of the phase-energy invariant βef is more promising, since in the NAIZ it is equal to one with high accuracy and stable. It is also discovered for the first time that, under certain conditions, coherent addition of Fourier components on the complex plane is possible in the NAIZ if, when summing the spectral components of complex spectra along the ridges, an adjustment for phase variation is introduced. With such processing, in the case of stationary noise, the probability of detecting weak signals can significantly increase.

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作者简介

S. Aksenov

Prokhorov General Physics Institute of the Russian Academy of Sciences

Email: skbmortex@mail.ru
俄罗斯联邦, Moscow

G. Kuznetsov

Prokhorov General Physics Institute of the Russian Academy of Sciences

编辑信件的主要联系方式.
Email: skbmortex@mail.ru
俄罗斯联邦, Moscow

参考

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  3. Kuznetsov G.N., Kuz’kin V.M., Pereselkov S.A. Estimation of the velocity of underwater objects in the passive mode using frequency-shift data // Phys. Wave Phenom. 2014. V. 22. № 4. P. 306–311.
  4. Zhu Q. et al. The waveguide invariant close to the deep-water bottom // Applied acoustics. 2024. V. 217. P. 109870.
  5. Emmetiere R. et al. Understanding deep-water striation patterns and predicting the waveguide invariant as a distribution depending on range and depth // JASA. 2018. V. 143. P. 3444.
  6. Аксенов С.П., Кузнецов Г.Н. Энергетические инварианты в звуковых полях глубокого и мелкого моря // ДАН. 2022. Т. 507. № 1. С. 9–14.

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2. Fig. 1. VRSZ in a selected area of ​​the Norwegian Sea, August (long-term average data).

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3. Fig. 2. Spatial distribution of |P(f, r, zs, z)|2 in the BZAO in the mode WKB approximation: f = 300–700 Hz, zs = 100 m, z = 150 m, r = 0.01–2.0 km; light lines – 13 ridges f3(r)–f15(r).

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4. Fig. 3. Acoustic intensity (a) in the BZAO in the mode WKB approximation; phase-energy invariant βef (b), f = 300–700 Hz, zs = 150 m, z = 20 m, r = 0.01–2.0 km.

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5. Fig. 4. Dependences of the sound pressure amplitude and grazing angles on the distance. 1 – sound pressure amplitude in the mode WKB approximation, 2 – sound pressure amplitude in the ray approximation, 3 – grazing angle of the “direct” ray at the reception point, 4 – grazing angle of the ray reflected from the free surface at the reception point, 5 – βef . 50 at zs = 150 m, z = 20 m, r = 0.01–1.7 km and two frequencies: f = 50 Hz (a); f = 300 Hz (b).

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6. Fig. 5. 1 – amplitude along the ridge with number n = 1 in the ray approximation, 2 – phase increment along the ridge with number n = 1, 3 – β . 100 along the ridge with number n = 1 at zs = 150 m, z = 100 m, r = 0.01–2.6 km, f = 3.7–443 Hz.

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7. Fig. 6. 1 – phase increment along ridge number 2 (see Fig. 3) in the ray approximation, 2 – the same in the mode WKB approximation (curves 1 and 2 are not distinguishable); 3 – amplitude along the ridge of the interferogram with number 2 in the ray approximation; 4 – the same in the mode WKB approximation: r = 690–1165 m, f = 302–695 Hz, zs = 20 m, z = 150 m.

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8. Fig. 7. 1 – phase increment along the ridge number 2 (see Fig. 3); 2 – amplitude along the ridge; 3 – incoherent sum along the ridge, 4 – coherent sum along the ridge: r = 687–1169 m, ∆r = 0.1 m, f = 300–700 Hz, zs = 20 m, z = 150 m.

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