METHOD OF ESTIMATING THE NUMBER OF PROPELLER BLADES OF A NOISY OBJECT IN SEA Russian patent published in 2020 - IPC G01S3/80 

FIELD: hydro acoustics.

SUBSTANCE: invention relates to the field of hydro acoustics and can be used for recognition of sea vessels by their noise emission. In the proposed method, a noise signal of a moving ship is received by a combined pressure gradient receiver, digitizing, filtering, performing spectral analysis by FFT, generating spectra of total signal plus interference S+N process for a complete set of 16 informative parameters characterizing the sound field, generating interference spectra N for a complete set of 16 information parameters, forming the S/N signal-to-interference ratio for the complete set of 16 information parameters, selecting the discrete components in the comparator, which correspond to maximum values of S/N ratio of 16 possible, determine harmonic row of vane frequencies f_max(nz), n = 1, 2, 3, etc., which correspond to maximum values of ratio S/N at output of comparator, and minimum of them are taken as first blade frequency f_b(z), finding in the spectrum of the signal at the output of the comparator a minimum difference frequency f(nz)-f(nz-1), which is taken as the first rotational frequency f_r(1)=f(nz)-f(nz-1), n = 1, 2, 3, etc., estimated value of number of propeller blades is calculated by formula z₀(i)=f_b/f_r, generating a set of reference spectra S(i)=cos(2πfz(i)/f_max), where S(i) is the reference spectrum for the hypothesis of number of blades number i, containing a rotational-blade tone row characteristic of the number of propeller blades z(i), calculating for each S(i) its measure of similarity K(i) with the spectrum of the analyzed signal, plotting the function R(φ)=K(i)cos(φz₀(i)), φ=(0, 2π) for found approximate value of number of propeller blades z₀(i)=f_b/f_r and if resultant shape is similar to that of screw with z₀(i) blades, then it is concluded that the observed noisy object has a number of blades equal to z₀(i).

EFFECT: disclosed method enables to significantly increase interference immunity of the receiving antenna without increasing its aperture, but only by increasing the number of informative parameters, the maximum number of which is equal to 16, increase the signal-to-interference ratio at the output of the comparator, which selects for each current time point a spectral component with a maximum S/N ratio from set of 16 information parameters; in its turn, increased number of informative parameters allows to increase probability of correct detection of the first blade frequency and the first rotational frequency and thus probability of correct estimation of quantity of vane blades, which is classification feature of the noisy object itself.

1 cl, 4 dwg