The use of receiving arrays for measuring underwater noise levels of moving sources

Near-field measurement of radiation levels of extended spatially uncorrelated sound sources

“…As can be seen, noise sup pression takes place in the entire range of angles; how ever, in the angular sector corresponding to region Ω observed from the center of the AA, the error sharply † ; w w † 0 ( ) ( ). increases due to nonrobustness of the solution for noise covariance matrix (11). Physically, the appear ance of nonrobustness is related to the contradiction that arises during minimization of (10).…”

“…Using in (10), instead of (11), identity matrix I, this effect is naturally elimi nated, but the gain in interference immunity is thereby also lost (see the dotted curves in figure 2). It is possi ble to achieve a reasonable compromise by adding to the right hand side of (10) the summand which corresponds to the known approach (the so called diagonal loading) representing an increase of the main diagonal of the empirical estimate of the noise covari ance matrix in adaptive AAs [10]; this approach was also successfully used in [11]. Functional Φ(w, α) thereby passes to (12) where α, β ≥ 0 represents two parameters.…”

“…EXPERIMENTAL RESULTS Below we present the results of experimental test ing of the method on data obtained under shallow sea conditions [11] when using a vertically deployed 11 element receiver AA with a length of 30 m. The underwater noise of a ship passing over the AA played the role of the source whose emission was used to test the quality of synthesizing the spatial selectivity char acteristic (SSC) . As the Green's function, we used function G 1 , which describes sound propagation from a z dipole.…”

“…The requirement of a minimum of the product of the norm of the WV and the noise level at the AA output is physically obvious. A nearly equivalent criterion, proposed and used in [11], is to determine β from the condition…”

Reconstruction of the time dependence and signal parameters of far-field extended wideband sources: Part 1. Reconstruction techniques and technical instruments

“…Using the accepted hypothesis about the equiprob able arrangement of single sources at aperture L, we find the transfer function and its spectrum as the averages over the transfer func tions constructed for the total set of points x i located at aperture L: (13) Here is the transfer function at which an array output signal and a far zone signal from a local source located at point x i are related by (6). Another defini tion of is the complex amplitude of an array output signal, which is caused by unitary (per 1 m) waves from a tone source located at the point x i .…”