In the split beam (SB) echosounder, the sample range of target strength (TS) is limited due to the directional ambiguity of echo. This problem can be avoided to a large extent by transducer design which reduce side lobe level. We examined the sample range of TS in transducer steered arrays by introducing appropriate window function. It involves amplitude shading and form of array elements.
The target size is largely greater than the wavelength, the TS described by the model is proportional to the cross section area and independent of the frequency. For wild fish, TS would vary between individuals, and the average value would be less than the maximum recorded in dorsal aspect. Therefore it has variance length and aspect, we design the window function with 50dB sample range of TS. The SB method transducer divided four quadrants employed window function described by form and weight. The angle φ in the horizontal plane is determined from the electrical phase difference between two transducer halves divided a circular disc transducer. In the calculation result of the angle from the acoustics axis, we show that the window function improves sample the range of TS from 20dB of line array to 50dB of this function array.

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