Study on Effects of Finite-Aperture Transmit–Receive Arrays on Underwater Target Strength Measurements and Error Correction

To address the limited source level of transducers and the insufficient signal-to-reverberation ratio (SRR) and signal-to-noise ratio (SNR) of target echoes in underwater model target-strength measurements, coherent multi-element transmission is commonly employed in lake acoustic-scattering experiments to focus the acoustic field in the target region and improve echo quality. However, because practical deployment distances do not always satisfy strict far-field conditions, the measurement configuration may deviate from the ideal plane-wave incidence and reception conditions, thereby introducing errors into target-strength measurements. In this study, an elastic spherical shell is used as a representative target for method validation. A theoretical target-strength model incorporating multi-element transmission and reception is established, and an extreme gradient boosting (XGBoost) regression model is proposed for measurement-error prediction and correction. The results show that the target-strength deviation caused by finite-aperture transmission generally increases with increasing frequency and element spacing and with decreasing transmission distance, whereas the target-strength deviation introduced by the receiving array is comparatively smaller. The developed XGBoost model captures the dependence of target-strength error on frequency and array parameters, reducing the root mean square error (RMSE) relative to the ideal plane-wave reference by 62.1% to 1.6 dB after correction. Lake experiments further show that finite-aperture transmission introduces deviations from the ideal plane-wave theoretical values, with an RMSE of 3.4 dB under finite measurement distances, highlighting the need to improve the model’s generalization capability for practical correction.