| Directivity is one of acoustic characteristic parameters for sonar receiving arrays,and it is an important indicator to measure whether the resolution is standard or not.In order to enhance the working range of the sonar system,the working frequency of the sonar receiving arrays decreases and the size increases.Therefore,the existing measurement methods are difficult to achieve directional measurement of free field and meet the far field measurement conditions.In addition,the directivity parameters of the sonar receiving arrays change due to various practical factors after the installation of the real ship.In view of this,this paper proposed a ship-board calibration method for the directivity of sonar receiving arrays,which realized the accurate measurement of the directivity of the sonar receiving arrays on the real ship.The advantages and disadvantages of the existing measurement methods were comprehensively analyzed,and the calibration method of directional measurement of sonar receiving arrays was designed by flexible lifting measurement system in open waters.Based on the ultra-short baseline positioning technology and coordinate transformation algorithm,the position and attitude of the measurement system could be obtained.After collecting and processing the voltage signal,the directional measurement could be realized.In order to improve the positioning accuracy,the array elements spacing was expanded,and the linear frequency modulation pulse signal and pseudo random coding pulse signal were selected in the signal form,the distance and phase measurement were realized based on pulse compression method and complex correlation method respectively.In order to verify the feasibility of the calibration method,the measurement system was built,and the positioning accuracy verification test and method feasibility test were designed and carried out in the lake test field.The method feasibility test was divided into the static test based on the standard measurement method and the dynamic test based on this measurement method.The experimental results showed that the improved positioning method has higher positioning accuracy and stronger anti-environmental interference ability.The directional results measured by the standard measurement method were used as the standard values,the errors of the directional results measured by this measurement method were within 5.38 %,which meeted the requirement of measurement error less than 10% in directional measurement standard.And the feasibility and effectiveness of the calibration method of directional measurement of sonar receiving arrays were proved. |
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