The retrospective method of fixing trailer value with short base line is developed

0 Introduction

Ultra-short baseline underwater acoustic locator (hereinafter referred to as "underwater acoustic locator") is the basic equipment for water transportation research. Its working principle is to install acoustic beacon on the underwater target to be located, and install ultra-short baseline array on the hull above water. The acoustic beacon sends out acoustic signals, and the underwater acoustic locator energy exchanger can measure the distance of the target after receiving the signal. Because the rapid attenuation of radio waves in water renders GPS useless, Acoustic wave is the most effective underwater long-distance transmission information carrier at present, so underwater acoustic locator has been used more and more widely in the field of ocean and water transport, such as ocean exploration research and resource development, maritime rescue search, wreck salvage, cable layout and other aspects are indispensable to the underwater acoustic locator to provide high precision and high quality positioning data. However, due to the complex and changeable use environment, instrument performance changes and other factors, often lead to the failure or loss of measurement results, to the ocean, water transport research work has brought huge loss of human and financial resources. In the actual use of underwater acoustic locator, due to the lack of professional measurement calibration system, domestic and foreign researchers can only recognize the manufacturer's "nominal" performance indicators and detection ability, or can only carry out test comparison or self-calibration method, lack of accurate evaluation of underwater acoustic locator measurement performance. In this case, the accuracy of the measurement results of underwater acoustic locator will have a great impact on the construction quality, investigation, design and model test results of ocean engineering and water transport engineering. Therefore, it is particularly important to test and evaluate the measurement performance, reliability and applicability of the instrument by various means regularly.

Based on the ship lock pool of Tianjin Port, this paper proposes the measurement and traceability method of the slant distance of underwater acoustic locator based on the designed multi-dimensional operation control mechanism, which will fill the gap in the measurement and detection technology of underwater positioning system and escort the research of underwater positioning.

1. Structure and working principle of underwater acoustic locator

The underwater acoustic locator is mainly composed of underwater acoustic measuring equipment and above water data acquisition and processing equipment. The underwater acoustic measuring equipment is composed of the transducer array installed in the hull and the acoustic beacon installed in the underwater mobile carrier. The structural diagram is shown in Figure 1. Acoustic transducers transmit acoustic signals to acoustic beacons, which transmit a response signal different from the interrogation signal back to the transducer after receiving the interrogation signal, and the response signal is transmitted to the deck processing unit through the communication cable.

The selection of measuring standards and supporting facilities shall follow the following principles:

(1) There are relevant metrological verification regulations and national standards for underwater acoustic locator, and the selected metrological standard should meet or be better than the requirements in the technical documents;

(2) Instruments and equipment that have a great impact on the measurement results, such as the sound velocity profiler used for sound velocity correction in the measurement process of underwater acoustic locator, should be effectively traced.

The design parameters of the underwater acoustic locator calibration system are as follows:

(1) Multi-dimensional operation control mechanism The multi-dimensional operation control mechanism designed in this paper includes horizontal shift, lifting, rotating and switching flange, among which the horizontal shift part realizes long-distance horizontal movement along the guide rail with the test vehicle, and the running speed is 0.6m /s. The lifting part realizes the precise position control of underwater acoustic locator transducer and acoustic beacon in the vertical direction of water surface. The rotating part realizes the horizontal rotation movement of underwater acoustic locator; The switching flange is used for the mechanical connection between the multi-dimensional operation control mechanism and the underwater acoustic positioner. The physical diagram of multidimensional operation control mechanism is shown in Figure 2.

Figure 2 Multidimensional operation control mechanism

(2) The maximum allowable error of the sound velocity profiler is 0.2m /s, which provides the standard sound velocity value for the underwater acoustic locator, as shown in Figure 3.

Figure 3. Sound velocity profiler

(3) The accuracy level of the steel tape is 1, and the model is 5 m. The steel tape that has been checked is used to calibrate the running track of the multidimensional operation control mechanism.

3 Calibration method

The steel tape was used to calibrate the track scale of the multidimensional operation control mechanism, the resolution was 0.01m, and the distance was 0-180 m. The underwater acoustic locator transducer is vertically fixed on the lower end of the lifting sleeve of the left multi-dimensional operation control mechanism through the conversion flange, and the rotating horizontal rod folding rotating shaft makes the underwater acoustic locator transducer located 1m below the water surface and not less than 3m offshore; The sound velocity of different water depth points is measured with the measured sound velocity profiler, and the standard sound velocity value is input to the transducer of the underwater acoustic locator to correct the sound velocity parameters of the underwater acoustic locator. Same as the transducer of underwater acoustic locator, the acoustic beacon is placed 1 m below the water surface through the right multi-dimensional operation control mechanism, and the distance between the acoustic beacon and the side wall of the pool is kept the same as that between the transducer and the side wall of the pool. Keep the left multi-dimensional operation control mechanism located at the zero scale line of the track, slowly move the right multi-dimensional operation control mechanism, and select 5m,100m,150m as the calibration point of the oblique distance of the underwater acoustic locator; The measured value Z= 10 times of each oblique distance of the underwater acoustic locator was recorded, and the average value 7 was taken as the measured value of the oblique distance. The error of the indicated value of the oblique distance was calculated according to Formula (1). Oblique distance calibration principle of underwater acoustic locator is shown in Figure 4.

Where, AL is the deviation (m) of the value indicated by the oblique distance of the underwater acoustic locator being calibrated; i is the deviation measurement value of the calibrated underwater acoustic locator (m); Is the standard deviation of the calibrated underwater acoustic locator.

1- Running track; 2- track scale; 3- left multi-dimensional operation control mechanism; 4- right multi-dimensional operation control mechanism; 5- pool side wall; 6- Measurement value of slant distance

FIG. 4 Schematic diagram of slant distance calibration

4 Calibration results

Rang-2 underwater acoustic locator was selected as the test prototype to carry out oblique distance calibration test according to the aforementioned calibration method. Figure 5 shows the measured results of the data acquisition software at 5m from the transducer to the acoustic beacon. The results of calibration are shown in Table 1. As can be seen from Table 1, the deviation of Ranger-2's deviation value increases with the increase of deviation, and the deviation of each calibration point is less than the maximum allowable deviation of deviation ±(0.5+Rx3%) stipulated in JJG(Traffic) 152-2020 (Ultra-short line Underwater acoustic location Instrument), where R represents the deviation measurement value.

5. Evaluation of measurement uncertainty

To verify the reasonableness of the proposed calibration method, the measurement uncertainty evaluation was carried out for the above test method and test results.

5.1 Mathematical Model

5.2 Synthesis sensitivity coefficient

5.3 Calculate component uncertainty

The measurement uncertainty is the measurement uncertainty introduced by the calibration equipment, and the main influencing factor is the measurement uncertainty component introduced by the measurement repeatability. In the process of measurement uncertainty evaluation, the data collected by the underwater acoustic locator when the standard skew distance is 100 m are used as representative data to carry out measurement uncertainty evaluation. The measurement data are repeated for 10 times, as shown in Table 1. The standard uncertainty is calculated by Class A evaluation method of measurement uncertainty, and the standard deviation is calculated by Bessel formula to calculate the measurement uncertainty of the mean.

When the standard skew is 100 m, the standard deviation S of the measured data is 0.32 m, and the measurement uncertainty introduced by the repeatability of skew measurement is

5.4 Uncertainty of synthesis standard

5.5 Extended Uncertainty

Taking the extension factor k=2, the extended uncertainty is U = k x u(△l) = 0.20 m

5.6 Report and expression of the most uncertain degree

The slant distance measurement uncertainty of underwater acoustic locator is 17 = 0.20 m (4 =2), which is less than 1/3 of the maximum allowable absolute value of error of the measured instrument. It is reasonable to meet the requirements of qualified judgment of measurement uncertainty.

6 Conclusion

With the increasing application of underwater acoustic locator, its calibration demand is increasing, and it is urgent to carry out the measurement research of the corresponding instrument. This paper introduces the structure and working principle of the underwater acoustic location instrument, puts forward the calibration method of the underwater acoustic location instrument, and chooses the prototype to carry on the test measurement, and obtains the deviation indicating value of the measured instrument. The results of measurement and the uncertainty of measurement accord with the specified index, which verifies the feasibility and rationality of the method.

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