Study On Real-Time Monitoring Technology Of Channel Siltation Location And Height In Shallow Sea

Generally, shallow sea channel has the severe deposition under the weather and hydrology conditions of wind, wave, flow etc. Because of lacking real-time siltation monitoring method, it often appears the economical loss caused by less load or ship grounding and port obstruction caused by excess load. In the paper, a new technology of real-time channel siltation monitoring is presented based on the analysis of characteristics of the shallow sea channel, acoustic propagation and attenuation in the channel. Main contents of this paper are as follows:Based on Ray Theory describing acoustic propagation law in underwater acoustics field, the characteristics of the small grazing angle acoustic propagation in the shallow sea channel is researched on the basis of simplified acoustic velocity distribution. The results show that the sound ray trace can be regarded as a straight line. According to the law of Snell and Conservation of Energy, the characteristics of acoustic wave scattering and transmission on sea surface is studied. The acoustic wave will scatter and transmit when it propagates to the sea surface and the energy of transmission is far less than that of scattering. By comparing scattering coefficient with transmission coefficient, when the high-frequency acoustic wave propagates on the bottom, most of the acoustic energy transmits into the deposition layer and the scattering acoustic energy can be neglected.Sound attenuation model of the polydisperse particle suspension liquid acoustic propagation attenuation loss is derived from Bouguer-Lambert-Beer Law. In the laboratory, the prepared aqueous suspension of ultrafine glass beads and aqueous titanium dioxide of different particle diameters are applied to measure the acoustic attenuation of five ultrasonic frequencies. The result shows that the model is effective. Based on the model and combined with the empirical formula of spreading loss and absorption loss of the acoustic wave in the sea , the acoustic propagation attenuation model in the turbidity sea area is established. The measurement results of the acoustic propagation attenuation in one Bohai sea channel show that the acoustic propagation attenuation loss in shall sea channel relates to particle diameter, particle volume concentration and the acoustic frequency.According to the problems that present siltaion measuring methods and forecasting method in the shallow sea channel can't realize real-time monitoring, a new siltation real-time monitoring method in the shallow sea channel is proposed based on the research results of acoustic propagation in the shallow sea channel and seismic CT structure. It is called Multi-Sensor siltation monitoring method in the sides of channel based on transducer arrays. At the same time, a set of monitoring system is designed. In the method, one set of transmitting transducer array is fixed on one side of the channel and one set of receiving transducer array is fixed on the other side. On monitoring, the transmitting transducer is opened to transmit acoustic wave in turn and receiving transducers are always working. And when the siltation position and the height are different, the power spectrum's peak and the transmission time of the sonar signal are different too. In terms of the difference, the siltation situation in the monitoring area can be judged. Through wireless data transmission module, the monitoring data can be transmitted to the monitoring center in the shore. And applying the Internet, the client can realize real-time monitoring on the siltaion position and height in the shallow sea channel.In order to judging the siltaion position and height, the multi-class problem method of judging the channel siltaion position based on Decision Directed Acyclic Graph Support Vector Machine(DDAGSVM) algorithm and the method of judging the channel height based on support vector machine regression are put forward. Firstly, applying discrete K-L transform, the siltation features vector is extracted. And it can compose siltation location training samples and height training samples respectively with the siltation location and height in the monitoring area. When judging the siltation location, the channel is bisected into some areas along channel width direction, and each area is one type siltation. Between every two classes, one classifier is constructed. With the siltation location training samples, the classifiers are trained. And when the siltation feature vectors are brought in the well trained classifiers and combined with DDAGSVM Algorithm, the siltation location is judged. When judging the siltation height, with the siltation height training samples, the siltation height regression model is trained. And when the siltation feature vectors are brought in the well trained model, the siltation height is judged. The experiment results in anechoic tank and Dalian channel show that in anechoic tank, the judging siltation position precision can reach 3m, and in Dalian channel, it is attained the actual demand of the channel. And in Dalian channel, the judging siltaion height precision can reach 60 mm. Compared with conventional methods of neural network, the methods have better effect, stronger generalization ability and fast decision speed.