A New Single DIFAR Sonobuoy Target Location Algorithm

In order to solve the problem of target location of single direction finding and ranging(DIFAR) sonobuoy, a new target location algorithm is proposed. Based on the new generation of high performance sonobuoy signal processing platform, the new algorithm makes full use of the Doppler information of the targets while using the target location data, and successfully implements the target detection, location and tracking. In the calculation of target parameters, the new algorithm utilizes the repeated measurement data to further improve the calculation accuracy of the target parameters using the principle of Least Square. The simulation results indicate the correctness of the new algorithm. The algorithm is simple, stable and easily implemented in engineering. And besides, it overcomes the weakness of the traditional algorithm which requires at least two DIFAR buoys to locate the targets.

Sinusoidal Vertical Motion Suppression and Flow Noise Calculation for a Sonobuoy

The flow noise associated with sinusoidal vertical motion of a sonobuoy restrains its working performance.In practice,a suspension system consisting of elastic suspension cable and isolation mass is adopted to isolate the hydrophone from large vertical motions of the buoy on the ocean surface.In the present study,a theoretical model of vertical motion based on the sonobuoy suspension system was proposed.The vertical motion velocity response of the hydrophone of a sonobuoy can be obtained by solving the theoretical model with Runge-Kutta algorithm.The flow noise of the hydrophone at this response motion velocity was predicted using a hybrid computational fluid dynamics(CFD)-Ffowcs Williams-Hawkings(FW-H)technique.The simulation results revealed that adding the elastic suspension cable with an appropriate elastic constant and counterweight with an appropriate mass have a good effect on reducing the flow noise caused by the sonobuoy vertical motion.The validation of this hybrid computational method used for reliable prediction of flow noise was also carried out on the basis of experimental data and empirical formula.The finds of this study can supply the deep understandings of the relationships between flow noise reduction and sonobuoy optimization.

THE CRUST VELOCITY STRUCTURE OF PROFILE 820 IN THE AREA OF EAST CHINA SEA AND ITS VICINITY

Since 1982, the Institute of Oceanology, Chinese Academy of Sciences(IOCAS) has conducted more than 20 sonobuoy refraction measurement in the area of East China Sea. In 1991, the IOCAS also conducted OBS measurement in the same area. Both the our refraction data and other authors’ refraction data measured in the area of East China Sea have been used to study the crustal velocity structure along the Profile 820 which is across the East China Sea shelf basin, Okinawa Trough, Ryukyu Island, Ryukyu Trench and Philippine Sea in this paper. The ages of the velocity layer have also been determined in this paper.The crustal velocity structure is difference both along the profile 820 and from top to the depth. Along the profile there are three basins and three uplifts. From top to the depth there are 5 velocity layers, which are layers of 1 8～2 2km/s, 2 4～2 8km/s, 3 0～3 6km/s, 4 2～5 1km/s, 5 75～6 0km/s. Based on the velocity structure we can know that the deposit environment was stable between Pliocene and Quaternary along the whole profile except the axis part of Okinawa Trough which had always been active and the deposit florescence was Eocene and the whole area was uplifting in the time of Oligocene and the sediments of that time upon the Diaoyudao uplift and Ryukyu island and also the area of East China Sea shelf basin and Okinawa Trough were denuded. The origination of the East China Sea shelf basin and the Okinawa Trough might be after the deposition of the velocity layer of 5 75～6 0km/s.

PROCESSING AND INTERPRETATION OF DATA FROM A SONOBUOY REFRACTION SEISMIC SECTION IN THE EAST CHINA SEA SHELF MARGINAL RIDGE

Refraction seismic data obtained from a sonobuoy (SB7) in the East China Sea shelf marginal ridge was processed and interpreted. Intercept times and layer velocities were used to set up a one-dimension depth-velocity model based on which a two-dimenssion depth-velocity crustal model was established through two-dimension ray-tracing . The computation results showed that the upper crustal depth-velocity model beneath lineSB7 is composed of four layers with primary wave velocities of 1.80-2.20, 2.85-2.90 3.24- 3.34 and 4.55-6.00 m/s respectively . Neighbouring reflection seismic data and data on the East Chna Sea(ECS) regional geology were used to study the reationship between the velocities and their formation ages and also the contact reationship between the velocity boundaries .