The Design Of The Submarine-height-measuring System For The Ocean Exploration Towed

The 70% of the Earth's surface for mankind's survival is covered by the sea. Since ancient times, sea has a decisive effect on the survival and the development for human beings. Seabed resources is the world's largest treasure house, as it's also the world's largest Laboratory for Earth Science, thus the explorations on the seabed have great significances both in the theoretical and practical for the questions which attract attention in many subjects. Explorations of the seabed are mainly used by geophysical methods, the geophysical methods on submarine detections are commonly used into two ways: seismic and electromagnetic methods. The flexible medium wave would be absorbed and scattered when exploration on complex seabed geological structures, the seismic detection results will have considerable impact. The method of electromagnetic is the use of the differences in conductivity for different medias to detect the geological structure within the seabed. Electromagnetic method can be divided into two ways according to whether the electromagnetic source used can be controlled into Magnetotellurics method (detecting electromagnetic field source is not controllable) and Controlled Source Electromagnetic method(CSEM). As the electromagnetic is shielded by the water, the high-frequency part of the natural source has be shielded near the seabed, so it can not be used for Magnetotellurics to detect. Therefore, when mean to explore the seabed, use the CSEM method that set the emission source in or near the seabed. Marine controlled source electromagnetic method(Marine CSEM) is introduced in the mid 80s of the 20th century into the research on the exploration theory of exploring the seabed oil and gas resources. With the development of the electronic technology ,the data processing and interpretation and computer processing technology in recent years, , marine CSEM technology is gradually forming, and become into in a very efficient way for seabed exploration particularly for the source exploration.The paper is for the state Eleventh Five-year Project :"The key technologies in the launches for Marine controlled source electromagnetic exploration " to designed a system for measuring the relative height between the submarine towed body used by the marine controlled source electromagnetic and the seabed. The system's implementation is not only solve the problems that measuring the relative height of the controlled source electromagnetic system working in the deep-sea, but also filled a domestic blank of the measurements of height for underwater towed body. Through the system's demonstration, the height measuring system used the acoustic manner.Sonar is the equipment using the spread of the sound wave in the water to locate and navigate the sailing ships, submarines and the other submarines working in the water. Acoustic propagation in water also have many different characteristics form it's spreading in the air: the propagation speed of sound in seawater is mainly effected by water temperature, the static pressure, the salinity and other factors, the general empirical formula calculation is very complicated, so general calculations use the simple formulas or take the speed of sound in the general value of marine 1500m/s; the transmission loss of sound waves would be great, and would also be impacted by the reverberation; the wave's propagation in the ocean would be impacted by the ship noise from ocean surface and water noise inside the ocean.In the process of designing a active sonar system, each part of the system be designed should follow the active sonar equation, need to calculate the following parameter :the Transmission Loss (TL), the Target Strength (TS), the Sea Noise (NL), the transducer receive Directivity Index (DI) and the Sound Source-Level (SL). The main parameters of the system have the period of pulse repetition, the resolution of pulse range, the maximum and the minimum depths for measuring length.The overall framework of the system can be divided into three parts: the deep-water transducer, the transmitting and receiving circuit and the main control circuit. The system uses pulse range method to measure the height of the submarine completed with the seabed, so the system chose the CW pulse signal as its working signal. According to the system design requirements, chose the system operated at the frequency of 100 kHz. In order to simplify the system, using a monostatic transducer in the place at the front-end and the requirements of the transducer is: working pressure can reach up to 15MPa, the deviation of the center working frequency must be within±2kHz, while the working beam angle is (5±1)°, when the sound working source-level should be≥220dB, and the receiver sensitivity≥-200dB.The main function of the system's main control section is to generate the signal for sounding, the control of the system clock and make a calculation for the measuring of height. To make the whole system more simply and more efficient, using a model of EP1C6T144Q8 FPGA produced by an Altera to complete the whole system ,and the programmatically of the whole system use the Verilog HDL hardware logic programming language as is popular nowadays, the idea according to the Top-Down design. The master section can be divided into: the PLL multiplier module, the CW signal module, the timing module and the calculating module. The CW signal module read lookup table manner: a single CW signal written into the FPGA-ROM being burned, and then read the ROM data in the accumulator to generate the CW pulse signal; the timing module is timing for CW pulse transmission : from the moment CW pulse signal transmission starts timing, stopped after receiving the echo t, and to pass the length of time to the calculation module for the calculation of height, and in order to timing precisely , use high frequency clock count data in the transmission of data on the timing rounding; the calculation module is to complete the drag calculation of the height between the submarine from the bottom, when receives the sound pulses plying time from module the timing, the module calculates the height from the seabed, in a simplified system considered , using fixed point calculations, and the sound speed use the general value c = 1500m/s.System transceiver circuit in the system with the transducer directly connected, Abstract its performance would directly influence the measurement results of the whole system. Transmitter circuit not only converted the CW pulse digital signal to analog signals to from the master section and transmitted and enlarged it to the transducer, but also the need to match the driving of the transducer with the actual working conditions on the transducer; the main function of receiving part circuit is to identify echo signal from the transducer receives and transmitted a signal to the master section to express having received the echo. The transceiver circuit can be divided into three parts: high-speed DA conversion circuit, the transducer matching circuits and the receiving frequency discriminator circuit. As is including: high-speed DA conversion circuit THS5651A to the master part of the output of the CW binary signal is converted to analog signals; the matching circuits on the one hand is to drive the transducer to work, while the other is to neutralize the capacitive reactance in the equivalent circuit of the transducer; the receiving frequency discriminator circuit use a piece of LM567 chip to identify the echo, and also would like to transmit an interrupt signal to the FPGA in the master section that has received the echo, let the FPGA's timing stop and start to calculate.After analyzing the signal process through the system, simulate the pulses signal of the system. Through the analysis the directivity index of the actual using transducer, modeling the process of the pulse signal ranging from, and make the signal flow diagram. Simulate sounding signal of the system, and compared the simulation results and the experimental results.Thesis made a highly detailed argument on the measuring system, and gave a feasible design, and completed some preliminary tests. The next step requires the equipment to carry out more experiments to test the stability of the system work, and system-related improvements.