| Ocean is rich of natural resources, and is a huge of geology research places.China has more than3million square kilometers ocean land area. In recent years,ocean’s huge economic value and important traffic strategy status caused strongconcern and attention in increasing national and area. Regardless South Sea disputeIsland friction also Diaoyu Island sovereignty problem are showing the importance ofocean resources. Ocean exploration is the important means to get ocean traffic,fisheries and energy resources. China has vast maritime areas, and with thedevelopment of science, people begin to explore and study the ocean, need to putseismic wave method instruments, electro-seismic exploration instruments and otherhigh-end exploration instruments to sea. The exploration equipment’s placement isvery stringent, and the exact arrangement is the prerequisite for using instruments. Atthe same time the location of the instrument, as one of the important physicalquantities, must be used to interpret the exploration result. And if we could not recyclethese valuable equipment, the cost of research will be raised to a large extent. So, theaccurate placement and recovery of such high-end equipment are very important.Undersea seismic exploration, ocean magnetotelluric exploration and ocean controlledsource electromagnetic exploration need to put the observation instruments to thebottom of the sea. The instruments begin to record data according to the requirementsof the appropriate methodology. After the mission completed, the equipment will floatup to the surface from the bottom according to the instruction, and transmit recoverysignals. Because of the sea currents, the deviation of instruments may have negativefactors for data processing; In addition, the sea currents may drift away theinstruments and cause heavy economic loss. So, the research of instrumentsunderwater positioning technology is of great significant.Because of electromagnetic wave shielding effect of seawater, instrument electromagnetic information could not be obtained at the bottom of sea. Sound wavewhich is one of the ocean’s physical quantities spreads farthest. Underwater acousticequipment is often used on ocean exploration. Through the principle, technology,feature and background of ocean controlled-source electromagnetic, we designed theactive short baseline sonar systems, using40kHz ultrasonic as the working frequency.Through basic physical properties and classification of acoustic research, we analyzethe model of sonar and acoustic wave propagation in seawater speed characteristic,and study Ocean acoustic channel and water absorption of the acoustic transmissionloss. Through the study of acoustic positioning mode and active sonar equation, wedetermine the active working mode as positioning. In order to describe the structure ofthe seawater clearly, we suppose it as layered media. According to practicalmeasurement features we select short baseline positioning method for the system.Based on the principle of acoustic positioning and the sound velocity empiricalformula, we get the location algorithm of the system.Hardware design of positioning system consists of four parts: transducer and itsmatch circuit, transmitter circuit, receiver circuit and control circuit. Based on theknowledge of transducer and the active sonar equation, WBT-30is selected as thesystem sending and receiving transducer. DC inverter is used to improve the amplifiedsignal power. Receiving circuit is designed with amplifier and filter. After theanalog-digital, MSP430with low-power mode could operate the signal. Experimentsare conducted in seawater pool and the measured waveform are given. At last it is theerror analysis. |
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