Development of underwater acoustics in China and L. M. Brekhovskikh’s early activities in China Dinghua Guan (Inst. of AcousL, ChineseAcadof Sci, Beijing 100080,China) Summary:In thispaper the early activities and influence of L.M.Brekhovski!xhin the development of underwateracoustics in Chinaare reviewed. The activity of Brekhovskikhin the formulation of the 12- yearplan of S&Tdevelopment of China in 1956is described.This paper reviews the early development of underwateracoustics in Chinaincluding the visit of Chineseexperts to theInstitute of Acousticsin Russia, thefust joint Sino-Russianexperiment in the SouthChina Sea, the trainingof youngChinese scientists, influenceof “Wavesin layeredmedia”. This paper also reviews part of the researchon underwater acousticsin China. EARLY HISTORY It was 43 yearsago since I met with L.M.Brekbovskikb at first time. It was at the period of begiting of People’sRepublic of China. There were only a few researchinstitutes and small number of scientists in China. At that time China was almost isolated from western world. The only partner was Soviet Union and we tied to learn all from them. Our governmentdecided to make a 12-year-planof developmentof sciencesand technology. Greatestemphasis was payedon computertechnique, automation, semiconductors, electronics (include underwateracoustics). At that time there were only a small group of acousticiansin China, and most of them were working in the field of room acousticsand ultrasonics.We knew very little about underwater acoustics and many important parts of research in underwateracoustics were not publishedyet and couldn’tbe found in literature at that time. For working out 12-year-plan of development of sciences and technology, 13 academiciansfrom Soviet Union were invited by Chinesegovernment. Among them L.M.Brekbovskikb was invited to help us in underwater acoustics. At that time I was graduatedfrom Qingbua University and Beijing Institute of RussianLanguage and took part in planningas an interpreter.The plan of developmentof underwateracoustics was discussed independentlyand formulated into a special confidential volume, and was not published openly. The plan included research in shallow water and deep ocean, the research in propagation, reverberation and noise in the ocean, the research in transducers and instrumentationfor underwateracoustic research, the establishmentof researchinstitute in Academy of Sciences,industry and universities,the building of researchvessels, basin for measurementof transducersand instrumentationfor researchin underwateracoustics, and the training of young scientistsin different fields of underwateracoustics. His advicegave a main frame for developmentof underwateracoustics in China. After then, L.M.Brekhovskikh was invited to visite Nanjing University in Nanjing and then to visit Hainanto look at the ocean environmentof South China Sea. Afier then, four institutes of new technologywere establishedin ChineseAcademy of Sciences, namely, Institute of Computers, Institute of Automation, Institute of Semiconductorsand Institute of Electronics. Prof. Wang Dezhaowas appointedas deputy director of Institute of Electronicsin chargeof developmentof underwateracoustics. After establishmentof Institute of Electronics,a group of scientistswas sent to Soviet Union, to visit Institute of Acoustics in Moscow and Laboratory at Black Sea.At that time L.M.Brekhovskikh was director of Institute of Acoustics and had shown all the researchin underwateracoustics. A plan of joint experimentof underwateracoustics in South China Sea and plan of exchangeof young scholarswere signed.After this visit, a largegroup of students graduated (or undergraduate)from Beijing University, Qinghua University and Nanjing University were gatheredto form an underwateracoustics laboratory leadedby Prof. Wang Dezhao. “Waves in layered media”, and “Physics of sound in the sea” were text book for theseyoung scholars. In year 1958,Prof. Suharevskyarrived to China for preparementof joint experimentand soon afterward Dr. Mazepov and a group of russian scientistsarrived to South China Sea. Many instrumentswere conveyedfrom Russian.Joint experimentwas conductedby russian scientistsand group of Chinesescientists from Academyof Sciences,universities and industry. It was the first experiment in underwater acousticsin China seas. This joint experiment includedpropagation, reverberation, scattering, fluctuation, and measurementof absorptionof soundin seawater. In laboratory of underwater acousticsin Institute of Electronicsthere were groups of researchin propagation,reverberation, scattering, measurement of seawater soundabsorption, measurementof underwateracoustics materials, very similar to thesein Institute of Acoustics in Moscow. A group of young scholarsstudied in Institute of Acoustics in Moscow in the field of underwateracoustics. The situation changedvery soon, and afterward China conductedresearch in underwater acoustics,isolated from outer world. But influence of suggestionof L.M.Brekhovskikh, his book “Waves in Layered Media”, the joint experimentand the visit and training of young scholarsin Institute of Acoustics in Moscow had large influence on researchof underwater acousticsin china for a long period. Due to importance of shallow sea in China, almost all the work in underwaterat this period was concentratedin shallow water. Many interestingphenomena were discovered. PROPAGATION OF SOUND IN SHALLOW WATER Shangand Zhang give the expressionof normal modes in terms of reflection loss and cycle distanceincluding displacementat seabedreflection. [Shang 1961,Zhang 19651.Zhang has further develop this theory and gives accurateformula for attenuationand group velocity of normal mode and developedto a BDRM method, which can be used in fast computationof soundfield [Zhang 19811and developedfor strong range-dependentshallow water. Brekhovskikh [ 19571and others studied the averagefield in inhomogeneousshallow water and proposedintegral expressionsof the averagesintensity. Zhang [19811 used a generalized phased-integralapproximation to overcomedifficulty of divergence. In Yellow Seadue to many condition strong and sharp thermoclineoccurs in s-er time. Zhanget al observedand explainedregular multipath structuresof pulse signals. In the Yellow Seain the summertime, abnormalattenuation of soundpropagation loss at the frequency range between 300Hz and 12OOHzhas been observed. It is shown that the abnormallylarge transmissionattenuation can causedby “acoustic mode-coupling”loss due to the interactionof internal wave packets[Zhou et al 19911. Shang and Zhang has discussedhorizontal coherenceof sound due to surface waves and temperaturemicrosturcture.. Zhu and Guan madeanalysis of horizontal coherenceof different modein shallowwater [1992] REVERBERATION AND SCATTERING IN SHALLOW WATER In China, theory for generalcases of reverberationin shallow water was developed[Zhang and Jin, 1987,Zhou et al, 19821.A key feature is to decomposeeach mode into up-goingand down-goingwaves. The scatteringis presentedin terms of a mode-coupingmatrix, empirical scatteringfunctions are employed.Ray mode analogiesare used to calculatethe scattering angles,and a new normal-modeanalogy is developedto computethe scatteringarea in term of modal parameters.A radiationby a directionalsecondary source at eachscattering area and a re-transmissionto the receiver. It was proved that the bistatic reverberationintensities is the geometricmean of reverberation intensities of source and receiver depth [Zhang and Jin 19871. Under small Rayleigh’s parameterapproximation the relationship between plane wave and wave guide scattering coefficient was found [Gao 19891. MODES AND RAYS Experimentsof mode filtering were conductedin mode1tanks and at the sea in China. Matched mode processingmethod for source ranging and depth estimation was suggested [Shang, 198.51.A strict Fourier transformationbetween rays and modes was proved by Gao and Shang[Gao and Shang,19831. INVERSE METHOD AND REMOTE SENSING Some inverse methods for calculating the reflection bottom loss are proposed: from transmission loss curves [Guan,l979][Wang and Zhang 19891, from vertical correlation coeffkient [ Zhou,l979]. Basedon the dispersionanalysis of explosivesound, bottom sound velocity of a fluid half spaceis obtained. To extract information of surficial sea-bedsediment measure“tails” of reflected signals normally incident high frequency sound pulses to estimate sound attenuation in sea-bed sediments meng and Guan, 19821. Liang and Lu have studied the physico-mechanical propertiesof continentalshelf seabed sediments. Many instruments for remote sensing of ocean environmentswere developed, such as Doppler current profiler, subbottomprofiler, color image sonar, side scan sonar, instrument for measuringsuspending particles in water, satellitebuoy, and etc. RFERENCES 1.Bre!&ovskikh L.M., Wavesin LayeredMedia, AcademicPress. 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