Progress and Prospects of Hydrographic Surveying Technology ’in China

By Huang Motao, Zhai Guojun, Ouyang Yongzhong, Liu Yanchun and Lu Xiuping, Tianjin Institute of Hydrographic Surveying and Charting, P.R. of China, China

During the last decade, significant ity. In recent years, with the improve­ advances have been made in the study ment and development of computer of hydrographic surveying technology in technology and information acquisition, China. This paper gives an outline of an outstanding change has also recent progress in the fields of survey occurred in the branch of marine sur­ equipment, information acquisition, veying. Besides traditional hydrogra­ data processing, data management, phy, many new branches of marine sur­ basic survey theory and their applica­ vey, such as marine control survey, tions. The future development trends marine engineering survey, seabed are discussed and presented. topography, marine gravity and marine magnetism survey, have shown their value. Three areas of technology, i.e., Introduction airborne laser hydrography, shallow water multibeam depth echo sounding With the development of modern com­ and digital side scan sonar, are puters, as well as space and communi­ thought to be the newest technology cation technology, significant changes for shallow water hydrographic surveys have taken place in surveying and owing to their high speed and high res­ mapping science and techniques, from olution. The application of this new its theory to its application. As early as equipment has resulted in an impor­ 1990, the International Union of Sur­ tant change from point and line survey veying and Mapping (IUSM), gave a new mode to swath measurement. Breaking definition to surveying and mapping. through the traditional limit of time and Namely, that, it is a branch of science, space, marine surveying has at last engineering and technology, which advanced to a new stage where digital deals with the acquisition, measure­ survey methodology, computer technol­ ment, processing, analysis, explana­ ogy and 3S (GPS, GIS, RS) technology tion, description, distribution, usage plays an important role. In the past few and evaluation of geo-spatial informa­ years, significant progress has been tion. Marine surveying is an essential made in the study of hydrographic sur­ part of surveying and mapping science vey technology in China. They are and technology, and its major mission briefly summarised in the following: is to measure and describe the para­ (1) There is an increase in the different meters of ocean geometry and physic. types of survey equipment available. Its purpose is to provide information on (2) In data acquisition and collection, ocean space, required for human activ­ there has been a change from ana- logue recording to digital and automatic recording. beam echosounding system was developed suc­ (3) In data processing, a change from manual pro­ cessfully in 1997 by Haerbin Shipping Industry Uni­ cessing to automation has occurred. versity and deployed in the following year. The (4) Standardisation and the development of net­ H/HCS-017 echosounder comprises a transducer working have been emphasized in data man­ array, a transmitter subsystem, a receiver subsys­ agement systems. tem including beamformer and special digital signal (5) More attention has been turned to application processors, a bottom detector unit, and an operator in the study of basic survey theory. unit for data transfer with external interfaces. The complete mapping system also includes the addi­ tional units: (1) vessel motion sensor; (2) position­ Progress in Survey Equipment ing system; (3) sound speed sensor; (4) postpro­ cessing system. The H/HCS-017 system operates Multibeam Depth Echosounding Technique at a frequency of 45 kHz. It has 48 beams with a The multibeam echosounder is a relatively new type beamwidth of 2° across-track and 3° along-track. of hydrographic survey system with high accuracy, The system is designed to operate in water depths high resolution and high efficiency. It is designed for from 10 to 1000 m below the transducer. It has a mapping 100% of the seafloor. In recent years, swath width of up to 4 times the water depth. The multibeam echosounding systems, especially shal- swath angle is 120° degrees. The H/HCS-017 sys­ low-water mapping systems, have been developing tem is capable of meeting the present IHO stan­ rapidly for various applications, from hydrographic dards. The successful development of the H/HCS- surveying to underwater inspection, from mine hunt­ 017 system has shown that China had achieved a ing to shoreline studies. Multibeam echosounders great step forward in the study of hydrographic sur­ are quite different from conventional single beam vey equipment (Chen, 1999; Zhu, 1999). echosounders, in their principles of operation and According to the need for modern hydrographic sur­ also in the way they are constructed. Unlike conven­ vey development, the International Hydrographic tional single beam echosounders, the multibeam Organization (IHO) promulgated a new version of the depth echosounder is a complex survey system in hydrographic standard, namely IHO S-44, at the which multi-sensors are used. Seabed topographic International Hydrographic Conference in Monaco in survey technology has made great progress owing to September 1994. 100% coverage of the seafloor is the development of the multibeam depth required in the new edition of the IHO S-44 standard echosounder (Mccaffrey, 1981; Tyce, 1986; Atanu for the higher orders of hydrographic surveying. In and Saxena, 1999; Li, 1999). order to meet the requirements of different users, In order to meet the requirements of different the manufacturers of multibeam equipment are mak­ marine activities, China began to introduce multi­ ing a great effort to develop sounding technology for beam depth sounding systems from abroad in the full ocean depth, higher resolution, higher accuracy, early 1990’s. To date, many types of such system and modular and integrated concept design (Huang, exist, including the new generation products, which Zhai, Ouyang, et al., 2000). It should be noted that have been extensively taken into use in marine sci­ during the last decade multibeam technology has ence research, marine resource and environment improved technically, the price level has dropped, investigation, hydrographic surveying, marine engi­ and the system electronics has been made much neering projects, port maintenance, monitoring of more compact. It can be said that multibeam tech­ geologic catostrophy investigation and under water nology has now advanced to a stage where many archaeology. They are playing an important role in users will benefit from taking it into use. The main the sustainable development of the economy and motivation for going from single beam echo sound­ society of China. Since the middle 1980’s, China ing to multibeam echo sounding is the capability to has been involved in the study of multibeam produce maps of much higher quality and with much echosounding systems. During that period, only a more details than previously, with a high productivity prototype was developed and some tests have been rate and reduced cost per area unit. Although the made. No practical products were developed due to capital cost of multibeam echo sounders is higher technical and funding reasons. In the early 1990’s, than for conventional survey echo sounders, they China began to invest again in research of multi­ produce maps at lower cost than before, and with beam echosounding systems. The H/HCS-017 multi­ better quality. The quality of the maps is higher, not because each sounding is more accurate, but propose that the manufacturers of multibeam because of the dense sounding pattern. The dense equipment and other organisations consider the soundings reveal aii the significant underwater fea­ need for uniformity of data format and post-pro­ tures, and eliminate the large errors generated by cessing software in order to get a rapid develop­ having to guess (or interpolate) what the seafloor is ment for the multibeam technology. like between the survey lines. It is because of these facts that more and more hydrographic institutions Airborne Laser Sounding Technique and other organisations are considering replace­ The application of lasers to hydrography was pio­ ment of their existing equipment for mapping the neered in Australia during the 1970’s and 1980’s shallow seabed by the new generation of multibeam by the Australian Defence Science and Technology systems. Now on the international market of multi­ Organisation. This work opened up a new field for beam echo sounder, almost every manufacturer hydrographic survey, i.e., the airborne laser sound­ claims that its product adheres to the most accurate ing technology (Wehr and Lohr, 1999; Baltsavias, IHO standards for hydrographic surveys. That is to 1999).Airborne laser depth sounding (lidar bathy­ say that the new generation of equipment is ideal for metry) is thought now to be one of the most prom­ hydrographic surveying today. The trend in this field ising techniques for rapid and high density sound- is toward making the systems of lighter weight so ing of shallow waters because of its high mobility, that they can be deployed on smaller vessels and cost effectiveness and easy administration due to capable of collecting accurate data at higher speed. a low need of manpower (Andrew, et al., 1998). In It should be noted that, with the development of China, work for testing the principle of operation for modern digital computer technology and other pow­ airborne laser depth sounding has taken place erful techniques, the hardware configuration of the since the middle 1980’s, but did not advance to a new generation mutibeam echo sounder has now practical stage until the middle 1990’s (Tang, at last advanced to a stable stage. In many coun­ 1998; Guan, et al., 1999). The Shanghai Institute tries multibeam survey equipment is now the stan­ of Precise Optical Mechanism has been involved in dard tool for seabed mapping . The difference in the development of airborne laser sounding sys­ basic mechanical design features of multibeam tems since 1997. A prototype machine was pro­ echo sounders from different manufacturers has duced in 1999. The system was installed in a heli­ become smaller and smaller. In such a case, from copter, and some trial surveys over the sea were a hydrographer’s point of view, the most important carried out in 2000. The Chinese airborne laser problem which remains to be resolved is: how such sounding system is called Airborne Laser Sounding a high volume of data from a multibeam system, and Mapping System (ALSMS). It is comprised of a particularly in the case of very shallow water, be laser depth sounder subsystem, dynamic position­ managed and processed effectively from raw ing subsystem, data acquisition and control sub­ sounding data to the final map? With modern, high­ system, ground analysis and processing subsys­ speed workstations available today, the data pro­ tem, and flight support subsystem. The key cessing capacity has increased to such a level that specifications of ALSMS are designed to be: it is sufficient to support the needs for cleaning Laser pulse rate: 200Hz. and editing multibeam data, and for chart compila­ Operating altitude: 500 m (variable). tion. While the capability to visualise multibeam Operating speed: 60 to 100 m/s. data in near real time has become standard for the - Sounding density: 10-m grid (variable). 2D case, a more recent development is the capa­ Scan swath width: 240 m. bility to display the seabed terrain in 3 dimensions Maximum depth: 50 m. as the data is collected. In China, the first nation­ Vertical accuracy: ±20 cm. ally produced multibeam system mentioned has Horizontal accuracy: +5 m (DGPS). just been deployed operationally. There still exist Survey rate in excess of 50 square kilometres many problems to be studied, where improvement per hour. should be made in this new sounding system in Data processing and mapping technology is an order to increase the accuracy and reliability of important part of ALSMS. During the development sounding. The data processing is most significant of ALSMS, many key techniques involved in data to the H/HCS-017 system. As to the application processing and mapping, such as the dynamic and management of multibeam sounding data, we effect of the carrier’s attitude, the corrections for tide and wave, the quality control of sounding data, effort to improve the stability and reliability of the data fusion of neighboring swaths, and so on, AIASHS. With the rapid development of computer have been studied in detail. For production of accu­ technology and the introduction of new positioning rate bathymetric maps with full control of the map instruments, different new styles of AIASHS have accuracy, it is necessary to post process the col­ been developed successively in China to meet the lected sounding data. For this purpose, a software increasing needs of rapid and high precise sound­ system, which includes the necessary software ing and charting. A multifunctional AIASHS was modules for data post-processing, has been devel­ developed by the TIHSC in 1990, which can fulfil oped for ALSMS (Huang, et al. 2003). The system automatically the acquisition, recording, merging is designed to treat the high volume data sets in a and processing of sounding and positioning infor­ block-wise manner, each block being of a size mation from different types of sensors (Guan, which is optimal for efficient processing by the 1991). In addition, the multifunctional AIASHS has workstation. The results of data from the software the function of assisting navigation. It has already system are finally exported to terrain modelling been used widely in large scale hydrographic sur­ and cartographic system. veying, pipe laying on the seabed, harbour and As a new complementary technique for shallow channel dredging, profile surveying and marine water hydrographic surveys, ALSMS will be used in resource investigation in China. After several years combination with the conventional acoustic or of applications, modular, standard and portable mechanical methods. The optimum and most eco­ designs for AIASHS are desired in following years. nomic way of combining these different techniques Such an AIASHS has been developed by the TIHSC will be gradually developed from future experience. in 1995 (Zhao, 1998). It possesses the functions Chinese hydrographers will continue to be actively of planning survey lines, automatic navigating, engaged in data quality assurance, system acquiring and recording data, monitoring data qual­ upgrades, and advanced algorithm development. ity, and processing data and compiling raw maps. Chinese scholars are making a great effort to Automatic acquisitions and merges of different enhance the laser pulse rate and the capability of information from a hydrographic survey can be minimum survey depth of the system. Their targets realised in the new AIASHS. During the survey, one are 1,000Hz of laser pulse rate and 0.5 m of min­ can use the real-time displays to verify if the whole imum survey depth. The introduction of ALSMS survey area has been covered by soundings. The means that China attaches great importance to the comparison between results from different over­ application of aerial remote sensing technology in lapping or crossing survey lines can be used to hydrographic surveying. assess the quality of collected sounding data. The trend in this field is toward making the func­ tions of AIASHS more integrated, and the system Progresses in Information Acquisition to be of lighter weight so that it can be deployed on Technology smaller vessels. At present, Chinese scholars are devoting themselves to the development of meas­ Information acquisition technology is an important uring precise height from RTK-GPS measurements. step in the process of hydrographic surveying. Their purpose is to develop a new type of AIASHS China began to pay attention to research of auto­ using GPS height to eliminate the effects of tide, matic information acquisition systems for hydro- wave and dynamic draught. Such a system will be graphic surveying (AIASHS) in the early 1980’s. An very useful for providing accurate hydrographic sur­ offshore automatic information acquisition system veys of inshore, harbours and channels. for hydrographic surveying was developed success­ fully by the Tianjin Institute of Hydrographic Sur­ veying and Charting (TIHSC) in 1985 and put into Progress in Data Post-processing use in the following year (Guan, et al., 1988). It Technology marked the beginning of a new era where the con­ ventional operating manual mode for information The level of survey data processing technology acquisition of hydrographic survey would be directly affects the quality of survey data results. replaced by a new automatic one. Since then, Chi­ Having finished the development of an automatic nese researchers have been making increasing information acquisition system for hydrographic surveying, the TIHSC began to pay attention to the has been suggested, with which the correction of procedure of data postprocessing. A Hydrographic the tide level for multi gauge stations can be carried Survey Data Processing and Mapping System out successfully (Xie, et al., 1988). For the reduction (HSDP&MS) was developed successfully in 1999. of sounding data to the sounding datum, the tidal It has subsequently been improved and perfected. range ratio method and the least-square fitting The HSDP&MS consists of a sounding data post­ method are proposed to transfer depth datum (Liu, processing subsystem and data visualisation sub­ 2000). In the study of quality control and reliability system. The sounding data post-processing sub­ of sounding data, Chinese scholars have introduced system has the following functions: the theory of robust estimation to the data process­ Input of collected data. ing of hydrography for the first time. A robust method Automatic deletion of different types of blunder. for the detection of abnormal data (including blun­ Automatic detection of abnormal data using ders) in hydrography has been suggested in this robust method. field, which is called the robust interpolation com­ Position processing (including instrument off­ parison test based on robust M-estimation by an set correction). iterative calculation procedure (Huang, Zhai, Guan, Sounding data editing and cleaning. et al., 1999a; 1999b). In order to compensate for Depth correction (including corrections for the systematic errors in hydrography, Chinese schol­ draught, sound speed, tide level, and datum of ars began with a valid significance test of systemat­ soundings). ic error based on variance analysis. Formulas of Compensation and test of systematic error. compensating systematic errors located in the sur­ Evaluation on the quality of sounding data. vey area and survey lines were first derived (Huang, The function of the sounding data visualisation 1990; 1985). In the second stage of the study, fil­ subsystem primarily includes , terrain modelling, tering position data, as viewed from geometrical 3D and contouring. It can provide a variety of final field, was suggested to provide an optimal estima­ products (contour charts, hydrographic symbols, tion of position data. A new model of compensating fair sheets, 3-D presentations, etc.) in the form of systematic errors was then developed, which took maps and charts. Detailed functions are as fol­ into account both direct and indirect influence of lows: ship navigation as well as sounding noise (Huang, Construction of sounding map border. 1992; 1993; 1995). In the third stage of the study, Input of sounding data acquired from survey a self-calibrating adjustment model of compensating field, and coastline data. systematic errors in a more extensive sense, as Transformation of coordinates. viewed from the physical field, was presented Redisplay of sounding data. through the construction of an error model (Huang, Editing of surveying track chart, sounding data Guan, Zhai, et al., 1999a; 1999b). Finally, for prac­ chart, nature of the bottom information chart. tical applications, the rigorous methods mentioned Generation of 3-D map for quality control of above have been simplified in a procedure of two sounding data. steps processing (Huang, Zhai, Ouyang, et al., Generation and editing of contour map. 2001a; 2001b; 2002a; 2002b). Some successful Editing and modifying of other factors. experience in applying computer technology to chart­ - Acquisition of sounding from digital instrument. ing, such as the preparation of a digital mosaic of Output of final hydrographic products. cartographic sources and the automatic drawing of In the HSDP&MS, some of the new theories and very complicated irregular symbols, have been also methods for data processing have been applied obtained in practical applications. successfully. For the sound velocity correction, many Many corrections in data processing are required sets of oceanic water temperature and salinity over for environment effects owing to the characteristic many years were collected. The corrections of sound of real-time dynamic observation in hydrographic velocity in the Chinese sea area were then comput­ surveying. It is believed that the frequency and ed by using hydro statistics, which can be used in inconsistency of different corrections are the main hydrographie survey for both shallow and deep water reason of introducing systematic errors. The accu­ (Shen, et al., 1995). With respect to the correction rate calculation of corrections for environment for tide level, a so-called phase angle difference effects remains to be studied in data processing of method, based on the theory of signal processing, hydrographic surveying. These corrections include beam-width effect in single-beam sounding, addi­ ing technology, and so on, have been applied in the tional sound speed errors in multibeam sounding, development of the system. It integrates the func­ wave effect in airborne laser sounding, magnetic tions of acquiring, managing, processing, analysing, effect of vessel in marine magnetism, and so on. improving and producing the hydrographic informa­ During hydrographic surveying, the three types of tion (data). The detailed development targets are error, i.e., blunder, systematic error and noise, are summarised as follows: present at the same time. Although considerable (1) Establishment of data base systems with multi­ effort has been made in the study of errors in factors of hydrographic survey. sounding data, it is important that one has some (2) Development of specialised software interface knowledge about distinguishing the different error for digitising the paper graphical products and models and adjustment systems. It is useful to find realising the digitisation management applica­ a valid method in which it is expected to compen­ tion of history survey data. sate systematic errors and delete blunder simulta­ (3) Opening of network transmission way of infor­ neously (Li, 1988). Many problems of theory mation in hydrography. remain to be resolved in this field. (4) Development of statistical analysis software. (5) Establishment of network distribution system of information and its products in hydrography. Progress in Data Management The data base system mentioned above consists Technology of four parts, i.e., hardware component, commer­ cial data base system, specialised data base man­ Constituting a valid management system for hydro- agement software, and specialised application graphic survey information is the basis of giving full software. The hardware platform and its options play to the use of sounding data. As early as the late include: net-server, high performance worksta­ 1980’s, Chinese scholars began developments of tions, net-exchanger, Scanjet, digitiser, plotter, and hydrographic survey data management technology printer. 0racle9.0 is used as the commercial data and its applications. As to the constitution of a stan­ base system. The specialised data base manage­ dardisation system, many technical specifications ment software covers almost all the sub-branches for hydrographic surveying data management and its of marine survey, such as coastal topography, sin­ applications have been presented and published gle beam sounding, multibeam echosounding, during the past few decades. Uniform demand on ocean tide, marine gravity, marine magnetism, side the classification, encoding and formatting of hydro- scan imagery, and stereophotogrammetry. The graphic survey information has been included in the specialised application software is comprised of standardisation system (Zhai, et al., 2001). As to data processing modules corresponding to the sub­ the establishment of entity, a few data base sys­ branches of marine survey mentioned above. The tems with single factor of hydrographic survey have system is the first set of management entity of been built independently in succession. Such a data hydrographic survey information in China. Prelimi­ base system, in general, is comprised of three sub­ nary applications have shown that the system is systems, i.e., information management, information practical and reliable. It opens up a vast range of applications, and information products. These sys­ application prospects for marine resource investi­ tems have played an important role in the insurance gation in China. In the next stage, Chinese schol­ of navigation safety and the exploration of marine ars will continue devoting themselves to the resources (Zhai and Gao, 1996). However, with an improvement of this system in order to raise its increase in the amount and type of marine develop­ stability and reliability further. ment activities, the data base systems of a single factor of hydrographic survey cannot meet the requirements from different users. For the consider­ Suggestions ation of that case, a hydrographic survey data base system in an integrated sense has been recently Mankind has entered the information age. One pays developed successfully in China. Many modern tech­ increasing attention to the applications of geomat- nologies, such as computer technology, network ics and information, which are considered as a part technology, communication technology, data base of the national information network. Many govern­ management technology, graph and image process­ ments across the world are making a huge invest- ment in building their national spatial data infra­ should be considered. It should be encouraged to structure (NSDI) so that every department of gov­ develop modern marine geomatics and informa­ ernment may share its benefit. Digital earth is a tion industry, which is characterised by digital natural prolongation of the information expressway products, and supported by 3S technology. and NSDI plans. Its substance is to express the Earth in terms of a digital, network of intelligent information, and visualisation, using high volume Acknowledgements spatial data of the Earth. Three major tasks are essential to the construction of the digital earth, This research has been supported by the National i.e., data acquisition, data processing, and data Natural Science Foundation of China (No. application. 70% of the Earth surface is covered by 40071070). ocean water, which is an important component of terrestrial space. Therefore, the construction of the digital ocean must be carried out before finishing References the construction of the digital earth. In such a case, a major question that needs to be faced by every Mccaffrey E.K. (1981). A Review of the Bathymet­ government in the near future is to acquire, ric Swath Survey System. International Hydro- process and apply the ocean spatial data. China is graphic Review, LVI I 1(1), 19~27 a developing country. Although, as a result of the effort of many years, great progress has be made Tyce R.C. (1986). Deep Seafloor Mapping Systems in hydrographic surveying technology, it must be - A Review. Marine Technology Society Journal, admitted that the overall level of Chinese hydro- 20(4), 4-16 graphic surveying is far away from that of developed countries. China should pay more attention to the Atanu B., Saxena N.K. (1999). A Review of Shallow following problems in the near future: Water Mapping Systems. Marine Geodesy, 22(3), (1) Survey equipment: the potential applied capac­ 2 4 9 -2 5 7 ity of high and new technology should be con­ sidered to improve the accuracy and reliability Li J B. (1999). Multibeam Survey Technologies and of sounding system. Methods. Ocean Publishing House, Beijing (in Chi­ (2) For data analysis and processing, considera­ nese) tion of the high volume data obtained from new technology means, some key problems, such Chen F.T. (1999). Development of Multibeam as the separation of errors from multi­ Echosounder. Ocean Technique, 18(2), 26-32 (in resources, the fusion of data from multi­ Chinese) resources, the visualisations of graph and image, and the high efficiency transmission of Zhu G.W. (1999). Prospect and Review of Marine data, must be resolved in advance using mod­ Survey During the Last Fifty Years in China. Ocean ern data processing method and computer Technique, 18(3), 1-13 (in Chinese) technology. (3) For the basic infrastructure construction, one Huang M.T., Zhai G.J., Ouyang Y.Z., et al. (2000). should attach importance to the match of spatial Prospect and Development of Multibeam data from ocean and land. A uniform 3D datum Echosounding Technique. Marine Surveying and of ocean and land should be built as soon as Charting, 3, 2-10 (in Chinese) possible. The management of hydrographic sur­ vey data should be considered seriously. Wehr A., Lohr U. (1999). Airborne Laser Scanning— Some work, such as the coordination and dis­ An Introduction and Overview. ISPRS Journal of Pho- tribution system of marine spatial data, the togrammetry and Remote Sensing, 54(2/3), 68-82 web site of data interchange, and the standard of data exchange, etc., should be accom­ Baltsavias E.P. (1999). Airborne Laser Scanning plished as soon as possible. Existing Systems and Firms and Other Resources. (4) For applications and development of information ISPRS Journal of Photogrammetry and Remote products, the importance of maritime GIS system Sensing, 54(2/3),164-198 Andrew A.A., Lloyd C.H., Gerd F.G., et al. (1998). Huang M.T, (1990). Computation and Correction of New Technology for Shallow Water Hydrographic Systematic Errors in Marine Gravity Measurements. Surveys. International Hydrographic Review, 65(2), Journal of Marine Science, 4, 8 1 -86 (in Chinese) 27-41. Huang M.T. (1985). On the Systematic Errors in Tang X. T. (1998). Future Advancements of Airborn Marine Gravity Measurements. Marine Surveying Hydrography in China. Military Surveying and Map­ and Charting, 1, 7 -2 0 (in Chinese) ping, 2, 5 5 -57 (in Chinese) Huang M.T. (1992). Adjustment for Marine Gravity Guan Z., Zhai G.J., Huang M.T., et al. (1999). Survey. Marine Surveying and Charting, 3 ,1 -1 0 (in Development of LADS System. Military Surveying Chinese) and Mapping, 3, 58~61 (in Chinese) Huang M.T. (1993). Marine Gravity Surveying Line Huang M.T., Zhai G.J., Ouyang Y.Z., et al. (2003). System Adjustment. ACTA GEODAETICA et CARTO­ Wave Correction Technique in LADS. Geomatics GRAPHICA SINICA, 2, 103-110 (in Chinese) and Information Science of Wuhan University, 28(4),389-393 (in Chinese) Huang M.T. (1995). Marine Gravity Surveying Line System Adjustment. Journal of Geodesy, 70, Guan Z.H. (1988). Automatic Hydrographic Survey 158-165 System. Tianjin Institute of Hydrographic Surveying and Charting, Tianjin, (in Chinese) Huang M.T., Guan 1., Zhai G.J., et al. (1999a). The Self-calibrating Adjustment of Marine Gravity Sur­ Guan Z.H., Xiao H.T., Li Y.D. (1991). Multi-Func­ vey Network. ACTA GEODAETICA et CARTOGRAPHI­ tional Automatic Hydrographic Survey System. CA SINICA, 2, 162-171 (in Chinese) Marine Surveying and Charting, 2, 15~17 (in Chi­ nese) Huang M.T., Guan 1., Zhai G.J., et al. (1999b). On the Compensation of Systematic Errors in Marine Gravity Zhao X.L. (1998). Development of Automatic Hydro- Measurements. Marine Geodesy, 22, 183-194 graphic Survey System in China. Marine Surveying and Charting, 1, 2 2 -2 6 (in Chinese) Huang M.T., Zhai G.J., Ouyang Y. 1., et al. (2001a). Data Fusion Technique for Single Beam and Multi­ Shen J.S., Wang R., Xie X.J. (1995). Correction of beam Echosoundings (I), The International Hydro- Sound Speed in Hydrography. Marine Surveying graphic BULLETIN, May issue, 12-16 and Charting, 1, 4 7 -5 0 (in Chinese) Huang M.T., Zhai G.J., Ouyang Y. Z.r et al. (2001b). Xie X.J., Zhai G. J., Huang M.T. (1988). Tide cor­ Data Fusion Technique for Single Beam and Multi­ rection Using Time Difference. Marine Surveying beam Echosoundings (II). The International Hydro- and Charting, 3, 2 2 -2 6 (in Chinese) graphic BULLETIN, June issue, 7-11

Liu Y.C. (2000). Mathematical Model for Transfer­ Huang M.T., Zhai G.J., Ouyang Y. Z., et al. (2002a). ring Depth Datum. ACTA GEODAETICA et CARTO- Two-Step Processing for Compensating the Sys­ GRAPHICA SINICA, 29{4), 310-316 (in Chinese) tematic Errors in Marine Gravity measurements. Geomatics and Information Science of Wuhan Uni­ Huang M.T., Zhai G.J., Guan Z,, et al. (1999a). versity, 3, 251-255 (in Chinese) Detection of Abnormal Data in Hydrography. ACTA GEODAETICA et CARTOGRAPHiCA SINICA, 2, Huang M.T., Zhai G.J., Ouyang Y. 1., et al. (2002b). 269-277 (in Chinese) Data Fusion Technique for Multibeam Echosound- ing. Geo-Spatial Information Science, 3, 1 1 -1 8 Huang M.T., Zhai G.J., Guan 1., et al. (1999b). Robust Method for the Detection of Abnormal Data Li D.R. (1988). Error Processing and Reliability The­ in Hydrography. The International Hydrographic ory. Publishing House of Survey and Map, Beijing Review, 2, 9 3-102 (in Chinese) Zhai G.J., Huang M.T., Ouyang Y.Z., et al. (2001). Pre­ Zhai Guojun is Professor of hydrographic surveying. sent State and Future Development of Marine Survey. He works in Tianjin Institute of Hydrographic sur­ Journal of Survey and map, 6, 7~9 (in Chinese) veying and Charting, China. He holds a Ph.D in marine geodesy. Recently, he makes research on Zhai J.S., Gao G.X. (1996). The Development of the airborne laser bathymetry. Hydrographic Data Base in China. Marine Survey­ ing and Charting, 4, 23-28 (in Chinese) Ouyang Yongzhong is Research assistant of marine geodesy. He holds a BSc degree in geo­ desy and now is making research on marine gravi­ Biographies ty surveying.

Huang Motao is Professor of hydrographic survey­ Liu Yanchun is Professor of hydrographic surveying. ing, and Director of the Hydrographic Branch at He holds a Ph.D in marine geodesy. He makes Tianjin Institute of Hydrographic surveying and research on ocean tide analysis. Charting, China. He holds a BSc degree and mas­ ter degree in Geodesy, both from Wuhan Technical Lu Xiuping is Research assistant of hydrographic University of surveying and mapping. He devotes surveying. He holds a BSc degree in hydrography himself in the research on marine gravity survey­ and is now making research on data processing of ing, multibeam echosounding and airborne laser hydrographic surveying. bathymetry. He has presented numerous technical papers covering these fields. E-mail: [email protected]