Current situation and prospect of deep-sea ultra-short baseline positioning system
Underwater acoustic positioning technology has stable and high-precision positioning ability, and can directly provide absolute position information for various deep-sea exploration equipment. The acoustic transducer array of the ultra-short baseline positioning system is installed on the bottom of the ship, which is convenient for large-scale maneuvering operations, and has become an indispensable underwater acoustic positioning equipment for modern oceanographic research ships. This paper first introduces the basic principle of ultra-short baseline positioning, and then systematically introduces the deep-sea long-range ultra-short baseline positioning systems of iXblue of France, Kongsberg of Norway, Sonardyne of Britain, LinkQuest of the United States, Evologics of Germany and other companies. Taking the remote ultra-short baseline positioning system of Harbin Engineering University as an example, the domestic development situation is analyzed, and the development trend of the deep-sea remote ultra-short baseline positioning system is forecasted.
1 Introduction
Submersibles are essential carrying equipment for deep sea scientific research and investigation operations [1-4]. The underwater positioning of submersibles is an important problem that can not be ignored in the deep-sea resource investigation and scientific research by using all kinds of submersibles, and the medium environment of the ocean determines that sound is more suitable than light and electromagnetic wave as the transmission carrier of underwater positioning technology. According to the receiving array base line length classification, underwater acoustic positioning technology can be divided into long base line positioning system, short base line positioning system and ultra-short base line positioning system [5~6]. The ultra-short baseline positioning system [7~8] converts the relative position measured by the on-board acoustic transducer array to the geodetic coordinate system through the global positioning System (GPS) and attitude sensor to obtain the geodetic latitude and longitude coordinates of the submersior. The ultra-short baseline positioning system has the advantages of simple composition, convenient operation and large-scale maneuvering operation. It can provide technical support for various high-precision operations such as underwater target positioning and tracking and underwater remote control operation, making it play an increasingly important role in the field of Marine resources investigation and scientific research.
This paper first introduces the basic principle of ultra-short baseline positioning, and then systematically introduces six typical deep-sea long-range ultra-short baseline positioning systems from iXblue (France), Kongsberg (Norway), So⁃nardyne (UK), LinkQuest (US) and Evologics (Germany). Taking the remote ultra-short baseline positioning system of Harbin Engineering University as an example, the domestic development situation is analyzed, and the development trend of the deep-sea remote ultra-short baseline positioning system is forecasted.
2 Ultra short baseline positioning system
2.1 Basic Principles
According to the different operating frequency and operating distance, the array length of the ultra-short baseline positioning system is generally ranging from a few centimeters to tens of centimeters. The ultra-short baseline positioning system has two ways of working: one is the acoustic response mode, the water surface sends an inquiry signal to each transponder, and each transponder sends an inquiry signal after receiving its own inquiry signal, and calculates the distance by calculating the time difference between sending an inquiry signal and receiving a response signal. The other is the synchronous clock trigger mode, if there is a cable, the trigger pulse triggers the transponder through the cable, if there is no cable, it needs to use a high-precision synchronous clock to synchronize the trigger transponder and the water surface system, and calculate the distance by calculating the time difference between the synchronization pulse trigger time and the receipt of the response signal.
It is necessary to know the sound velocity to calculate the distance from the time difference, so accurate sound velocity profile data is the guarantee of positioning accuracy. Therefore, at each new location, the sound velocity profile must be measured and entered into the positioning system. If there is a severe meteorological process (such as strong winds, heavy rain), the sound velocity profile needs to be re-measured and updated into the positioning system. In order to determine the underwater position of the submersible, in addition to measuring the distance, it is necessary to measure the Angle of direction and the Angle of inclination. The direction Angle and inclination Angle of the ultra-short baseline positioning system are calculated by analyzing the phase difference of the received signal of the acoustic transducer array on board. The combination of surface-borne GPS and ultra-short baseline positioning system can accurately determine the precise position of the underwater transponder.
2.2 System Composition
The ultra-short baseline positioning system consists of surface Marine equipment and submersible transponders. Surface Marine equipment includes signal processing units, an array of onboard acoustic transducers, and peripheral auxiliary sensors such as GPS and attitude sensors. The shipborne acoustic transducer array is mounted on the bottom or side of the ship and consists of a transmitting transducer in the center and a plurality of hydrophones on all sides. The underwater part mainly refers to the transponder, and if it works in synchronous clock trigger mode, it also needs to include synchronous clock. Usually, the ultra-short baseline transponder is installed on the back of the underwater carrier, and its hemispherical directivity can cover the entire upper half of the space, ensuring that the ultra-short baseline positioning system can work normally under various underwater depths and inclination states.
2.3 Operating Frequency Band
The selection of the working frequency band of the ultra-short baseline positioning system depends on two points: positioning accuracy and maximum operating distance [9]. Table 1 shows the correspondence between the operating frequency band and the maximum operating distance.
The deep-sea remote ultra-short baseline positioning system usually selects the low or medium frequency band, and the ultra-short baseline positioning system for the whole sea depth generally selects the low frequency (8kHz~16kHz), or lower frequency band.
3. Development status of deep-sea long-range ultra-short baseline positioning system
At present, the foreign ultra short baseline positioning technology is relatively mature, and the ultra short baseline positioning system has been productized, industrialized and serialized. The main international manufacturers of ultra-short baseline positioning system are: iXblue in France, Kongsberg in Norway, Sonardyne in the United Kingdom, LinkQuest in the United States, Evologics in Germany and other companies. Table 2 gives a comparison of typical remote ultra-short baseline positioning systems abroad.
POSIDONIA II from iXblue, France
iXblue, a French company, began to develop a new generation of long-range ultra-short baseline positioning system in 2000, and finalized the product in 2010, named POSIDONIA II [10]. The maximum positioning depth of POSIDONIA II can reach 7000 m, and the maximum positioning tilt distance can reach 8000 m~10000 m. Thanks to iXblue's strong technical foundation and complete research and development team, POSIDONIA II's biggest feature is strong combination compatibility and unique data fusion technology. Performance is optimized when combined with the company's other navigation devices, such as OCTANS motion sensors and PHINS INS. In addition, POSIDONIA II can be combined with the RAMSES 6000 long baseline and PHINS inertial navigation to form a complete modular underwater navigation system, providing robust, high-update positioning information.
According to the different installation methods of the ship bottom, the acoustic transducer array of POSIDONIA II can be divided into two types. One is vertically reportable. The transducer array can be lowered to the ship bottom 1.5m through the vertical lifting mechanism to further avoid the interference of the ship noise, and its transducer size and weight are small. The other is the flush installation type, the acoustic transducer array is fixed together with the bottom of the ship, the size and weight of the transducer is larger, and the corresponding emission sound source level is higher.
4 Development trend of deep-sea long-range ultra-short baselines
By comparing and analyzing typical remote ultra-short baseline positioning systems at home and abroad, and referring to some other systems, the development trend of deep-sea remote ultra-short baseline positioning systems can be obtained.
4.1 Combination of ultra-short baseline and long baseline
The disadvantage of the ultra-short baseline positioning system is that the positioning accuracy is related to distance/depth. In the field of deep sea operations support, some operations require more accurate positioning, which requires long baseline positioning systems. The advantage of the long baseline positioning system is that the positioning accuracy is high, and it is independent of the depth, and the disadvantage is that the beacon array needs to be placed, and the equipment and time cost are high. If the long baseline positioning system is combined with the ultra-short baseline positioning system, the long/ultra-short baseline combination positioning system is developed, which can not only ensure the positioning accuracy independent of the working water depth, but also have the characteristics of ultra-short baseline mobility and flexibility, so as to achieve continuous high-precision navigation and positioning of underwater carriers. In this regard, the British company Sonardyne is a pioneer, they have launched LUSBL combined positioning system.
4.2 Integration of ultra-short baseline and attitude sensor
The separate installation of the measuring equipment in the ultra-short baseline leads to the inevitable installation deviation between the acoustic transducer array and the peripheral auxiliary sensor. Although the deviation can be corrected effectively through the calibration test at sea, new deviation will be introduced over time, resulting in the deterioration of positioning performance. Each correction needs to choose the right sea area, and consumes a lot of time, manpower and material resources. If the attitude sensor and acoustic transducer array are integrated and calibrated in the laboratory, the development of portable, plug and play, calibration free ultra-short baseline positioning system is undoubtedly the future development trend. In this regard, the French company iXblue is a pioneer, and their GAPS ultra-short baseline positioning system is widely welcomed.
4.3 Combination of ultra-short baseline and high-speed digital underwater acoustic communication
The ultra-short baseline positioning system can locate and track underwater targets. Digital underwater acoustic communication is the primary technical means of underwater wireless information acquisition, transmission and control. Most oceanographic survey equipment requires digital underwater acoustic communication for data transmission, or command interaction. If the ultra-short baseline and high-speed digital underwater acoustic communication can be combined, the communication function can be added to the ultra-short baseline, or the positioning function can be added to the digital communication system, and the underwater integrated communication positioning system without positioning and communication mode conversion can be developed to realize the synchronous calculation of positioning data during the acoustic communication transmission. In this regard, Evologics of Germany and Sonardyne of the UK are the first to introduce ultra-short baseline positioning systems with high-speed digital underwater acoustic communication capabilities.
4.4 Higher update rate of location data
When the acoustic response mode is used, the ultra-short baseline is usually after the previous response signal is received before the next inquiry can be conducted. When the synchronous trigger mode is used, only one-way sound propagation is required, and the data update rate can be doubled. However, in deep-sea integrated applications, no matter what kind of working mode, its positioning data update rate is relatively low. If the positioning pulse is encoded, the ultra-short baseline positioning system can correctly decode the received response signal and determine its corresponding positioning round, then it can continuously send multiple inquiry pulses to the transponder before the last response signal is received, which can greatly improve the positioning data update rate of the ultra-short baseline positioning system. In this regard, the UK company Sonar⁃dyne is a pioneer, with their ultra-short baselines that achieve up to 1s update rate in any water depth environment.
5 Conclusion
With the continuous improvement of deep-sea development technology, people have adopted more and more research means, such as manned submersible, ROV, AUV, underwater glider, deep towing system, TV grab and other detection equipment. The ultra-short baseline in underwater acoustic positioning technology has the advantages that other navigation and positioning systems do not have. It can directly provide absolute position information for all kinds of detection equipment, and become an essential positioning means in deep sea exploration.
Although there are many companies and research institutes in the world that can provide mature serialized ultra-short baseline positioning systems, with the continuous progress of science and technology, human beings have put forward higher and higher requirements for deep-sea underwater positioning technology. Based on the comparison and analysis of typical deep-sea remote ultra-short baseline positioning systems at home and abroad, combined with the actual needs of deep-sea survey, it can be concluded that the development trend of deep-sea remote ultra-short baseline positioning systems is as follows: 1) the combination of ultra-short baseline and long baseline; 2) Integration of ultra-short baseline and attitude sensor; 3) Combination of ultra-short baseline and high-speed digital underwater acoustic communication; 4) Higher positioning data update rate.
reference
[1] Feng Xisheng, Liu Yongkuan. Current situation and trend of autonomous underwater vehicle research and development [J]. High-tech Communications, 1999,9 (9) : 55-59. (in Chinese)
[2] Li Yiping, Li Shuo, Zhang Aiqun. Research status of autonomous/remote-controlled underwater vehicle [J]. Engineering Research-Engineering from Interdisciplinary Perspective, 2016, 8 (2) : 217-222. (in Chinese)
[3] Feng Xisheng, Li Yiping. 30 years of Marine robots [J]. Chinese Science Bulletin, 2013,58 (Supplement II) : 2-7.
[4] Li Ye, Chang Wentian, Sun Yushan, et al. Research status and Prospect of autonomous Underwater Vehicle [J]. Robot Technology and Application, 2007,14 (1) : 25-31. (in Chinese)
[5] Sun Dajun, Cheng Cui-e. Discussion on development trend of underwater acoustic navigation and positioning technology [J]. Journal of Marine Technology, 2015,34 (3) : 64-68. (in Chinese)
[6] Li Shoujun, Bao Gengsheng, Wu Shuigen. The development status and prospect of underwater acoustic positioning technology [J]. Marine Technology, 2005,24 (1) : 130-135. (in Chinese)
[7] Zhu Min, Zhang Tongwei, Yang Bo, et al. Jiaolong manned submersible acoustic system
[J]. Chinese Science Bulletin, 2014,59 (35) : 3462-3470.
[8] Zhang Tongwei, Liu Yeyao, Yang Bo, et al. Underwater acoustic active positioning technology and its application on manned submersible [J]. Journal of Marine Technology, 2016, 35 (2) : 56-59. (in Chinese)
[9] Vickery K. Acoustic positioning systems: A practical over⁃view of current systems [C] //Workshop on Autonomous Underwater Vehicles, 1998. 5-17.
[10] http://www.ixblue.com/ [EB/OL].
[11] https:// www.km.kongsberg.com/ [EB/OL].
[12] https:// www.sonardyne.com/ [EB/OL].
[13] http://www.link-quest.com/ [EB/OL].
[14] https:// www.evologics.de/ [EB/OL].
