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Underwater passive navigation technology is one of the important development orientations in the field of modern
navigation. With the advantage of high self-determination, stealth at sea, anti-jamming and high precision, passive
navigation is completely meet with actual navigation requirements. Therefore passive navigation has become a specific
navigating method for underwater vehicles. The scientists and researchers in the navigating field paid more attention to
it. The underwater passive navigation can provide accurate navigation information with main Inertial Navigation System
(INS) for a long period, such as location and speed. Along with the development of micro-electronics technology, the
navigation of AUV is given priority to INS assisted with other navigation methods, such as terrain matching navigation.
It can provide navigation ability for a long period, correct the errors of INS and make AUV not emerge from the seabed
termly. With terrain matching navigation technique, in the assistance of digital charts and ocean geographical
characteristics sensors, we carry through underwater image matching assistant navigation to obtain the higher location
precision, therefore it is content with the requirement of underwater, long-term, high precision and all-weather of the
navigation system for Autonomous Underwater Vehicles.
Tertian-assistant navigation (TAN) is directly dependent on the image information (map information) in the navigating
field to assist the primary navigation system according to the path appointed in advance. In TAN, a factor coordinative
important with the system operation is precision and practicability of the storable images and the database which produce
the image data. If the data used for characteristics are not suitable, the system navigation precision will be low.
Comparing with terrain matching assistant navigation system, image matching navigation system is a kind of high
precision and low cost assistant navigation system, and its matching precision directly influences the final precision of
integrated navigation system. Image matching assistant navigation is spatially matching and aiming at two underwater
scenery images coming from two different sensors matriculating of the same scenery in order to confirm the relative
displacement of the two images. In this way, we can obtain the vehicle's location in fiducial image known geographical
relation, and the precise location information given from image matching location is transmitted to INS to eliminate its
location error and greatly enhance the navigation precision of vehicle.
Digital image data analysis and processing of image matching in underwater passive navigation is important. In regard
to underwater geographic data analysis, we focus on the acquirement, disposal, analysis, expression and measurement of
database information. These analysis items structure one of the important contents of underwater terrain matching and
are propitious to know the seabed terrain configuration of navigation areas so that the best advantageous seabed terrain
district and dependable navigation algorithm can be selected. In this way, we can improve the precision and reliability of
terrain assistant navigation system. The pre-process and format transformation of digital image during underwater image
matching are expatiated in this paper. The information of the terrain status in navigation areas need further study to
provide the reliable data terrain characteristic and underwater overcast for navigation. Through realizing the choice of
sea route, danger district prediction and navigating algorithm analysis, TAN can obtain more high location precision and
probability, hence provide technological support for image matching of underwater passive navigation.
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