Publication: Development of a 2d underwater acoustic based localization system
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Date
2012-06-01
Authors
Chew, Shu Yang
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Abstract
Underwater localization is widely used in military, marine, research and surveillance activities. To localize or position an object in underwater, one has to be able to sense and acquire distance information in underwater environment. The challenges are sensing in underwater environment is different from normal sensing in open air environment. Methods that work for normal sensing do not work in underwater. The project focuses are development of mathematic model for underwater acoustic based localization system, design and fabrication of underwater sensor and the investigation of acoustical relationship between variables for acoustic wave. Underwater sensor has to be able to detect and determine distance from of target of interest. Hydrophone is the underwater sensor in this particular project. It can work as both transmitter and receiver for acoustic signal. Acoustic sensing is implemented in underwater localization. Strength of signal is proposed to be the method to determine the relative distances between target and sensor network. By comparing the signal intensities between different nodes, the position of a target of interest can be localized using positioning technique. Mathematical model is constructed based on the inverse square relationship model between intensity of signal and distance and the result can be displayed visually to user. Experiments in four different actual environments are done after modelling to verify the inverse square relationship model. The result proven that the relationship between signal intensity and distance in swimming pool is the closest to theoretical relationship applied in model and it fits the inverse square model with a correlation coefficient of 0.902604. The experimental relationships obtained are different from ideal inverse square relationship. Factors like absorption and reflection affect the signal intensity other than propagation loss. Types of acoustic transducers and different testing environment also affect the quality of received signal in term of reflections. Transducer with high directionality is immune to the effect of reflections. And on the other hand, background noise, originating from wall reflections is found to be increasing with the decrease of water body where the testing been carried out in.