Research On Active Detection To Underwater Targets Based On Time Reversal Technique

The Time Reversal technology is a novel adaptive channel matched technology. It can focuse most of its energy on specified targets even in the inhomogeneous waveguide environment. This article explores how time reversal(TR) can be used in locating targets in highly cluttered environments. When the time reversal mirror receives a signal, it retransmits the time dispersed signal back to the channel. This process can adaptively match the unknown channel and eliminate the impact of inhomogeneous medium on communication. The more inhomogeneous the media is, the higher the focusing effect is achieved. So, it can enhance the anti-interference ability and effectively eliminate the Multipath Effects of underwater acoustic channel By using the time reversal focusing characteristic, we can effectively overcome the heterogeneity and variability of underwater acoustic channel to improve the communication rate and extend communication distance.This article systematically and thoroughly discusses time reversal theory. Also it introduces the background knowledge of time reversal application. That is the basic knowledge of underwater acoustic channel, such as the KRAKEN Normal Mode. This article mainly discusses how to realize active detection of underwater targets using time reversal Technique.The major work and innovation are as follows:1. Summarizes origin and development of the time reversal theory. And derives the focusing principle of the time reversal. Briefly introduces the application and development of time reversal.2. Introduces the relevant theory of time reversal. Mainly focuses on the underwater acoustic channel mode. Describes the KRAKEN Normal Mode in detail.3. Then discusses four methods of active detection based on time reversal technique: TR(time reversal), Repeated time reversal iteration, DORT and MUSIC.TR uses the focusing property to detect underwater target. Repeated time reversal iteration can correct deviations by iteration and can achieve better positioning effect to underwater targets. DORT and MUSIC algorithm are arrived by analyzing the convergence of the time reversal operator which are easier and can achieve better positioning performance.4. Reference to Radar detection, this article develops a new algorithm named TRAIC (the time reversal adaptive interference canceler)- TRBF (time reversal beamformer) to detect and locate targets in underwater environments. It utilizes time reversal in two stages: 1)Anti-focusing(TRAIC): time reverses and then reshapes the clutter backscatter to mitigate the clutter response; 2)Focusing(TRBF): time reverses the residua backscatter to focus the image on the target.5. Simulates five methods in underwater detection mentioned above. And compares the advantage and disadvantage of each method...