| The 21st century is the century of ocean development. Deep-ocean survey and operation is one of the most important techniques in ocean development and research field. The widely used deep-ocean observation equipment is ROVs or AUVs-based video surveying system. Underwater video observation is the most straightforward, vivid, and effective short-distance observation method in deep-ocean. The reason is that video images contain abundant details and color information, thus easy to be recognized and understood by human beings. However, how to transmit massive amount of video information acquired by ROVs or AUVs to the surface station is one of the challenges for deep-ocean observation. Therefore, in order to adapt to the limited transmission bandwidth, either for ROVs'tether system or for AUVs' wireless transmission system, massive amount of video and image information must be effectively compressed and encoded prior to transmission. As a result, according to the characteristics of underwater video and acoustic channel, efficient underwater video compression methods have been investigated. The research mainly consists of the following two parts:(1) Research of efficient underwater video coding algorithmAccording to the characteristics of underwater video and observation application, an effective underwater video coding system is successfully developed, which mainly consists of three parts:discrete wavelet transform-based underwater image visual redundancy elimination algorithm, WTWDR-based intra-frame coding algorithm, and dual-WDR coding algorithm of inter frames. Experimental results show that without the influence of channel errors, the proposed compression system can reach the compression ratio from 250:1 to 500:1 for general underwater video images, which can be applied to effective underwater video coding and transmission.(2) Research of error-resilient and efficient underwater video coding algorithmTaking account of the error-prone and limited-bandwidth characteristics of underwater acoustic channels, an efficient and error-resilient underwater video coding system is developed, which is mainly composed of five units, namely, wavelet-based preprocessing unit, inter-frame motion estimation and compensation unit, data partition and packetization unit, and error detection and concealment unit at the decoder. Experimental results show that the proposed algorithm can tolerant packet loss rate less than 20%, bit error rate less than 0.001, and burst error rate less than 0.002. In addition, the algorithm can achieve compression ratio from 170:1 to 370:1. Hence, the developed underwater video coding algorithm can be applied to rapid underwater video transmission via underwater acoustic channels. |
PDF Full Text Request