Research On Radar Lmage Compression Technology And Its Test System For Shipborne Voyage Data Recorder (VDR)

With the rapid development of scientific technology, new marine digital aids, such as ECDIS(Electronic Chart Display and Information System), AIS(Automatic Identification System) and VDR(Voyage Data Recorder), have being installed and applied on board at present, this implys that the ship's navigation at sea has gradually stepped into the epoch of "marine digital transport ". VDR, as one of connotations of the future "marine digital transport", is a marine aid for recording the ship navigational data in real-time, which can be downloaded and replayed with special appliance or sofeware These data are very importantly helpful and meaningful to analyze the marine accident and determine the responsibility when the ship accident was occurred. It is well kowned that the sea state and situation are complicated and changeable when the ship proceeds at sea so that a large number of ship's data are needed to be stored. Hence, on the premise of the quality of playback data, how to effectively compress the navigational data during the process of the data storage and transmission in order to save the storage volume is the most essential issue to be solved for developing and researching VDR.According to the research on the storage volume of navigational data in VDR products, the disk volume is mainly occupied by the video data, shipborne radar image and the audio data, bridge communication. So, these two kinds of data are the "bottle-neck" to improve effectively storage volume in VDR. Because most VDR products adopted the DCT(Discrete Cosine Transform) method or hardware technology to compress the radar image currently, this dissertation has maken new research and presentation to the shipborne radar image compressionand playback technology for VDR in detailDuring the rsearch, as per the successful application in image compression with wavelet transform nowadays, the compression algorithm based on EZW(Embedd Zerotree Wavelets coding) and arithmetic codec for shipborne radar image in VDR is presented. And this dissertation also has given the research of the wavelet transform theory, the basic principle of EZW and arithmetic codec in detail.One of the obvious differences between the wavelet transform and Fourier transform is that the wavelet function is not unique in wavelet transform. Different wavelet base produced by the different wavelet function has different time-frequency characteristics, and analyzing the same issue with different base will lead to the different result. Thereby, the choice of wavelet function in the application to research practical issue is one of the critical questions firstly. This dissertation, in accordance with lots of research materials, has summarized the effect of the characteristics of orthogonality, compactly supported, symmetry, regularity and vanishing moment etc., to image compression performance, and selected 9 wavelet functions which are usually used in image compression and a representative shipborne radar image, and respectively tested, analyzed and compared the compression ratio and PSNR(Peak-Signal-Noise Ratio) through the EZW image compression system developed in this dissertation. The final conclusion of the biorthogonal spine wavelet function, Bior3/9, adopted by this dissertation has been drawn.Currently, the VDR manufacturers mostly respectively implement the test for radar image compression technology in VDR through the hardware devices developed by them, so it is hard to compare the test result each other. This dissertation, in compliance with the relevant requirements of "Test Guidance for Shipborne Voyage Data Recorder" issued by the CCS(China Classification Society), has developed the software of "Test System for Radar Image Compression Technology in VDR" and test the EZW algorithm adopted in this dissertation. The analytical and tested data have indicated that the EZW is not only[Vsuitable for the radar image compression in VDR, but also can get the reasonable storage volume in addition, the Test System developed in this dissertation can also provide a common...