Data Recording And Replaying Of VTS Radar And VFH Signals

The recording and replaying unit in VTS (Vessel Traffic Services) mainly completes the function that can record multi-information data such as radar raw video, plotting, VHF audio. It can also replay part of the record data. Since there is a maritime accident, it is necessary to replay the radar raw video and VHF call audio. Because of the time consistency of radar raw video and the VHF audio data, there always be a requirement of synchronously replaying in the given period of time.This subject comes from the LiaoNing Provincial Foreign Experts Bureau project (LiaoNing Foreign Experts letter [2012]26):Developing of VTS based on the solid-state radar. The paper studies the recording and replaying of radar raw video and VHF audio.In radar raw data recording process, analyses the Zlib compression method and file structure of radar video; In VHF audio recording process, focuses on PCM-based acquisition and compression of VHF audio, and then the WAVE file structure. According to the recording process, further studies file extraction mechanism of integration and synchronization mechanisms of the replaying process. In the last, realizes the synchronously replaying of radar raw video and VHF audio by Visual Studio2010programming project, finally verifies the project feasibility applied to the VTS development. The paper is mainly divided into three parts.The first part includes the1st,2nd and3rd chapters. Basically studies the data recording process. In radar data recording section, the Zlib library functions achieve lossless radar data compression by a combination of LZ77and Huffman compression theory. The Radar file structure has a index head unit, while radar frame data shows data length and time information, which makes radar file download and replay smoothly. In VHF data recording section, VHF audio is recorded in the format of WAVE file header and data block which lays an important foundation for the interception and splicing of audio replaying,The second part based on the4th chapter, studies data replaying. Radar video data uses the index unit to extract the required time period file; the VHF audio data can achieve file interception and stitching according to its format. Finally, radar and VHF data can achieve synchronously replaying by using the timestamp of the file headers. Begining time differs within3seconds, so the waiting synchronization mechanism is practicable. The third part is corresponding to the5th chapter, it achives data replaying by programming in Visual Studio2010. The use of multi-threads can control the radar video and VHF audio synchronously replaying. Radar video replaying module and VHF audio replaying module is constructed by different thread. Then the synchronization thread controls data synchronization by time information. This paper verifies the feasibility of the two data synchronously replaying.