星载AIS报文时间解析

Decoding analysis of time information from space-based AIS message

星载船舶自动识别系统(Automatic Identification System,AIS)接收到的报文中解析出发送报文的时间信息能够有效提高AIS报文在全球海上目标监控等方面的应用价值。着眼于动态显示某一特定船舶进行连续跟踪这一目的,结合天拓一号AIS和天拓三号AIS来研究报文中的时间信息。首先,利用天拓一号星载AIS在轨运行期间接收到的所有数据进行统计分析。通过统计分析发现仅仅依靠报文自身的自组织时分多址(Self-Organizing Time Division Multiple Access,SOTDMA)通信状态等信息不能有效解析报文时间。其次,研究了天拓三号AIS的报文组成格式。通过每间隔1min往星上存储器中植入一个时间信标的方式,天拓三号AIS系统很好地解决了问题,实现了对每一条报文的精确时间显示,为今后实现海面船舶进行连续跟踪与监视提供了良好的技术基础。

The time information evaluated from the message of the automatic identifying system（AIS）is of most importance in monitoring and controlling of the global vessels.Aiming at continuously monitoring some particular vessels,the time information in the AIS messages of the AIS systems onboard both the TianTuo-1（TT1）and TianTuo-3（TT3）micronano satellites was studied.Firstly,a statistical analysis was performed by employing the AIS data received by the TianTuo-1 nano-satellite during its on-orbit operation.The results suggest that it is impossible to obtain the time information merely by the AIS message itself.Secondly,the composition and format of the AIS message received by the TT3-AIS was studied.In the TT3-AIS system,a time-flag was generated every minute to be inserted into the received AIS data package.Thus the TT3-AIS has a good function on adding the time information to the AIS messages,which will be helpful for monitoring and controlling of the global vessels.