Development Of Temperature Humidity And Pressure Measuring Instrument Used In The Tropospheric Delay

In order to support the system time compatibility and interoperability of Beidou navigation system for adapting to the international development, Chinese Academy of Sciences, National Time Service Center established a GNSS system time offset monitoring platform. The platform used space-based signal receiving to monitor the time offset. The accuracy of the monitoring system was 5.0 ns.According to the error sources of the system time offset monitoring, this paper analyses how the temperature and humidity and pressure affect the tropospheric delay. The time offset monitoring system used the simple tropospheric model which was only related to the satellite elevation because of the lack of meteorological parameters acquisition. A method which uses the real-time meteorological data to improve the accuracy of the tropospheric delay correction is given. A temperature humidity and pressure measuring instrument which is suitable for the navigation receiver is developed. By using the developed measurement instrument, the acquired data will be used to calculate the tropospheric delay via current common troposphere models. The main contents of the paper include the following aspects:1. Analysis of the influence of tropospheric delay in the GNSS system time offset monitoring, the real-time temperature and humidity and pressure are required tropospheric delay algorithm. The specific design requirements are given for the development of the measuring instrument.2. Using FPGA chip as the core processor, the temperature and humidity and pressure measuring instrument has been designed and implemented. The instrument can communicate with navigation receiver via RS232 serial port. Communication data format is standard NMEA format. The measurement data can be recognized and used by the navigation receiver directly. The temperature error is less than 0.5℃,humidity error is less than 5%, pressure error is less than 10 h Pa. The minimum period for data output is 10 s.3. The developed measuring instrument has been used with GNSS multi-mode navigation receiver to acquire the real-time metrological data of Lintong station.With the collected data, the common tropospheric delay models such as Marini,Hopfield, Saastamoinen and Black are compared and analyzed. The scope and conditions of each model are given.Continuous and stable operation of the temperature humidity and pressure measuring instrument with time offset monitoring receiver has been achieved over72 hours. The tropospheric delay error can be controlled at the decimeter level. Thus the tropospheric delay error has been effectively improved. This method to reduce the tropospheric delay error can be used in other direction such as precise positioning,time transfer and so on.