GPS广播星历与历书的精度比较

Precision Comparison between GPS Broadcast Ephemeris and Almanac

GPS接收机接收到广播星历与历书两种导航信息，广播星历包含基本轨道参数及摄动改正量，由其确定的卫星位置精度高，可用于定位计算。历书仅提供基本轨道参数，精度低，可用于接收机快速捕捉卫星和预报。文章利用实际的广播星历和历书数据，进行轨道计算，并与IGS提供的精密星历进行了比较，结果表明广播星历在有效期内算得卫星位置的精度为米级，推算12小时后，精度迅速降至几百米，而使用历书算得卫星坐标，一天内的精度为1～2km里，推算6天其精度仍在2km以内，推算10天也可保持公里级精度。

GPS receiver can receive two kinds of ephemeris, i. e. broadcast ephemeris and almanac. The former, including basic Doppler parameters and disturbance errors, can determine the satellite position in high precision, therefore, it can be used for real-time positioning. While the latter only contains basic Doppler parameters and the precision of position determination is rather lower. Generally, almanac is used for GPS receiver to track satellite signal and for the ephemeris forecast. In this paper, the both have been used to calculate satellite position in different time spans. Analysis shows that compared with precise ephemeris provided by IGS （Intemational GPS Service）, the position precision solved by broadcast ephemeris is several meters in the following 2 hours since the reference epoch, and it reaches 300 meters after 12 hours. As for almanac, the precision is better than 2km, which can last for ten days.