低仰角下对流层散射斜延迟估计方法

Estimating Tropospheric Slant Scatter Delay at Low Elevation

对流层斜延迟是对流层散射双向时间比对系统的主要误差来源,目前尚未有对系统中对流层斜延迟进行精确估计的模型。为精确估计斜延迟,引入电磁波射线描迹法,并利用Hopfield天顶延迟模型中折射率计算方案改进描迹法,以克服该方法对探空数据的依赖。首先,根据北纬35？~37？范围内的3个测站2010~2012年的实测气象数据和天顶延迟数据,验证Hopfield模型精度范围小于35 mm;然后,将3个测站按相互基线距离的不同分为3组比对站,利用改进后的模型结合2012年的气象数据,计算了在0？~5？入射角下,一年的斜延迟,并得出最大斜延迟对应的年积日和入射角。计算结果表明,3组比对站的最大单向斜延迟为24.94~45.37 m。在双向比对抵消90%的情况下,时间延迟为3.1~5.7 ns;相互抵消95%时,时间延迟为1.5~2.9 ns。

Troposphere slant delay is the main error source in two way troposphere time transfer. But there is not an accurate model to estimate the slant delay caused by tropospheric in this system. In order to estimate accurately slant delay, the method of ray tracing is presented. Computing mode of refractive index in Hopfield model is introduced to overcome the method＇s dependence on radiosonde data. Meteorologic data of three observation stations of 35 ？ to 37 ？ N in 2010~2012 are selected to improve the applicability of the Hopfield model, the results suggest that precision is less than 35 mm. Then, in order to calculate the tropospheric delay under different angle of incidence（0 ？ ~ 5 ？） through modified model, three parts observation stations are distinguished by different length, modified model is used to estimate to slant delay of those parts. In the process, meteorologic data of those stations in 2012 is selected. The results suggest that max delay is 24.94~45.37 m in a single way. In two way time transfer, when the delay can counteract 90% or 95%, time delay is 3.1~5.7 ns or 1.5~2.9 ns.