Estimating Tropospheric Slant Scatter Delay at Low Elevation
CHEN Xihong① LIU Zan① LIU Jiye① LIU Jin① ZHANG Qun②
①(Air and Missile Defense College, Air Force Engineering University, Xi’an 710051, China) ②(Information and Navigation College, Air Force Engineering University, Xi’an 710077, China)
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.
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