Delay analysis of two way time transfer based on troposphere gradients

It analyzed three troposphere mapping functions, Niell Mapping Function (NMF), Vienna Mapping Function 1 (VMF1) and Global Mapping Function (GMF), and its parameters selection and characteristics paralleled. Also it presented the thumb rule in troposphere mapping function and designed a two way time transfer method based on troposphere mapping functions. Besides it studied the station height errors based on troposphere gradients. It analyzed the above methods in four GPS stations in mid latitude northeast Asian areas. It could conclude from the studies that the station height errors distribute in cosine distribution with a yearly period and the maximum and minimum display in ad-jacency of summer & autumn and winter & spring. The chosen stations´ height errors are in mm precision. And the station height errors increase with the two way transfer distance´s length.