Method of Calculating VLBI Phase Delay Based on DOR Signal of a Satellite

In deep space exploration,the VLBI technique is a precise method for the angular measurement,which can give the plane-of-sky position information.The group delay of DOR signal can usually be obtained with an accuracy of nanosecond in the VLBI observation.The accuracy of group delay can bring an orbital error of lunar probe about a hundred meters for a baseline of about 2000 kilometers.Especially in the further deep space exploration,the orbital error will be much larger.A method to calculate the small biased phase delay of VLBI is proposed in this paper in order to improve the accuracy of the orbit and position determination.The small biased phase delay is acquired by using the phase delay with ambiguity approaching the middle of bandwidth synthesis group delay of DOR signal.The method both in continuous and discontinuous observation is feasible, proved by processing the data from CE-2 satellite A DOR experiments.The relationship between the group delay and phase delay is discussed.Both of the closure group delay and the closure phase delay of three baselines of SH-BJ,SH-UR and BJ-UR are calculated,and the errors of them are analyzed.The phases of the carrier and the DOR tones are compared to prove the validity of the method.The phase delay's error,especially the random error, can be reduced.The system error will be acquired hopefully during the further processing of orbital determination.