Simulation analysis of differential phase delay estimation by same beam VLBI method

Abstract

The same beam VLBI method (SBV) is newly applied to the multi-frequency VLBI method in the VRAD mission of SELENE (KAGUYA). By simultaneously observing two nearby spacecraft with one antenna, the error sources of VLBI measurement common in two propagation paths can be almost canceled out. In this paper, error estimation and simulation analysis are carried out for a feasibility study to apply the SBV method to the VRAD mission. Differential phase delay can be estimated without cycle ambiguity even if tropospheric fluctuation is large and/or traveling ionospheric disturbance occurs. The sensitivity of the differential phase delay with respect to the average elevation angle and the elongation of two spacecraft is also investigated. Moreover, a method is developed for estimating differential phase delay in switching VLBI observations using the cycle ambiguity derived from SBV observations. This method can be performed in more than 90% of the VRAD mission's total paths. Precise positioning with SBV contributes to accurate estimation of the low degree coefficients of lunar gravity fields by more than one order of magnitude than previous results.

Differential Phase Delay Estimation in VRAD Mission of SELENE (KAGUYA)

“…By alternately observing R/Vstar with a switching interval of Tsw, the tropospheric and the ionospheric fluctuations whose period is shorter than Tsw can be canceled out. The other method is the same-beam VLBI observation method 5,8) . With this method, when the elongation is smaller than the beam width of the ground antenna, the middle point of R/Vstar is tracked and its signals can be simultaneously received.…”

“…This result confirms that the desired accuracy of VRAD, which is 3.3 ps in a 110-second integration interval, can be achieved 2) . However, the same-beam VLBI observation period accounts for about 60% of the total observation period in VRAD 5) . In order to estimate the lunar gravity field at the level of accuracy desired for VRAD, the DPD in the switching VLBI observation period is an important factor.…”

“…In order to estimate the lunar gravity field at the level of accuracy desired for VRAD, the DPD in the switching VLBI observation period is an important factor. Although it is difficult to estimate the DPD under cloudy conditions and/or when traveling ionospheric disturbance occurs in the ionosphere above the VLBI station 5) , there are cases in which the DPD can be successfully estimated. This paper describes the method we used to estimate the DPD during the switching VLBI observation period and shows the results we obtained.…”

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

“…We refer to this as the multi-frequency VLBI method. The conditions which enable the multi-frequency VLBI method to be successfully implemented have been investigated by Kono et al (2003) and Kikuchi et al (2008). The maximum error in the group delay which still allows the cycle ambiguity of S8 to be resolved, is 83 ns.…”

“…This paper describes the scientific objectives, on-board mission instruments, ground stations, mission schedule, performance tests, data products and preliminary results obtained by the gravimetric observations by VLBI in SELENE. New technical developments, such as the multi-frequency VLBI method (Kono et al 2003), the same-beam VLBI method (Liu et al 2007a; Kikuchi et al 2008), and a new method of measuring the phase characteristics of an antenna , which have been established to enable a more precise orbital determination, are also introduced.…”