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

Abstract

In the very long baseline interferometry (VLBI) radio sources mission of selenological and engineering explorer, the differential phase delay between the Rstar and Vstar sub-satellites is obtained by using the multifrequency VLBI method during the switching VLBI observation period. The cycle ambiguity is successfully determined and the differential phase delay is estimated within an error of 7 picoseconds. The RMS error is somewhat larger than that for the case of same-beam VLBI because fluctuations of propagation delays whose periods are shorter than the switching interval cannot be canceled out between Rstar and Vstar. However, the differential phase delay during the switching VLBI period is sufficiently accurate and, together with Doppler and range measurements, can be a useful means for precisely determining satellite orbits and precisely estimating the lunar gravity field.

The Exploration of Lunar Gravity by VLBI Observations of SELENE (Kaguya)

“…There were many opportunities to utilize the same beam differential VLBI method during this period and we have confirmed that the cycle ambiguity for the differential phase delay in the MFV method can be solved using the same beam differential VLBI method. An estimated differential phase delay for Okina and Ouna at 2212 MHz for the baseline between Ishigaki and Iriki stations is shown in Figure 6 as an example 18) . The error in the differential phase delay is smaller than 2 ps in a 30 s integration interval.…”