| 1. |
- Han, SongTao, et al.
(author)
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Fringe fitting and group delay determination for geodetic VLBI observations of DOR tones
- 2019
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In: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 63:5, s. 1754-1767
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Journal article (peer-reviewed)abstract
- Extracting the group and phase delays of interferometric observations produced in the Very Long Baseline Interferometry (VLBI) measurement concept requires a special fringe fitting and delay search algorithm for the recorded bandwidth. While fringe fitting is in use routinely for several megahertz wide channels in geodetic and astrometric VLBI with quasar observations, fringe fitting for artificial tones of very small bandwidth of artificial signals for Differential One-way Ranging (DOR) requires a different way of handling. In a project called Observing the Chang’E-3 Lander with VLBI (OCEL), the DOR tones emitted by the Chang’E-3 lander were observed in a standard geodetic VLBI mode with 8 or 4 MHz wide channels to maintain compatibility with the corresponding quasar observations. For these observations, we modified the existing fringe fitting program of the Haystack Observatory Processing Software (HOPS), fourfit, to properly handle narrow band DOR tones. The main motivations are that through this modification, the data of quasars and artificial radio sources can be processed in the existing geodetic analysis pipeline, and that the algorithm can be used for similar projects as well. In this paper, we describe the algorithm and show that the new algorithm produces much more reliable group delay results than using the standard fourfitalgorithm. This is done by a simulation test and in particular by processing of real observations. It is shown that in many cases, systematic deviations of several nanoseconds, which are seen with the standard fourfit algorithm, can be avoided. The ultimate benefit of the new procedure is demonstrated by reducing the errors in delay triangle closures by at least a factor of 3, which, in the OCEL case, is from ∼300 to ∼100 ps.
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| 2. |
- Klopotek, Grzegorz, 1990, et al.
(author)
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Position determination of the Chang’e 3 lander with geodetic VLBI
- 2019
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In: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 71:1
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Journal article (other academic/artistic)abstract
- We present results from the analysis of observations of the Chang’e 3 lander using geodetic Very Long Baseline Interferometry. The applied processing strategy as well as the limiting factors to our approach is discussed. We highlight the current precision of such observations and the accuracy of the estimated lunar-based parameters, i.e., the lunar lander’s Moon-fixed coordinates. Our result for the position of the lander is 44.1219 3 ∘ N , -19.51159∘E and -2637.3 m, with horizontal position uncertainties on the lunar surface of 8.9 m and 4.5 m in latitude and longitude, respectively. This result is in good agreement with the position derived from images taken by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter. Finally, we discuss potential improvements to our approach, which could be used to apply the presented concept to high-precision lunar positioning and studies of the Moon.[Figure not available: see fulltext.].
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