Jianfeng Cao

Observing APOD with the AuScope VLBI Array

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype—suitable for practical observation tests—combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission.

Monitoring CE’3 Rover Movement Using Same-Beam Interferometry with China’s Deep Space Network

China’s Deep Space Network (DSN) was deployed in 2013, a high-accuracy interferometric tracking observable was successfully used for orbit determination in the CE’3 project. This chapter presents the results of the rover’s status monitoring by earth-based same-beam interferometry (SBI) measurement. Phase delay with a biased offset is induced to identify the rover’s movement status, which could be up to three orders of magnitude better than conventional group delay. Based on the tracking data within China’s DSN, the status of the rover including going ahead, turning over, and changing signal can be successfully identified with a higher resolution. Combined with baseline length within China’s DSN, the movement of the rover in the order of centimeters can be identified, which testifies the effectiveness of this technique and algorithm.

Lunar Satellite Orbit Measurement Based on Visual/Radio Fusion

A set of new orbit Measurement method was proposed based on the integration of high-resolution lunar surface imaging and ground-based radio measurement. Through the method, the advantage of stable tracking by radio measurements and the advantage of short-range measurement by onboard camera are expect to be fully integrated. The basic idea of the method is as following. First, combined with orbit constraints of a lunar high resolution imaging satellite, relying on optical imaging information and available reference images on the lunar surface, and based on the visual related theory of multi-view geometry and photogrammetry, the accurate location information of the satellite platform in a moment was calculated. Then, the location information was fused reasonably with satellite speed, range and angle by ground radio measurements. Thereby, a more flexible lunar orbiter orbit determination method than the existing methods was established. Currently, based on real data of “Chang’E II” satellite, visual/radio fusion-based orbit determination model were studied. Transfer relationship of the position and attitude between the satellite and imaging points on lunar surface was derived. Typical aspects of information fusion-based orbit determination were analyzed. Preliminary experimental results verify the feasibility of the proposed method. After parameter calibration, the partial positioning accuracy of “Chang’E II” is better than 100 m, variance limits at 30 m.