CVN harddisk system and software correlator in e-VLBI experiments

This paper presents some e-VLBI progress of CVN (Chinese VLBI Network). Presently CVN consists of two fixed stations located in Shanghai Sheshan and Urumqi Nan-shan, one mobile station in Yunnan Kunming, and one 2-station hardware correlator (Shanghai correlator) in Shanghai Astronomical Observatory (SHAO). In 2003, a PC-based VLBI data recording and playback unit named CVN harddisk system was developed at SHAO and several systems were installed in CVN. Several e-VLBI experiments have been performed with this system since 2003. Now the Shanghai correlator is able to process the data from harddisks or tapes. Based on the CVN harddisk system, a prototype software correlator was developed and used in the station fringe checkout, the fringe search of the satellite signal and data processing. The first domestic 3-station delay, delay rate closure test of the satellite VLBI observation and the first domestic satellite orbit determination test using VLBI were successfully accomplished based on the results of the software correlator. Besides, the software correlator acts as the fringe guider of the Shanghai correlator. To satisfy the requirements of the Chinese lunar exploration project, CVN will be upgraded to a realtime VLBI network, including 4 stations and two new realtime correlators (hardware and software). e-VLBI will be applied to the lunar satellite navigation, as well as other geodetic and astronomical observations in the future.