The Very Long Baseline Interferometry (VLBI) is an astronomical technique that combines radio signals from radio telescopes around the world for positioning and high-resolution imaging of deep space celestial objects and distant black holes.

Under the help of ZHANG Hongyu from the Computer Network and Information Center of the Chinese Academy of Sciences, and YANG Yuecheng from Yunnan Observatories, from May until early September 2019, the Radio Astronomy and VLBI research group have completed installation of the optical cable equipment and upgraded network equipment, and then tested the network. On September 17, 2019, LI Zhixuan and CHEN Wen from the group operated the 40-meter radio telescope to participate in broadband network transmission and real-time correlation observations of the European VLBI network, also called eVLBI observation.

This observation not only successfully participated in the previous test observations, but also participated in the follow-up scientific observations, and transmitted a large amount of long-baseline data to Chinese and foreign astronomers.

Compared with the traditional VLBI observation method which are disk recording and correlation processing after several weeks, the eVLBI observation reduces a lot of time for astronomers to wait for data correlation, which is extremely beneficial to the structural observation of various temporary sources with an outbreak duration of several days. It can promote the development of time domain astronomy.

In this eVLBI observation, the Kunming station transmitted the data to the correlation center in the Netherlands with a stable rate of about 1 gigabit per second via Beijing network center of CAS.

In addition to undertaking the VLBI and data transmission work of the China Lunar Exploration Project, the 40-meter telescope is also an important station of various international VLBI organizations, and often participates in various international VLBI joint observations. The success of this eVLBI observation greatly improved the ability of the Kunming 40-meter telescope to perform real-time observations, built the foundation for a higher-speed real-time observation of 2-6 Gbps (2-6 gigabits per second).

In the future, the Radio Astronomy and VLBI research Group will continue to upgrade the network hardware, to achieve super high-speed network real-time observation as soon as possible. 

The cross-correlation fringes of each channel obtained in real time are shown in the attached drawings. In the picture below, Ef stands for the 100m radio telescope in Effelsberg, Germany, and Km stands for Kunming. The spikes are correlation fringes and represent the synchronization of the time and frequency of the signals received by the two telescopes. The abscissa represents the relative time delay and the ordinate represents the correlation index. (IMAGE By CHEN Wen)

It shows the amplitude (bottom) and phase (top) of the fringes over time(IMAGE BY CHEN Wen)

Contact:

CHEN Wen, Yunnan Observatories, CAS