We introduce the cross spectrum based FRB (Fast Radio Burst) search method for VLBI observation. This method optimizes the fringe fitting scheme in geodetic VLBI data post processing, which fully utilizes the cross spectrum fringe phase information and therefore maximizes the power of single pulse signals. Working with cross spectrum greatly reduces the effect of radio frequency interference (RFI) compared with using auto spectrum. Single pulse detection confidence increases by cross identifying detections from multiple baselines. By combining the power of multiple baselines, we may improve the detection sensitivity. Our method is similar to that of coherent beam forming, but without the computational expense to form a great number of beams to cover the whole field of view of our telescopes. The data processing pipeline designed for this method is easy to implement and parallelize, which can be deployed in various kinds of VLBI observations. In particular, we point out that VGOS observations are very suitable for FRB search.

The ESA’s Mars Express solar corona experiments were performed at two solar conjunctions in the years 2015 and 2017 by a number of radio telescopes in the European VLBI Network. This paper presents the methods to measure the frequency and phase fluctuations of the spacecraft radio signal, and the applications to study the characteristics of the plasma turbulence effects on the signal at a single station and at multiple stations via cross correlation. The power spectra of the frequency fluctuations observed between 4.9 and 76.3 R s have a power-law shape close to a Kolmogorov spectrum over the frequency interval ν lo < ν < ν up, where the nominal value of ν lo is set to 3 mHz and ν up is in the range of 0.03–0.15 Hz. The rms of the frequency fluctuations is presented as a function of the heliocentric distance. Furthermore, we analyze the variations of the electron column density fluctuations at solar offsets 4.9 R s and 9.9 R s and the cross-correlation products between the VLBI stations. The power density of the differential fluctuations between different stations decreases at ν < 0.01 Hz. Finally, the fast flow speeds of solar wind >700 km s−1 are derived from the cross correlation of frequency fluctuations at ν < 0.01 Hz. The fast flow speeds of solar wind correspond to the high heliolatitude of the coronal region that the radio rays passed. The VLBI observations and analysis methods can be used to study the electron column density fluctuations and the turbulence at multiple spatial points in the inner solar wind by providing multiple lines of sight between the Earth and the spacecraft.

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The Chinese very long baseline interferometry net (CVN) has applied the delta differential one-way ranging (delta-DOR) radiometric tracking technique to determine the orbit of a lunar and a deep-space spacecraft. In the past observations, CVN had sometimes encountered a difficult observation situation that the DOR signals were extremely weak or severely interfered. The CVN FX correlator, usually cannot process these extremely weak DOR signals. In order to enhance the weak signal processing capability of CVN, here we report an alternative method called 'local correlation'. By this method, the distinct DOR signals structure features of the narrow bandwidth sinusoidal tone and their coherent phase, are used to extract the exact frequency and phase of each tone. We have adopted the method on the weak signal case, then compared with the results obtained from CVN FX correlator. Analysis result shows the local correlation method can process DOR tone at lower signal-to-noise ratios such as 1 dBHz. The method also has advantages of high anti-interference, low computation cost and high efficiency. Furthermore, the delta-DOR delay obtained from local correlation can improve the orbit accuracy and reduce the arc length required by the orbit determination after the trajectory course maneuver.