Features and advantages of very long baseline interferometry
1. The VLBI delay and delay rate are pure geometric observations, which do not contain information about the earth's gravitational field, so the acquisition of the observations is not affected by the earth's gravitational field.
2. VLBI is a relative measurement. Only using VLBI technology can only determine the relative position between the two antennas, that is, the baseline vector b.
3. In order to determine the geocentric coordinates of the VLBI station, VLBI and Satellite Laser Ranging (SLR) observations are usually carried out simultaneously on one station, that is, juxtaposed observations, and the geocentric coordinates measured by SLR technology As a reference, further calculate the geocentric coordinates of other VLBI stations.
4. Because there is a direct relationship between the right ascension α of the radio source and the change of the earth's rotation, it cannot be independently solved from the delay and delay rate observations. Therefore, the VLBI technology cannot independently determine the origin of right ascension of the radio reference system, it must be determined by other techniques.
5. The influence of the baseline component Z is not included in the delay rate observation. Therefore, the baseline component Z cannot be calculated by delay rate observation alone. In addition, adding the delay rate data to the delay data does not reduce the number of radio sources to be observed to obtain all unknown parameters. The delay rate is only used as an auxiliary observation to participate in data processing and parameter calculation, and the decisive role is the delay observation.