1. Acceleration term at ASL FRING as a tool to improve space VLBI sensitivity
L. Kogan (NRAO), S. Likhachev, I. Girin, & V. Ladigin (ASC)
Special features of Space VLBI
Correlated flux can be small because of partial resolution of the source at a large baseline Space RT- Ground RT.
FRING is applied directly to the target source.
Position of the Space RT may not be known as good as of Ground RTs
Acceleration phase term for Space VLBI
So, the visibility phase of the baseline SRT-GRT can not be described by only initial phase, delay, and fringe rate.
The fringes may not be detected with low solution interval because of big rms of the noise.
Having increased the solution interval rms will decrease, but the fringe amplitude may be decreased if the acceleration term is not taken into account.
THEREFORE
Adding the acceleration term can allow to increase the solution interval at FRING and as the result improve the sensitivity (lower the detectable signal).
Simulation
We simulated the vlbi observation adding the extra phase into one of the antenna (SRT) including acceleration term.
The Astro Space Center (Moscow, Russia) software (ASL for Windows) was used to search for the acceleration term.
The following slides demonstrate the improvement of the sensitivity using acceleration term.
R.Linfield, J. Ulvestad, “Science Loss vs Reconstructed Orbit Acceleration Error for VSOP and RADIOASTRON”
JPL interoffice memo May 1994
J. Ulvestad , “VSOP Coherence Measured at VLBA Correlator , Jan 1998
J. Ulvestad, “Comparison of Predicted and Reconstructed Orbit for VSOP”, May 1998