An algorithm of wideband bandwidth synthesis for geodetic VLBI

Abstract

A practical algorithm for wideband bandwidth synthesis (WBWS) for geodetic VLBI (very long baseline interferometry) is presented in this paper. A conventional bandwidth synthesis technique was developed for geodetic VLBI in the 1970s in order to increase the resolution of the observed delay by synthesizing multiple receiving frequency windows. The synthesized bandwidth has been expanding over the years and is now about 1 GHz. Recently, a wideband VLBI system consisting of multiple wideband frequency windows with a width of 1 GHz each and a total bandwidth exceeding 10 GHz has been proposed by the International VLBI Service for Geodesy and Astrometry (IVS) in order to achieve millimeter precision of position measurements. WBWS is a technique used for data processing in a wideband VLBI system. In conventional bandwidth synthesis, phase calibration (PCAL) signals are artificially injected at a front end and used to synthesize the channels. However, an algorithm without the use of PCAL signals was developed for WBWS so that it can be applied to a system without PCAL equipment. The algorithm includes the estimation of the differential total electron content in the ionosphere working with data with signal-to-noise ratios as low as 10 per band. The algorithm was successfully applied to 24 h continuous wideband VLBI observations.