Single-band VLBI Absolute Astrometry

Abstract The ionospheric path delay impacts single-band, very long baseline interferometry (VLBI) group delays, which limits their applicability for absolute astrometry. I consider two important cases: when observations are made simultaneously in bands, but delays only one band available a subset of observations; and one-band design. developed optimal procedures data analysis both cases using Global Navigation Satellite System (GNSS) ionosphere maps, provided stochastic model that describes errors, evaluated impact on source position estimates. demonstrate the is accurate at level 15%. found GNSS maps as introduces serious biases estimates declination procedure almost eliminates them. serendipitously have multiplicative errors to be scaled by 0.85 order mitigate bias. A similar scale factor was comparison vertical total electron content from satellite altimetry against maps. favor interpretation this scaling manifestation inadequacy thin-shell ionosphere. showed we able extent no noticeable systematic emerge assess adequately contribution ionosphere-driven random positions. This makes single-band astrometry viable option can used determination.