Microwave radiometer observations for VGOS data processing

Since mid 2023, the Onsala Space Observatory is operating a new modern microwave radiometer, Greta, which is a commercial product of type HATPRO-G5. It is co-located with the other microwave radiometer, Konrad, which has been developed and built at Onsala. Konrad has been in operation since 2000 and is usually operated in so-called sky-mapping mode. The data of complete sky-scanning sequence are then analyzed together, providing zenith wet delay and wet horizontal gradient results with a temporal resolution of 5 minutes. This type of data are available for this study from the beginning of 2023 to July 2024. In addition to operating in a similar sky-mapping mode, the new radiometer Greta has been operated synchronised with VGOS observations during several VGOS 24 h sessions from the year 2023 to 2024. This means that Greta was performing measurements of the local atmosphere in the same direction as the VGOS telescopes at Onsala, thus providing slant wet delay measurements for each individual VGOS observation. Together with the slant hydrostatic delays, calculated from ground pressure measurements, the possibility to avoid estimating the delays due to the neutral atmosphere exists and are evaluated. We present an update of using these slant delays as external a priori information in the VGOS data analysis.