Accuracy assessment of the two WVRs, Astrid and Konrad, at the Onsala Space Observatory

Two Water Vapour Radiometers (WVRs), Astrid and Konrad, have been operating at the Onsala Space Observatory during the time period 2013–2016. There are several data gaps due to different types of instrument failures and therefore we also use estimates of the equivalent zenith wet delay (ZWD) from the two GNSS reference stations: ONSA and ONS1. They provide an almost continuous time series during the four years. ZWD root-mean-square differences are 0.38 cm between ONSA and ONS1, 0.92 cm between ONS1 and Astrid, and 0.75 cm between ONS1 and Konrad. For the horizontal linear gradients we see correlation coefficients of the order of 0.9 between ONSA and ONS1 and 0.5 between ONS1 and Konrad.