The accuracy of geodetic Very Long Baseline Interferometry (VLBI) is affected by water vapour in the atmosphere in terms of variations in the signal propagation delay at the different stations. This “wet” delay may be estimated directly from the VLBI data, as well as from independent instruments, such as collocated microwave radiometers. Rather than having stand-alone microwave radiometers we have, through simulations, evaluated the possibility to use radiometric data from the VLBI receiver in the VGOS telescopes at the Onsala Space Observatory. The advantage is that the emission from water vapour, as sensed by the radiometer, originates from the same atmospheric volume that delays the VLBI signal from the extra-galactic object. We use simulations of the sky brightness temperature and the wet delay together with an assumption of a root-mean-square (rms) noise of the receiver of 1 K, and observations evenly spread between elevation angles of 10\(^\circ \)–90\(^\circ \). This results in an rms error of the estimated equivalent zenith wet delay of the order of 3 mm for a one frequency algorithm, used under cloud free conditions, and 4 mm for a two frequency algorithm, used during conditions with liquid water clouds. The results exclude rainy conditions when the method does not work. These errors are reduced by a factor of 3 if the receiver error is 0.1 K meaning that the receivers’ measurements of the sky brightness temperature is the main error source. We study the impact of ground-noise pickup by using a model of an existing wideband feed. Taking the algorithm uncertainty and the ground noise pickup into account we conclude that the method presented will be useful as an independent estimate of the wet delay to assess the quality of the wet delays and linear horizontal gradients estimated from the VLBI data themselves.

大地测量甚长基线干涉测量法 (VLBI) 的精度受大气中水汽的影响，这取决于不同站的信号传播延迟的变化。这种“湿”延迟可以直接根据 VLBI 数据以及独立仪器（例如并置的微波辐射计）进行估计。我们没有使用独立的微波辐射计，而是通过模拟评估了使用来自 Onsala 空间天文台 VGOS 望远镜中 VLBI 接收器的辐射测量数据的可能性。其优点是辐射计检测到的水蒸气发射来自相同的大气体积，它延迟了来自银河系外物体的 VLBI 信号。\(^\circ \) –90 \(^\circ \). 这导致估计等效天顶湿延迟的均方根误差对于在无云条件下使用的单频算法为 3 毫米，而对于双频算法（在有液态水云的条件下使用）为 4 毫米。当该方法不起作用时，结果不包括雨天条件。如果接收器误差为 0.1 K，则这些误差将减少 3 倍，这意味着接收器对天空亮温的测量是主要误差源。我们通过使用现有宽带馈电模型研究地面噪声拾取的影响。