## 1 Introduction  
The Qinghai-Tibet Plateau (QTP), an inland plateau in Asia, is the largest plateau in China and the highest altitude in the world, known as the roof of the world. The dynamic and thermal effects of the QTP topography have an important impact on the weather and climate, atmospheric circulation, and water cycle worldwide. The generation, development, and eastward movement of mesoscale systems in the QTP may cause catastrophic weather, such as heavy rainfall in plateau and downstream areas [1]. Therefore, it is necessary to strengthen QTP atmospheric detection and obtain more abundant meteorological information, such as atmospheric temperature, pressure, and humidity. The remote sensingdetection of water vapour and liquid water content in the atmosphere has important applications in the fields of weather forecasting, artificial weather, and flight safety. Microwave remote sensing not only has the advantages of visible light and infrared remote sensing, but also has the unique advantages of all-weather and all-day conditions. For example, it can penetrate cloud cover, and dense fog and rainfall. Therefore, microwaves can be used to detect atmospheric conditions in the atmosphere and clouds with high detection sensitivity. Microwave radiometers (MWRs) adopt microwave remote sensing technology and are sensitive to the detection of atmospheric parameters such as temperature and humidity [2; 3]. This has practical significance for weather forecasting and artificial precipitation services. According to the working platform, MWR can be divided into two types, namely, space-based and ground-based systems. Based on satellite remote sensing technology in high-altitude orbits, the detected data have high spatial resolution and wide coverage, especially in land and marine areas where people are scarce [4; 5]. However, satellite detection is limited by the earth's geometry. It has high resolution at high altitudes, while the resolution at low altitudes is relatively poor [6; 7]. In particular, the shielding and strong absorption of clouds, as well as the opacity of the atmosphere to millimeter-wave-band electromagnetic waves, reduce the atmospheric detection accuracy at the bottom of the satellite troposphere. However, due to the limitation of the Earth's geometry, satellite remote sensing has high resolution at high altitudes, while the resolution at low altitudes is relatively poor. In particular, atmospheric detection at the bottom of the satellite troposphere is reduced due to the occlusion and strong absorption of clouds and the opacity of the atmosphere to the millimeter-wave-band electromagnetic wave [8]. In contrast, ground-based MWR is a supplement to satellite detection. The ground-based MWR can not only detect the temperature profile and water vapour density profile of the atmosphere in real time, but also retrieve the atmospheric integral water vapour content (_PWV_) and liquid water content (_LWC_) [2; 9; 10]. It can also conduct high-precision correction through the radio wave refraction error, and further investigate the spatial-temporal change rate and horizontal heterogeneity of the atmospheric refractive index. Compared with other traditional ground-based meteorological observation methods, such as sounding balloons and radars, MWR can achieve uninterrupted high temporal resolution and high detection accuracy of the atmosphere with low operation cost and no electromagnetic pollution [11; 12]. Therefore, ground-based MWR has been extensively used in the field of radiosonde observation. In 1988, [PERSON] [13] studied and discussed the accuracy of measuring liquid water by MWR and confirmed its feasibility, which opened up a new way for measuring the continuous distribution of vapour and liquid water in the atmosphere. [PERSON] [14] obtained the seasonal variation characteristics of total atmospheric water vapour and cloud liquid water through long-term experiments and tested the relationship between total atmospheric precipitable water vapour, cloud liquid water, and precipitation. [PERSON] et al.