Assessment of Radiative Transfer Models Based on Observed Brightness Temperature from Ground-Based Microwave Radiometer

Ground-based microwave radiometers (MWRs) have been widely used in recent years due to the fact that they provide atmospheric temperature and humidity profiles with high temporal resolutions. The quality of the multi-channel brightness temperature (TB) is the measure used to determine the quality of retrieved atmospheric profile products. In general, periodic absolute calibration using liquid nitrogen best maintains the quality of TB observations, but this operation is complex and difficult. As an auxiliary tool, radiative transfer model can be used to determine the TB quality of MWRs. Using observations from the Beijing radiosonde and two RPG MWRs located at the Beijing Observatory (GXT) in Beijing and the Xianghe site (XH) in Hebei, we evaluated three radiative transfer models—MonoRTM, ARTS, and MWRT—by comparing their simulations with those of the corresponding TBs observed at both sites. The results show that for most of the 14 MWR channels the simulations of the three models are highly consistent with the observed TBs (i.e., correlation coefficients up to 0.99), but for the temperature channels ch8 (51.26 GHz) and ch9 (52.28 GHz), there was a significant absolute deviation (approximately 4–5 K) between the simulated and observed TBs, and the correlation coefficient decreased significantly (<0.80), which indicates that the model simulation at these two channels must be improved. Of the three models, MonoRTM showed obvious systematic deviation at temperature channels ch8, ch9, and ch10 (53.86 GHz), particularly at ch8, which had a bias of up to 5 K. The ARTS model generated the worst simulation at the water vapor channel ch1 (22.24 GHz). The MWRT simulations were relatively more stable and closer to the corresponding TB observations at 14 channels, with the least systematic deviation. In addition, the locations of the radiosonde measurements differed from that of the MWR site, which had a significant impact on the simulations for the MWR’s water vapor channels. Comparisons of the observed and simulation TBs at both sites indicates that the observation quality of the water vapor channels for the MWR at GXT must be improved.