Development of a fast radiative transfer model for ground-based microwave radiometers (ARMS-gb v1.0): validation and comparison to RTTOV-gb

Abstract. This study proposes a fast radiative transfer model, the Advanced Radiative Transfer Modeling System – ground-based (ARMS-gb), designed to simulate brightness temperatures observed by ground-based microwave radiometers. ARMS-gb employs a clear-sky radiative transfer solver to account for atmospheric thermal emissions, while gaseous absorption is estimated using a statistical regression scheme. To enhance simulation accuracy, particularly in moist environments, seven humid profiles from the University of Maryland, Baltimore County 48-profile dataset are added to the European Centre for Medium-Range Weather Forecasts 83-profile dataset to train the gaseous absorption scheme. Additionally, an advanced water vapor vertical interpolation method is incorporated, offering improved accuracy compared to the interpolation method used in Radiative Transfer for TOVS (RTTOV)-gb. The standard deviation is reduced by 0.15 K in channels with strong water vapor absorption. The Jacobians calculated by these two interpolation modes are also different. To further validate ARMS-gb's performance, simulations using both ARMS-gb and RTTOV-gb are compared against real observations from two ground-based microwave radiometers. The observation minus background analyses demonstrates that ARMS-gb aligns well with RTTOV-gb and achieves smaller standard deviations under high-humidity conditions. Furthermore, the capability of ARMS-gb to monitor the observational quality of ground-based microwave radiometers is demonstrated.