Development of A Fast Radiative Transfer Model for Ground-based Microwave Radiometers (ARMS-gb v1.0): Validation and Comparison to RTTOV-gb

Abstract. A fast radiative transfer model (RTM), ARMS-gb, capable of simulating brightness temperatures observed by ground-based microwave radiometers (GMRs) is proposed in this study. Several improvements are introduced in the Optical Depth in Pressure Space scheme to achieve higher accuracy. 101-level ECMWF 83 profiles are utilized as its primary training dataset. Seven additional profiles from UMBC 48 are augmented with this dataset to improve simulation accuracy in moist environments. When compared to MonoRTM, ARMS-gb shows high accuracy with root mean square error less than 0.12 K for all observed channels of MP3000A and HATPRO. An advanced water vapor vertical interpolation mode is also incorporated, which generally proves more accurate than that used in RTTOV-gb. Bias drops can reach up to 0.19 K for mean biases (AVG) and 0.15 K for standard deviation (STD) in channels with strong water vapor absorption. Jacobian calculated by these two modes are also differ. To further validate the performance of ARMS-gb, it is applied in simulating real observations from GMRs, with the simulated results compared to those of RTTOV-gb. Long-term observations from two GMRs under different climate conditions are selected as true reference values. Results show that ARMS-gb align with RTTOV-gb well and can achieve smaller STD in water vapor absorption channels. Furthermore, the calibration time is more clearly identified in the observations minus background series of ARMS-gb compared to original observation series, demonstrating its ability to monitor observational quality.