Simulating Radiometric Resolution of Microwave Humidity and Temperature Sounder Onboard the FY-3D Satellite

Microwave humidity and temperature sounder (MWHTS) is an important payload of FENGYUN-3D (FY-3D) satellite. MWHTS is designed as a total power radiometer because of its high radiometric resolution (NEDT) and simple configuration. NEDT is one of the most important indicators for MWHTS. However, the traditional NEDT analysis results have a large error compared with the measured results. To estimate the overall radiometer performance, this article presents a numerical system simulation model that can be used to estimate NEDT. The model considers two of three main components that degrade the NEDT: thermal noise and calibration error. The third component $1/f$ noise is calculated by analyzing the power spectrum of the actual output voltage. Based on digital signal processing, this article presents a method for accurate system modeling, including radiation source modeling, frontend modeling, and backend modeling. The simulation model is validated by comparing the dynamic range, linearity, and standard deviation in output signals of the simulation system and actual instrument. In this article, the model has been applied to NEDT estimate of 15 MWHTS channels operating from 89 to 183 GHz. The comparison of the estimate results between the simulation model and actual instrument shows they are in good agreement and the maximum error is no more than 18%.