Improving simulations of Zeeman absorption spectrum for hyperspectral microwave sounding applications

Abstract. Accurate simulation of microwave oxygen absorption is critical for upper atmospheric remote sensing, yet traditional models suffer from biases due to simplified Zeeman splitting calculations. Two key advancements were presented to address this challenge. First, the 2024 RS-LBL model is updated with the Zeeman coefficients of Larsson et al. (2019), which capture higher-order rotational and anisotropic spin effects, thereby eliminating the 1 K bias in 7⁺ line simulations caused by the Hund’s case (b) approximation. Second, a full vector radiative transfer equation with a complex propagation matrix is implemented to rigorously model polarization under Zeeman splitting, integrated with hybrid Lorentz-Gaussian broadening. Systematic sensitivity experiments quantify the impacts of magnetic field intensity, propagation angle, and frequency shift on polarized brightness temperatures. Leveraging these insights, the Hyperspectral Microwave Atmospheric Sounder (HMAS) is designed: a 60–63 GHz linearly polarized instrument comprising 150 channels, optimized to 39 composite channels for noise reduction. Performance benchmarks against SSMIS UAS channels confirm that HMAS delivers unprecedented vertical resolution with reduced noise, establishing it as an optimal payload concept for next-generation space exploration missions targeting the near space atmosphere.