The thermal infrared (TIR) emissivity and physical temperature of snow together determine the thermal radiation of snow. The modeling of snow and ice TIR emissivity is important for climate models and remote sensing. Previous snow and ice TIR emissivity models fail in predicting the sensitivity of emissivity to snow type and snow microstructure, which was measured in experiments. Empirical models were proposed to simulate such sensitivity but not in a unified theoretical framework. In this study, we propose a snow and ice TIR emissivity model based on photon tracking by assuming that the geometric optics approximation is still valid in TIR spectral region. It is proved that the proposed model can predict both the TIR emissivity’s sensitivity to grain size for small grain sizes and the TIR emissivity’s sensitivity to snow density. These features can fully explain the experiment observed features. Moreover, the proposed model simulates snow and ice TIR emissivity in a unified theoretical framework. We also explain that the observed emissivity’s sensitivity to snow type is actually caused by the sensitivity to snow density, not grain size. This proposed model can be further used in climate models and remote sensing.

中文翻译：

---

使用光子跟踪模拟雪和冰的热红外发射率


雪的热红外（TIR）发射率和物理温度共同决定了雪的热辐射。冰雪 TIR 发射率建模对于气候模型和遥感非常重要。以前的雪和冰 TIR 发射率模型无法预测发射率对雪类型和雪微观结构的敏感性，这是在实验中测量的。人们提出了经验模型来模拟这种敏感性，但没有在统一的理论框架中进行。在本研究中，我们假设几何光学近似在 TIR 光谱区域仍然有效，提出了一种基于光子跟踪的雪和冰 TIR 发射率模型。事实证明，该模型可以预测小晶粒尺寸下 TIR 发射率对晶粒尺寸的敏感性以及 TIR 发射率对雪密度的敏感性。这些特征可以充分解释实验观察到的特征。此外，所提出的模型在统一的理论框架中模拟了雪和冰的 TIR 发射率。我们还解释说，观测到的发射率对雪类型的敏感性实际上是由对雪密度的敏感性引起的，而不是颗粒尺寸。该模型可进一步用于气候模型和遥感。