We examine 3 yr of phase-function observations of water-ice clouds taken during the Aphelion Cloud Belt season by the Mars Science Laboratory (MSL). We derive lower-bound single-scattering phase functions for Mars years (MYs) 34, 35, and 36, over a range of scattering angles from 45° to 155°, expanding on the MY 34 phase function previously derived from MSL observations using the same method. We also modify the procedure used for MY 34 to make use of cloud opacity values derived from other MSL observations, often taken in conjunction with the phase-function observations. From these, we see little variability, both interannually and diurnally in the phase function at Gale Crater. We use our derived phase functions to attempt to constrain a dominant ice-crystal geometry by fitting a two-term Henyey–Greenstein function. In comparing to HG functions of Martian dust and modeled water-ice crystals, we see agreement especially with droxtal water-ice crystals, dust at Gale crater, and irregular volcanic glasses. This could be indicative of crystals composed of some irregular shape.

中文翻译：

---

火星科学实验室三年 ACB 相函数观测：年际和日变化以及对冰晶习性的限制

我们检查了火星科学实验室 (MSL) 在远日云带季节期间对水冰云进行的 3 年相函数观测。我们推导了火星年 (MY) 34、35 和 36 的下限单散射相位函数，散射角范围为 45° 到 155°，扩展了先前从 MSL 观测中使用以下公式导出的 MY 34 相位函数：同样的方法。我们还修改了 MY 34 所使用的程序，以利用从其他 MSL 观测得出的云不透明度值，这些值通常与相位函数观测结合使用。从这些数据中，我们发现盖尔陨石坑的相位函数在年际和日间变化不大。我们使用导出的相函数尝试通过拟合两项 Henyey-Greenstein 函数来约束占主导地位的冰晶几何形状。在与火星尘埃和模拟水冰晶体的 HG 函数进行比较时，我们特别发现与 Droxtal 水冰晶体、盖尔陨石坑的尘埃和不规则火山玻璃的一致性。这可能表明晶体由某种不规则形状组成。