The geostationary Himawari-8 satellite offers a unique opportunity to monitor sub-daily thermal dynamics over Asia and Oceania, and several operational land surface temperature (LST) retrieval algorithms have been developed for this purpose. However, studies have reported inconsistency between LST data obtained from geostationary and polar-orbiting platforms, particularly for daytime LST, which can arise from variations in viewing geometries and inherent differences in sensor types and LST algorithms. Despite this, previous research has primarily focused on analysing the directionality of LST without thoroughly exploring systematic differences between platforms. Hence, we presented a Solar Zenith Angle-based Calibration (SZAC) method to harmonise the daytime component of a split-window retrieved Himawari-8 LST (referred to here as the baseline) with the MODerate-resolution Imaging Spectroradiometer (MODIS) LST. SZAC describes the spatial heterogeneity and magnitude of diurnal LST discrepancies from different platforms, which is anticipated to complement typical directionality analyses. We evaluated the harmonised LST data, referred to as the Australian National University LST with SZAC (ANU), against MODIS LST and the Visible Infrared Imaging Radiometer Suite (VIIRS) LST, as well as in-situ LST from the OzFlux network. Two peer Himawari-8 LST products from Chiba University and the Copernicus Global Land Service were also collected for comparison. The median daytime bias of ANU LST against Terra-MODIS LST, Aqua-MODIS LST and VIIRS LST was 1.52 K, 0.98 K and −0.63 K, respectively, which demonstrated improved performance compared to baseline (5.37 K, 4.85 K and 3.02 K, respectively) and Chiba LST (3.71 K, 2.90 K and 1.07 K, respectively). All four Himawari-8 LST products showed comparable performance of unbiased root mean squared error (ubRMSE), ranging from 2.47 to 3.07 K, compared to LST from polar-orbiting platforms. In the evaluation against in-situ LST, the mean values of bias (ubRMSE) of baseline, Chiba, Copernicus and ANU LST during daytime were 4.23 K (3.74 K), 2.16 K (3.62 K), 1.73 K (3.31 K) and 1.41 K (3.24 K), respectively, based on 171,289 hourly samples from 20 OzFlux sites across Australia between 01/Jan/2016 and 31/Dec/2020. In summary, the SZAC method offers a promising approach to enhance the reliability of geostationary LST retrievals by incorporating the spatiotemporal characteristics observed by accurate polar-orbiting LST data. SZAC can also reduce LST angular effects due to its capability of quantifying spatial inhomogeneity of surface heat dynamics. Furthermore, it is possible to implement SZAC using LST data acquired by geostationary satellites in other regions, e.g., Europe, Africa and Americas. This could improve our understanding of the error characteristics of coincident imageries from geostationary and polar-orbiting platforms, allowing for targeted refinements and global harmonisations to further enhance applicability.

中文翻译：

---

基于太阳天顶角的 Himawari-8 陆地表面温度校准，用于校正昼夜反演误差特征


对地静止 Himawari-8 卫星提供了监测亚洲和大洋洲亚日热动态的独特机会，并且为此目的开发了几种可操作的地表温度 (LST) 反演算法。然而，研究报告称，从地球静止平台和极轨平台获得的 LST 数据之间存在不一致，特别是白天的 LST，这可能是由于观察几何形状的变化以及传感器类型和 LST 算法的固有差异造成的。尽管如此，之前的研究主要集中于分析 LST 的方向性，而没有彻底探索平台之间的系统差异。因此，我们提出了一种基于太阳天顶角的校准 (SZAC) 方法，用于协调分窗检索的 Himawari-8 LST（此处称为基线）的白天部分与中分辨率成像光谱辐射计 (MODIS) LST。 SZAC 描述了不同平台的日间 LST 差异的空间异质性和幅度，预计将补充典型的方向性分析。我们根据 MODIS LST 和可见红外成像辐射计套件 (VIIRS) LST 以及来自 OzFlux 网络的现场 LST 评估了统一的 LST 数据（称为澳大利亚国立大学 LST 与 SZAC (ANU)）。还收集了千叶大学和哥白尼全球陆地服务公司的两个同行 Himawari-8 LST 产品进行比较。 ANU LST 相对于 Terra-MODIS LST、Aqua-MODIS LST 和 VIIRS LST 的白天偏差中值分别为 1.52 K、0.98 K 和 −0.63 K，这表明与基线（5.37 K、4.85 K 和 3.02 K，分别）和千叶 LST（分别为 3.71 K、2.90 K 和 1.07 K）。 与极轨平台的 LST 相比，所有四种 Himawari-8 LST 产品均表现出可比的无偏均方根误差 (ubRMSE) 性能，范围为 2.47 至 3.07 K。在针对原位 LST 的评估中，白天的基线、Chiba、Copernicus 和 ANU LST 的偏差平均值 (ubRMSE) 分别为 4.23 K (3.74 K)、2.16 K (3.62 K)、1.73 K (3.31 K) 和分别为 1.41 K (3.24 K)，基于 2016 年 1 月 1 日至 2020 年 12 月 31 日期间澳大利亚 20 个 OzFlux 站点的 171,289 个每小时样本。总之，SZAC 方法通过结合精确的极轨道 LST 数据观测到的时空特征，提供了一种有前景的方法来提高对地静止 LST 反演的可靠性。 SZAC 还可以减少 LST 角度效应，因为它能够量化表面热动力学的空间不均匀性。此外，可以使用其他地区（例如欧洲、非洲和美洲）的对地静止卫星获取的 LST 数据来实施 SZAC。这可以提高我们对地球静止和极轨平台重合图像误差特征的理解，从而可以进行有针对性的改进和全球协调，以进一步增强适用性。