Abstract Top-of-atmosphere (TOA) albedo is a fundamental component of Earth's energy budget. To date, long-term global land TOA albedo products with spatial resolution higher than 20-km are not available. In this study, we propose a novel algorithm to retrieve TOA albedo from multispectral imager observations acquired by Advanced Very High Resolution Radiometer (AVHRR), which provides the longest continuous record of global satellite observations since 1981. Direct estimation models were established first to derive instantaneous TOA broadband albedo under various atmospheric and surface conditions, including cloudy-sky, clear-sky (snow-free) and snow-cover conditions. To perform long-term series analysis, the instantaneous TOA albedo were then converted to daily/monthly mean values based on the diurnal curves from multi-year Clouds and the Earth's Radiant Energy System (CERES) 3-hourly flux dataset. Calibration differences between sequential AVHRR sensors were further mitigated by invariant targets normalization. The retrieved TOA albedo at 0.05° × 0.05° was validated against two TOA albedo datasets, CM SAF (Climate Monitoring Satellite Application Facility) flux data and CERES flux data, at spatial resolutions of 0.05° × 0.05°, 20 km × 20 km and 1° × 1°. The instantaneous TOA albedo had an overall Root-Mean-Square-Error (RMSE) of 0.047 when compared with 20-km CERES fluxes, whereas the 1° by 1° monthly mean TOA albedo showed closer agreements with both CM SAF and CERES, with RMSE ranging from 0.029 to 0.040 and from 0.022 to 0.031, respectively. Moreover, our product was found to be highly consistent with both CERES and CM SAF at long-term trend detection. The extensive validation indicated the robustness of our algorithm and subsequently, comparable data quality with existing datasets. With global coverage and long time series (1981–2017), our product is expected to provide valuable information for climate change studies.

中文翻译：

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由 AVHRR 数据生成的陆地大气顶部反照率的长期记录

摘要 大气顶 (TOA) 反照率是地球能量收支的基本组成部分。迄今为止，空间分辨率高于 20 公里的长期全球陆地 TOA 反照率产品尚不可用。在这项研究中，我们提出了一种新算法，用于从高级甚高分辨率辐射计 (AVHRR) 获取的多光谱成像仪观测中检索 TOA 反照率，该算法提供了自 1981 年以来全球卫星观测的最长连续记录。首先建立直接​​估计模型以推导出瞬时TOA 宽带反照率在各种大气和地表条件下，包括多云天空、晴天（无雪）和积雪条件。为了进行长期序列分析，然后，根据多年云和地球辐射能系统 (CERES) 3 小时通量数据集的昼夜曲线，将瞬时 TOA 反照率转换为日/月平均值。不变目标归一化进一步减轻了连续 AVHRR 传感器之间的校准差异。检索到的 0.05° × 0.05° 的 TOA 反照率针对两个 TOA 反照率数据集、CM SAF（气候监测卫星应用设施）通量数据和 CERES 通量数据进行了验证，空间分辨率为 0.05° × 0.05°、20 km × 20 km 和1° × 1°。与 20 公里 CERES 通量相比，瞬时 TOA 反照率的总体均方根误差 (RMSE) 为 0.047，而 1° x 1° 的月平均 TOA 反照率与 CM SAF 和 CERES 显示出更接近的一致性，其中RMSE 范围从 0.029 到 0.040 和从 0.022 到 0.031，分别。此外，我们的产品在长期趋势检测中与 CERES 和 CM SAF 高度一致。广泛的验证表明我们算法的稳健性以及随后的数据质量与现有数据集的可比性。我们的产品覆盖全球，时间序列较长（1981-2017），有望为气候变化研究提供有价值的信息。