The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Aqua and Terra satellites have been operated for nearly two decades, producing high-quality earth observation data sets suitable for a broad range of scientific studies regarding the earth’s land, ocean, and atmospheric processes. The high radiometric accuracy of MODIS reflective solar band (RSB) calibration has also served as benchmark measurements for on-orbit cross-calibration studies. As the two MODIS instruments have operated well beyond their design lifespan of six years, the measurements from the onboard calibrators alone become inadequate to characterize the sensor’s response at all scan angles, as evinced by long-term drifts observed at certain scan positions of the Aqua-MODIS 0.64- and 0.86- $\mu \text{m}$ bands in Collection 6 (C6) data set. The latest MODIS Level 1B C6.1 data set incorporates earth-view response trending from invariant desert sites as supplemental inputs to characterize the scan-angle calibration dependencies for all RSB. This article presents a deep convective cloud (DCC)-based calibration approach for an independent evaluation of the MODIS RSB response versus scan-angle (RVS) performance in C6.1. The long-term calibration stability and RVS differences in C6.1 have been significantly improved for Aqua-MODIS RSB. The observed RVS differences of more than 2% in Aqua-MODIS C6 bands 1 and 2 have been reduced to within 1% in C6.1. Some RSBs of Terra-MODIS have suffered temporal drifts up to ~2% and calibration shifts up to 3%, particularly around 2016 when the Terra satellite entered into safe mode. The DCC approach has been found very effective in tracking the on-orbit RVS changes over time.

中文翻译：

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收集 6.1 校准中 MODIS 反射太阳波段的响应与扫描角度评估

Aqua 和 Terra 卫星上的中分辨率成像光谱仪 (MODIS) 仪器已经运行了近二十年，产生了高质量的地球观测数据集，适用于有关地球陆地、海洋和大气过程的广泛科学研究。MODIS 反射太阳波段 (RSB) 校准的高辐射精度也已作为在轨交叉校准研究的基准测量。由于两台 MODIS 仪器的运行已远远超出其 6 年的设计寿命，因此单凭机载校准器的测量结果不足以表征传感器在所有扫描角度的响应，在 Aqua 的某些扫描位置观察到的长期漂移证明了这一点。 -MODIS 0.64- 和 0.86- $\mu \text{m}$ 集合 6 (C6) 数据集中的波段。最新的 MODIS Level 1B C6.1 数据集结合了来自不变沙漠站点的地球视图响应趋势作为补充输入，以表征所有 RSB 的扫描角度校准相关性。本文介绍了一种基于深对流云 (DCC) 的校准方法，用于独立评估 C6.1 中 MODIS RSB 响应与扫描角 (RVS) 的性能。Aqua-MODIS RSB 在 C6.1 中的长期校准稳定性和 RVS 差异已得到显着改善。在 Aqua-MODIS C6 波段 1 和 2 中观察到的超过 2% 的 RVS 差异在 C6.1 中已减少到 1% 以内。Terra-MODIS 的一些 RSB 遭受了高达约 2% 的时间漂移​​和高达 3% 的校准偏移，特别是在 2016 年左右，当 Terra 卫星进入安全模式时。