Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua spacecraft have been successfully operating for nearly two decades and providing complementary observations of the Earth’s land, ocean, and atmosphere. Although the two MODIS instruments view the entire Earth’s surface once every 2–3 days, simultaneous views between them are limited due to their varying orbits. Therefore, the intercomparison between these two instruments has been previously performed using a transfer instrument [such as Advanced Very-high-resolution Radiometer (AVHRR)] or using lunar measurements normalized using a common model, such as the USGS Robotic Lunar Observatory (ROLO). In recent years RadCalNet, a Committee on Earth Observation Satellites (CEOS) initiative, has provided SI-traceable Top-of-Atmosphere (TOA) reflectances from a coordinated network of instrumented land-based sites. RadCalNet facilitates a unique mechanism to perform cross-calibration of instruments by minimizing the uncertainties associated with overpass time differences. In this letter, the near-simultaneous TOA reflectance measurements from the Railroad Valley (RRV), US (RVUS) are used as a transfer to compare the on-orbit observations for the Terra and Aqua MODIS reflective solar bands (RSBs). Near-nadir overpasses from January 2013 to January 2019 are processed and matched up with near-simultaneous RadCalNet measurements. Results show that the visible (VIS)/near-infrared response (NIR) bands agree to within 2%, and the short-wave infrared (SWIR) bands agree to within 5%. Also discussed in this letter are the future efforts that will be undertaken to expand this comparison to include other instruments, other sites, and both nadir- and off-nadir views after compensation for bidirectional reflectance distribution function (BRDF) effects.

中文翻译：

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使用 RadCalNet 对 Terra 和 Aqua MODIS 进行交叉校准

Terra 和 Aqua 航天器上的中分辨率成像光谱仪 (MODIS) 仪器已成功运行近二十年，并提供对地球陆地、海洋和大气的补充观测。尽管这两个 MODIS 仪器每 2-3 天观察整个地球表面一次，但由于轨道不同，它们之间的同时观察受到限制。因此，这两种仪器之间的比对以前是使用传输仪器[例如高级超高分辨率辐射计 (AVHRR)] 或使用使用通用模型归一化的月球测量值进行的，例如 USGS 机器人月球天文台 (ROLO) . 近年来，地球观测卫星委员会 (CEOS) 倡议 RadCalNet，已经提供了来自仪器化陆基站点的协调网络的 SI 可追踪的大气层 (TOA) 反射率。RadCalNet 通过最大限度地减少与立交桥时间差异相关的不确定性，促进了一种独特的机制来执行仪器的交叉校准。在这封信中，来自美国铁路谷 (RRV) (RVUS) 的几乎同时的 TOA 反射率测量值被用作比较 Terra 和 Aqua MODIS 反射太阳波段 (RSB) 在轨观测值的传输。从 2013 年 1 月到 2019 年 1 月的接近最低点的立交桥被处理并与几乎同时的 RadCalNet 测量相匹配。结果表明，可见（VIS）/近红外（NIR）波段一致在2%以内，短波红外（SWIR）波段一致在5%以内。