The extreme ultraviolet (EUV) imager, EUVI-B, on board the International Space Station (ISS) under the International Space Station–ionosphere-mesosphere-atmosphere plasmasphere cameras (ISS-IMAP) mission was originally intended to observe EUV emissions at 83.4 nm scattered by \({\mathrm O}^+\) ions. During the mission, EUVI-B occasionally detected evident EUV signals in the umbra of the Earth. However, the source of the signals has not been verified. To evaluate the effect of the 83.4 nm EUV, we conduct a Monte Carlo simulation which considers multiple scattering of the 83.4 nm EUV by \({\mathrm O}^+\) ions. In addition, we modeled the contribution of the 91.1 nm emission, which is due to recombination of \({\mathrm O}^{+}\) ions and electrons, because the 91.1 nm EUV might affect the measurement from EUVI-B due to the wavelength range covered. The results suggest that the effect of the 83.4 nm EUV is likely to be negligible while the 91.1 nm EUV explains the observations from EUVI-B morphologically and quantitatively. We therefore conclude that the EUV signals observed by EUVI-B in the umbra of the Earth can largely be attributed to 91.1 nm emission due to recombination. This conclusion would facilitate the use of the EUVI-B data for reconstructing the \({\mathrm O}^+\) density.

国际空间站-电离层-中间层-大气等离子层相机 (ISS-IMAP) 任务下的国际空间站 (ISS) 上的极紫外 (EUV) 成像仪 EUVI-B 最初旨在观察 83.4 nm 的 EUV 发射被\({\mathrm O}^+\)离子分散。在任务期间，EUVI-B 偶尔会在地球本影中检测到明显的 EUV 信号。但是，信号的来源尚未得到证实。为了评估 83.4 nm EUV 的影响，我们进行了蒙特卡罗模拟，该模拟考虑了\({\mathrm O}^+\)离子对 83.4 nm EUV 的多次散射。此外，我们模拟了 91.1 nm 发射的贡献，这是由于\({\mathrm O}^{+}\)离子和电子，因为 91.1 nm EUV 可能会由于覆盖的波长范围而影响 EUVI-B 的测量。结果表明，83.4 nm EUV 的影响可能可以忽略不计，而 91.1 nm EUV 从形态和数量上解释了 EUVI-B 的观察结果。因此，我们得出结论，EUVI-B 在地球本影中观察到的 EUV 信号在很大程度上可以归因于由于复合而产生的 91.1 nm 发射。该结论将有助于使用 EUVI-B 数据重建\({\mathrm O}^+\)密度。