CEDAR: A Robust Interferometer for Studies of Thermospheric Composition and Dynamics

研究人员将开发一种程序，利用地面对844.6纳米鲍恩荧光发射的观测，结合非相干散射雷达测量和数值模型，测量高层大气中的原子氧浓度。中性大气在几乎所有的热层过程中都起着重要的作用，在250-500公里范围内，氧是主要的中性物质。它在从热层动力学到热层-电离层相互作用，再到航天器运行的各种情况下都很重要。然而，在过去的二十年里，中性氧密度[O]的测定在很大程度上依赖于半经验大气模型，如质谱仪非相干散射(MSIS)理论，该理论得到了20年前卫星质谱仪数据的支持。虽然这种方法相当有用，但它们对统计平均值的依赖导致它们的预测存在很大的不确定性，特别是在磁暴等可变现象期间。这项研究将使用正向模型和地面非相干散射雷达和光学气辉测量来测量原子氧。光学测量将使用空间外差光谱仪(SHS)进行，这是一种新型的傅里叶变换光谱仪，无需扫描即可在广泛的波长范围内提供出色的干涉性能。SHS类似于传统的干涉仪(迈克尔逊、法布里-珀罗)，因为它比光栅光谱仪更紧凑，在给定的分辨率下有更高的拉伸度。然而，在没有扫描的情况下，它可以制造出比传统干涉仪更坚固的产品，在关键光学部件上具有宽松的平面度公差。此外，与迈克尔逊不同的是，SHS可以从一次观测调整到下一次观测，从而使其变换后的光谱中心始终落在科学线附近。因此，单个SHS可以在许多波长区域产生易于采样的条纹。而且，通过一些其他的微小调整，一个SHS可以比单一的法布里-珀罗系统更有效地观测到上述气辉排放。它也可以在成像模式下使用。同样的仪器还可以测量630、732和1129纳米附近的其他气辉排放，提供关于关键热层过程和全球风的更多信息。

The investigators will develop a procedure for measuring atomic oxygen concentrations in the upper atmosphere using ground-based observations of 844.6 nanometer Bowen fluorescence emissions, combined with incoherent scatter radar measurements and a numerical model. The neutral atmosphere plays a significant role in almost every thermospheric process, and oxygen is the dominant neutral species between 250 and 500 km. It is important in contexts ranging from thermospheric dynamics, to thermospheric-ionospheric interaction, to spacecraft operation. Yet, for the last two decades, determination of neutral oxygen density, [O], has relied heavily on semi-empirical atmospheric models like the Mass Spectrometer Incoherent Scatter (MSIS) theory, supported by 20-year-old satellite mass spectrometer data. While such methods are rather useful, their reliance on statistical averages leads to substantial uncertainties in their predictions, especially during variable phenomena such as magnetic storms. This study will measure atomic oxygen using a forward model and ground-based incoherent scatter radar and optical airglow measurements. The optical measurements will be made with a Spatial Heterodyne Spectrometer (SHS), which is a novel Fourier transform spectrometer that provides outstanding interferometric performance over a broad range of wavelengths without scanning. The SHS is like conventional interferometers (Michelson, Fabry- Perot), in that it is more compact with higher etendue at a given resolving power than grating spectrometers. However, being unscanned, it can be built far more robust than conventional interferometers, with relaxed flatness tolerances on critical optics. Moreover, unlike Michelsons, the SHS can be adjusted from one observation to the next so that the center of its transformed spectrum always falls near the science lines. A single SHS may thus produce easy-to-sample fringes in many wavelength regions. And, with a few other minor adjustments, one SHS can observe the airglow emissions mentioned above far more efficiently than a single Fabry-Perot system. It can also be used in an imaging mode. The same instrument can also measure other airglow emissions near 630, 732, and 1129 nanometer, providing even more information about crucial thermospheric processes and global winds.