Collaborative Research: Laboratory Measurements of Oxygen (O) and Nitrogen (N2) Ultraviolet (UV) Cross Sections by Particle Impact for Remote Sensing of Thermosphere O/N2 Variation

地球上层大气中发生的各种化学反应会产生多种波长范围很广的辐射。这些在文献中被称为气辉，是高纬度地区壮观的极光的原因。卫星上的精密仪器和地面系统已被用来监测这些排放，以调查这些排放产生的区域。远紫外辐射（FUV）已被用于探测地球热层-电离层系统的遥感技术，特别是卫星。其中包括来自OI 135.6 nm和N2 Lyman-Birge-Hopfield （LBH）振动带的贡献。全球尺度翼盘观测（GOLD）任务在~ 132 ~ 160 nm的FUV波段进行光谱成像，提供了白天温度（TDisk）和O/N2组成的测量结果。为了利用卫星任务更准确地确定地球热层-电离层的组成和温度变化，必须准确地确定发射截面及其辐射寿命。该计划的主要目标是确定紫外线发射截面，以精确模拟地球日光的遥感观测。随着地球物理遥感技术的进步和远紫外（FUV: 125.0-250.0 nm）观测在空间天气方面的重要发现，具有成像能力的紫外光谱方法在实验室和地面观测中都扮演着越来越重要的角色。科罗拉多大学（CU）正在进行的GOLD任务使用OI （135.6 nm）和N2 Lyman-Birge-Hopfield （LBH）波段系统（125-250 nm）的日光紫外线观测，两者都是光学禁止发射。利用这些辐射导出了产生光电子的入射太阳通量（QEUV）的代理。在日光中，O/N2柱密度比的独特特征来自于基于卫星的UV观测，OI （135.6 nm）和N2 LBH波段系统（125-250 nm）之间的强度比都是光学禁止发射。O/N2柱密度比和热层温度测量是利用GOLD等地球轨道卫星了解所有地磁条件下全球尺度电离层和热层组成和动力变化的关键。未能准确测量发射截面导致了O/N2和QEUV反演的系统不确定度（O/N2报道为~ 30%）。这个提议的独特之处在于原子O和分子N2的绝对Qem（总发射截面）和Qcasc（级联诱导截面）的测量更精确，而设计的仪器用于解释级联的贡献（即，消除常见的错误，如壁碰撞）。这些测量将改进利用基于卫星的地面FUV测量对热层-电离层参数的推导。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A variety of chemical reactions occurring in the Earth’s upper atmosphere generate several emissions spanning a wide range of wavelengths. These are referred to as airglow in the literature and are responsible for the spectacular aurora at higher latitudes. Sophisticated instruments on-board satellites and ground-based systems have been used to monitor these emissions for investigating the regions where these emissions originate. Far ultraviolet emissions (FUV) have been used in remote sensing techniques for probing Earth’s thermosphere-ionosphere system, especially by satellites. These include contributions from OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) vibrational bands. Spectral imaging in the FUV bands ~ 132 – 160 nm by the Global-Scale Observations of the Limb and Disk (GOLD) mission provides daytime measurements of temperature (TDisk) and composition of O/N2. To enable a more accurate determination of composition and temperature changes of Earth’s thermosphere-ionosphere using satellite-based missions, an accurate determination of the emission cross-sections and their radiative lifetime are necessary. The primary goal for this program is to determine the UV emission cross sections needed to accurately model remote sensing observations of the Earth’s dayglow. As Geophysical remote sensing techniques have improved and observations of the far ultraviolet (FUV: 125.0–250.0 nm) have led to important discoveries in Space Weather, UV spectroscopy methods with imaging capability have assumed an increasingly important role in both the laboratory and Terrestrial observations. The ongoing GOLD mission built at the University of Colorado (CU) uses the dayglow UV observations of the OI (135.6 nm) and N2 Lyman-Birge-Hopfield (LBH) band system (125-250 nm), both optically forbidden emissions. The proxy for the incident solar flux (QEUV) producing photoelectrons is derived using these emissions. In the dayglow, a unique signature of the O/N2 column density ratio are derived from satellite-based UV observations of the intensity ratio between the OI (135.6 nm) and N2 LBH band system (125-250 nm) both optically forbidden emissions. The O/N2 column density ratio and thermosphere temperature measurements are keys to understanding ionosphere and thermosphere composition and dynamical changes on a global scale under all geomagnetic conditions using Earth-orbiting satellites like GOLD. The failure to accurately measure the emission cross section contributes to the systematic uncertainty for O/N2 and QEUV retrievals (~ 30% reported for O/N2). The uniqueness of this proposal is the measurement of both the atomic O and molecular N2 absolute Qem (total emission cross section) and Qcasc (cascade-induced cross section) more accurately with an apparatus designed to account for cascade contributions (i.e., to eliminate common errors like wall collisions). These measurements will improve derivation of thermosphere-ionospheric parameters using satellite based terrestrial FUV measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.