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

合作研究：通过粒子撞击实验室测量氧气 (O) 和氮气 (N2) 紫外线 (UV) 截面，以遥感热层 O/N2 变化

基本信息

批准号：
2031349
负责人：
Joseph Ajello
金额：
$ 69.8万
依托单位：
University of Colorado at Boulder
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-09-15 至 2024-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2031349&HistoricalAwards=false
关键词：
Collaborative Research Laboratory Measurements Oxygen

项目摘要

Space-based remote sensing is widely used to measure the Earth’s atmosphere. Most of these measurements are based on detection of naturally occurring light emissions from the atmospheric molecules and atoms. To interpret these measurements correctly, understanding how the light emission occurs in these particles is of fundamental importance. A quantity called emission cross section is a key parameter that describes the emission process. While this parameter can sometimes be inferred from observation, laboratory measurement in a controlled environment is essential to provide a definitive estimate for such parameter. The goal of this project is to determine the UV emission cross sections needed for remote sensing observations of the Earth’s dayglow by NASA spacecraft. In the dayglow, a unique signature of the O/N2 column density ratio, derived from satellite-based UV observations, comes from the intensity ratio of the OI (135.6 nm) and N2 Lyman-Birge-Hopfield (LBH) band system (125-250 nm), both optically forbidden emissions. The O/N2 column density ratio is key to understanding ionosphere and thermosphere composition changes on a global scale under all geomagnetic conditions from Earth-orbiting satellites, e.g. GOLD (Global-scale Observation of the Limb and Disk). The team’s research in the last funding period shows laboratory spectroscopy for the past 50-years has failed to measure the cascade-induced UV spectrum and determine LBH vibrational intensities or cascade emission cross sections, which accounts for ~30% of the total emission cross section, of the Earth’s strongest FUV emission. This failure has precipitated a controversy in the literature that has persisted for over a decade due to the dichotomy between terrestrial airglow observations and forward model calculations. The project team have measured in the laboratory the FUV cascade-induced spectrum of the LBH band system of N2 excited by 30–200 eV electrons. The cascading transition begins with two processes: radiative and collision-induced electronic transitions (CIETs) involving two states (a and w), which are followed by a cascade induced transition a X. In this project, the team will investigate the threshold emission cross sections from 10-30 eV. The uniqueness of this project 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 a special apparatus designed with a ten times bigger collision chamber than previous laboratory measurements to properly account for the cascade contributions under the same experimental conditions.Laboratory spectroscopy at LASP has made a monumental step by measuring the optically-forbidden cascade-induced UV spectrum of N2 for the first time. However, much work needs to be done to complete the study of LBH and other important optically forbidden transitions that began in the first chamber (0.75 m radius). The second chamber with a radius of 2 m (more than double that of the first chamber) allows a whole new realm of atomic and molecular physics. The lifetime ranges available for laboratory studies of single scattering electron impact induced fluorescence spectra were 1-100ns (mainly allowed UV electronic transitions) for the past 50 years prior. With two large vacuum chambers at the University of Colorado even more highly forbidden transitions with lifetimes to 10ms can be studied to capture the full light emission and partial light emission to 100ms with an ability to model to 1000ms. This new field of physics involving optically forbidden transitions allows the study of spectra never before measured in single-scattering conditions such as that from LBH, the Cameron Bands of CO and Vegard-Kaplan band system of N2. The PIs of this proposal have an extensive 50 year track record of measuring the absolute Qem and Qcasc for atoms and molecules of interest to Earth and planetary atmospheres. The multi-facet approaches of both experiment and modeling promise a critical thermosphere parameter (O/N2) for an understanding of the Earth’s thermosphere and extending in scope to other planetary atmospheres. The project team’s data provides a bench-mark reference for high resolution studies by current and future satellite missions (e.g., Atmosphere-Space Interactions Monitor (ASIM) carrying a suite of instruments on the International Space Station).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.

天基遥感广泛用于测量地球大气层，大多数测量都是基于对大气分子和原子自然发生的光发射的检测，为了正确解释这些测量结果，需要了解这些粒子中的光发射是如何发生的。称为发射截面的量是描述发射过程的关键参数，虽然有时可以通过观察推断出该参数，但在受控环境中进行实验室测量对于提供此类参数的明确估计至关重要。该项目旨在确定远程所需的紫外线发射截面NASA 航天器对地球日光的传感观测在日光中，O/N2 柱密度比的独特特征源自卫星紫外线观测，来自 OI (135.6 nm) 和 N2 Lyman- 的强度比。 Birge-Hopfield (LBH) 波段系统 (125-250 nm)，均为光学禁发射 O/N2 柱密度比是了解全球电离层和热气层组成变化的关键。该团队在上一个资助期间的研究表明，过去 50 年的实验室光谱学未能测量级联引起的现象。紫外光谱并确定 LBH 振动强度或级联发射截面，约占地球上最强 FUV 总发射截面的 30%由于地面气辉观测和前向模型计算之间的二分法，这一失败在文献中引发了一场持续了十多年的争论。 N2 由 30-200 eV 电子激发的级联跃迁涉及两个过程：辐射和碰撞引起的电子跃迁 (CIET) 两种状态（a 和）。 w)，随后是级联诱导跃迁 a X。在该项目中，该团队将研究 10-30 eV 的阈值发射截面。该项目的独特之处在于原子 O 和分子 N2 绝对值的测量。使用比以前的实验室测量大十倍的碰撞室设计的特殊设备，可以更准确地计算 Qem（总发射截面）和 Qcasc（级联诱导截面），以正确解释相同实验条件下的级联贡献。实验室LASP 的光谱学首次测量了 N2 的光禁级联诱导紫外光谱，迈出了里程碑式的一步。然而，要完成 LBH 和其他重要的光禁跃跃迁的研究还需要做很多工作。第一个室（半径为 0.75 m）。第二个室的半径为 2 m（是第一个室的两倍以上），为原子和分子物理的实验室研究提供了一个全新的领域。过去 50 年来，散射电子碰撞诱导荧光光谱为 1-100 纳秒（主要允许紫外电子跃迁），科罗拉多大学的两个大型真空室甚至可以研究寿命为 10 毫秒的高度禁戒跃迁，以捕获完整的光谱。光发射和部分光发射可达 100ms，能够模拟 1000ms 这个涉及光学禁戒跃迁的新物理领域允许研究以前在单散射条件下测量的光谱。例如 LBH、CO 的卡梅伦能带和 N2 的 Vegard-Kaplan 能带系统。该提案的 PI 拥有 50 年测量地球和行星大气感兴趣的原子和分子的绝对 Qem 和 Qcasc 的广泛记录。实验和建模的多方面方法为了解地球热层并将其范围扩展到其他行星大气层提供了关键的热层参数（O/N2）。为当前和未来卫星任务的高分辨率研究提供基准参考（例如，在国际空间站上携带一套仪器的大气-空间相互作用监测器（ASIM））。该奖项反映了 NSF 的法定使命，并被认为值得支持通过使用基金会的智力优点和更广泛的影响审查标准进行评估。