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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.

天基遥感被广泛用于测量地球大气。这些测量大多是基于对大气分子和原子自然产生的光发射的检测。要正确解释这些测量，了解这些粒子中的光发射是如何发生的是至关重要的。一个称为发射截面的量是描述发射过程的一个关键参数。虽然这个参数有时可以从观察中推断出来，但在受控环境中的实验室测量对于为这种参数提供一个确定的估计是必不可少的。该项目的目标是确定NASA航天器遥感观测地球日光所需的紫外线发射截面。在白天，来自卫星紫外线观测的O/N 2柱密度比的一个独特特征来自OI(135.6 nm)和N 2 Lyman-Birge-Hopfield(12 5-2 5 0 nm)波段系统的强度比，两者都是光学禁止发射。O/N 2柱密度比是了解全球范围内电离层和热层组成在所有地磁条件下从地球轨道卫星，例如GOLD(全球范围的肢体和盘观测)发生变化的关键。该团队在上一个资助期的研究表明，在过去50年里，实验室光谱学一直未能测量级联诱导的紫外线光谱，并未能确定LBH振动强度或级联发射截面，它占地球上最强的FUV发射总发射截面的约30%。这一失败在文献中引发了一场持续了十多年的争论，这是由于地面气辉观测和正演模型计算之间的二分法。该项目团队在实验室中测量了30-200 eV电子激发的氮气LBH能带系统的FUV级联感应谱。级联跃迁从两个过程开始：涉及两个态(a和w)的辐射和碰撞诱导电子跃迁(CIET)，随后是级联诱导跃迁aX。在这个项目中，该团队将研究从10-30 eV的阈值发射截面。这个项目的独特之处在于，使用一种特殊的仪器，更准确地测量了原子O和分子N 2的绝对发射截面QEM(总发射截面)和级联诱导截面QCasc(级联诱导截面)，该设备的碰撞腔比以前的实验室测量大了10倍，以便在相同的实验条件下正确地解释级联贡献。LASP的实验室光谱学迈出了不朽的一步，首次测量了N 2的光学禁止级联诱导UV光谱。然而，要完成从第一腔(0.75米半径)开始的LBH和其他重要的光学禁止跃迁的研究，还需要做很多工作。第二个腔体的半径为2米(是第一个腔体的两倍多)，这为原子和分子物理学开辟了一个全新的领域。过去50年，实验室研究单次散射电子碰撞诱导荧光光谱的寿命范围为1-100 ns(主要允许紫外光电子跃迁)。利用科罗拉多大学的两个大型真空室，可以研究寿命到10ms的更高禁带跃迁，以捕捉100ms的全部光发射和部分光发射，并能够建模到1000ms。这一涉及光学禁忌跃迁的新物理领域允许研究以前从未在单次散射条件下测量到的光谱，例如来自LBH的光谱、CO的卡梅隆带和N_2的Vegard-Kaplan带系统。这项提议的个人资料在测量地球和行星大气感兴趣的原子和分子的绝对QEM和QCasc方面有着广泛的50年跟踪记录。实验和模拟的多方面方法保证了一个关键的热层参数(O/n2)，以了解地球热层并将范围扩展到其他行星大气。该项目团队的数据为当前和未来的卫星任务(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))的高分辨率研究提供了基准参考。该奖项反映了NSF的法定任务，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。