Multispecies atmospheric profiling by high-resolution ultra-wideband laser heterodyne radiometry

理解环境系统越来越需要同时在一系列空间和时间尺度上表征多种化学和动态过程的测量。卫星遥感提供全球大气观测，但空间和时间覆盖范围有限，特别是低层大气和极地区域。地面仪器或部署在空中/亚轨道平台上的仪器可提供更高的空间（水平/垂直）和时间分辨率，这对于描述局地和区域尺度以及具有日变率的过程至关重要。许多与气候变化、臭氧层恢复、城市污染和地球科学/火山学相关的大气微量气体、气溶胶和云可以利用其独特的红外光谱特征进行测量，特别是在大气“窗口”区域（8-12微米）。虽然傅里叶变换光谱仪（FTS）提供了足够的宽带、多路频率覆盖的红外观测，以进一步了解关键的大气参数和过程，但高分辨率系统的复杂性、尺寸/质量、有限的鲁棒性、可靠性问题和成本限制了它们的广泛部署。激光外差辐射计（LHRs）是一种集高光谱分辨率、高空间分辨率、高灵敏度和体积小于一体的被动遥感仪器。一种覆盖大气“窗口”光谱区域（8-12微米）的超宽带激光外差辐射计（UB-LHR）现在有望提供高分辨率FTS的测量性能，但它是一种更小、更坚固、成本更低的仪器。该提案旨在在实验室中表征超宽带LHR （UB-LHR）的性能，该超宽带LHR首次结合了通过与普林斯顿大学合作获得的宽可调谐外腔量子级联激光器。虽然LHR测量原理已经建立，但改变到一个完全不同的激光源是一个根本性的背离，需要进行概念验证工作。UB-LHR的能力将通过地面测量被动大气发射和通过大气传输的红外太阳辐射来证明，这些辐射直接来自太阳或从月球反射（月球掩星），用于夜间/极地冬季观测。该仪器的性能将与世界上最高分辨率的商用FTS相抗衡。从这些测量结果中，可以通过对压力和温度相关的吸收线形状的反演，获得一系列微量气体种类垂直分布的信息。预计所有目标物种所需的测量时间将在10分钟或更短，从而可以观测到涉及O3和H2O的高动态现象，例如在对流层上层-平流层下层（UTLS）区域。

Understanding environmental systems increasingly requires measurements that simultaneously characterise multiple chemical and dynamical processes on a range of spatial and temporal scales. Satellite remote sensing provides global atmospheric observations but has limited spatial and temporal coverage, in particular for the lower atmosphere and polar regions. An instrument on the ground or deployed on an aerial/sub-orbital platform provides the higher spatial (horizontal/vertical) and temporal resolution that is essential for characterising processes on local and regional scales and with diurnal variability. Many atmospheric trace gases, aerosols, and clouds of relevance to climate change, ozone layer recovery, urban pollution, and Earth sciences/volcanology can be measured using their unique infrared spectral signatures in particular in the atmospheric 'window' region, 8-12 microns. While Fourier transform spectrometers (FTS's) provide infrared observations with sufficiently broadband, multiplex frequency coverage to further our understanding of key atmospheric parameters and processes the complexity, size/mass, limited robustness, reliability issues, and cost of high-resolution systems limit their wider deployment. Laser heterodyne radiometers (LHRs) are passive remote sensing instruments which combine high spectral resolution, high spatial resolution, high sensitivity, and compact size. An ultra-wideband laser heterodyne radiometer (UB-LHR) covering the atmospheric 'window' spectral region, 8-12 microns, now promises to offer the measurement performance of high-resolution FTS but in a smaller, more robust, and lower cost instrument. This proposal aims to characterise in the laboratory the performance of an ultra-wideband LHR (UB-LHR) incorporating for the first time a widely-tunable external-cavity quantum cascade laser obtained through collaboration with Princeton University. Although the LHR measurement principle is established, changing to a substantially-different laser source is a radical departure that requires proof-of-concept work. UB-LHR capabilities will be demonstrated through measurements from the ground of both passive atmospheric emission and infrared solar radiation transmitted through the atmosphere, directly from the sun or reflected from the moon (lunar occultation) for night-time/polar winter observations. The instrument performance will be pitched against the World's highest resolution, commercially-available FTS. From these measurements information about the vertical distribution of a range of trace gas species may be retrieved from inverting the pressure- and temperature- dependent absorption line shapes . It is anticipated that the measurement time required for all the target species will be ten minutes or less, allowing observation of highly dynamic phenomena involving O3 and H2O, e.g. in the upper troposphere-lower stratosphere (UTLS) region.