Short wavelength absorption by water vapour

大气中两个主要的辐射传输过程是吸收入射太阳光和吸收出射辐射，这就是通常所说的温室效应。尽管水的旋转振动光谱在波长上有很大的不同，但它既是太阳光的主要吸收者，也是主要的温室气体。因此，水的自转振动光谱在一定程度上是大气过程中最重要的光谱。全球辐射传输和地球能量收支的模型以及更详细的研究，例如通过遥感恢复柱密度和其他物种的轮廓，都需要准确的水光谱知识。当然，水的光谱得到了很好的研究，但仍然是一个挑战：它非常广泛、复杂(在高分辨率下没有规则的结构)，而且对大气具有重要意义的各个跃迁的强度具有巨大的动态范围。现代遥感卫星的要求需要高精度的水线强度，以监测水柱，并由于水的吸收如此普遍，以至于其水线干扰其他检索，因此用于探测一长串痕量物种。在最好的情况下，未能准确地建立吸水量模型会给反演带来一个主要的误差来源，在最坏的情况下，可能意味着它们完全失败，从而严重降低远程观测的有效性。许多物种，如HONO、OClO、NO_2、SO_2、O_3、BrO、HCHO、O_4、IO和乙二醛都是用它们的紫外光谱监测的。从最近的大气研究中可以明显看出，准确地表示近紫外线中的水吸收对于准确地提取它们是必不可少的。找回水柱是一项重大而重要的活动。在近紫外线下恢复水柱具有显著的优势，因为地球在这些波长上以更均匀的方式反射阳光，而较弱的吸收意味着阻碍在潮湿大气中确定可靠水柱的光学厚度效应在很大程度上被消除了。然而，精确的检索依赖于准确的实验室数据，而这些数据在很大程度上是缺乏的。正在飞行或计划中的卫星，如美国国家航空航天局的首个地球冒险仪器类任务TEMPO(对流层排放：监测污染)任务、欧空局的哨兵系列任务和韩国的GEMS(地球静止环境货币化卫星)任务，将在近紫外线波段以高空间分辨率分析空气的化学成分。所有这些任务都将需要高质量的水实验室数据，其波长范围延伸至近紫外光。目前根本没有这些数据：该区域没有直接、高分辨率的实验室或大气测量水蒸气光谱，HITRAN等大气数据库也没有这方面的相关信息。这些数据将使用第一原理量子力学技术产生，这些技术已经成功地应用于较长波长的水蒸气和其他关键大气物种的吸收。在可能的情况下，将使用实验室测量来调整吸收特征的位置。所产生的线表将提供给在近紫外线中监测地球大气的主要小组，保存在数据储存库中，并提供给HITRAN等数据库。

The two dominant radiative transport processes in our atmosphere are absorption of incoming sunlight, and the absorption of outgoing radiation in what is commonly called the greenhouse effect. Despite occurring at significantly different wavelengths, the rotation-vibration spectrum of water is both the dominant absorber of sunlight and the major greenhouse gas. Thus the rotation-vibration spectrum of water is, by some distance, the single most important spectrum for atmospheric processes. Accurate knowledge of water spectra is required for models of global radiative transport and the earth's energy budget and for more detailed studies such as retrievals of column densities and profiles of other species by remote sensing. The spectrum of water is of course very well studied but remains a challenge: it is very extended, complicated (with no regular structure at high resolution) and the intensities of individual atmospherically important transitions have a huge dynamic range. The demands of modern remote sensing satellites require water line intensities with high accuracy for both monitoring water columns and, because water absorption is so ubiquitous that its lines interferes other retrievals, for detection of a long list of trace species. Failure to model water absorptions accurately at best introduces a major source of error into retrievals and at worst can mean they fail altogether thus severely degrading the usefulness of remote observations. Many species, such as HONO, OClO, NO2, SO2, O3, BrO, HCHO, O4, IO and Glyoxal are monitored using their ultraviolet (UV) spectrum. It has become apparent from recent atmospheric studies that accurate representation of water absorption in the near UV is essential for their accurate retrieval. Retrieval of water columns is a major and important activity. Retrieval of water columns in the near UV has significant advantages since the Earth reflects sunlight in a much more uniform fashion at these wavelengths and the weaker absorption means that optical thickness effects which prevent the determination of reliable water columns in humid atmospheres are largely eliminated. However, precise retrievals rely on the availability of accurate laboratory data which are largely lacking. Satellites flying or planned such as NASA's first Earth Venture Instrument Class mission TEMPO (Tropospheric Emissions: Monitoring Pollution) mission, ESA's Sentinal series and Korea's GEMS (geostationary environmental monetaring satellite) mission will analyse the chemical composition of air with high spatial resolution at near UV wavelengths. All these missions will require high quality laboratory data for water over an extended wavelength range stretching into the near-UV. At present these data are simply not available: there are no direct, high-resolution laboratory or atmospheric measurements of water vapour spectra in the region, and atmospheric database such as HITRAN, contain no relevant information on it.The aim of this proposal is to provide comprehensive and accurate data on water absorption at short wavelengths. These data will be generated using techniques of first principle quantum mechanics that have been successfully applied to both absorption by water vapour at longer wavelengths and other key atmospheric species. Where possible the positions of absorption features will be adjusted using laboratory measurements. The resulting line lists will be made available to key groups involved monitoring the Earth's atmosphere in the near UV, placed in data depositories and made available to databases such as HITRAN.