The water vapour continuum in near-infrared windows - Current understanding and prospects for its inclusion in spectroscopic databases
The water vapour continuum in near-infrared windows - Current understanding and prospects for its inclusion in spectroscopic databases
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近红外窗口中的水蒸气连续体 - 当前的理解和将其纳入光谱数据库的前景
DOI：
10.1016/j.jms.2016.04.011
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发表时间：
2016
影响因子：
1.4
通讯作者：
Shine K
中科院分区：
文献类型：
--
作者：
Shine K
光谱目录，如GEISA和HITRAN，还不包括遍及可见光、红外和微波光谱区域的水蒸气连续体的信息。部分原因是，在某些光谱区域，在接近地球大气层的条件下，很少有实验室测量；因此，对连续吸收特性的认识仍在不断发展。在近红外和可见光领域尤其如此，近年来人们对这些领域重新产生了兴趣和活动。在本文中，我们提出了一个关键的审查，重点是最近在两个近红外窗口区域的实验室测量（集中在4700和6300厘米−1），并包括参考集中在2600厘米−1的窗口，在那里有更多的测量报告。很少有可用的测量方法，使用傅立叶变换光谱（FTS），腔衰荡光谱，光反馈腔增强激光光谱，以及在非常狭窄的区域，量热干涉测量。这些系统有不同的优点和缺点。傅里叶变换光谱可以测量这些窗口和邻近窗口的连续统；相比之下，腔激光技术受限于较少的波数，但具有更高的固有灵敏度。现有的结果呈现了连续体吸收特征的不同观点，在这些窗口的核心中，连续体强度的差异超过了10倍。在单个窗口中，水汽自连续体的温度依赖性在允许进行分析的少数几组测量值中差别很大。现有数据还表明，不同近红外窗口间的温度依赖性存在显著差异。这些开创性的测量为进一步的测量提供了动力。现有技术的改进和/或扩展将有助于对连续统进行全面表征——例如，我们报告了使用超连续统激光源耦合到FTS的水蒸气自连续统的试点测量。这种改进，以及其他实验室的额外测量和分析，将使水汽连续体能够列入未来的光谱数据库，从而能够对大气的辐射特性进行更可靠的正演模拟。它也将允许对连续吸收的根本原因或原因的不同理论描述作出更有信心的评估。
Spectroscopic catalogues, such as GEISA and HITRAN, do not yet include information on the water vapour continuum that pervades visible, infrared and microwave spectral regions. This is partly because, in some spectral regions, there are rather few laboratory measurements in conditions close to those in the Earth’s atmosphere; hence understanding of the characteristics of the continuum absorption is still emerging. This is particularly so in the near-infrared and visible, where there has been renewed interest and activity in recent years. In this paper we present a critical review focusing on recent laboratory measurements in two near-infrared window regions (centred on 4700 and 6300 cm−1) and include reference to the window centred on 2600 cm−1where more measurements have been reported. The rather few available measurements, have used Fourier transform spectroscopy (FTS), cavity ring down spectroscopy, optical-feedback – cavity enhanced laser spectroscopy and, in very narrow regions, calorimetric interferometry. These systems have different advantages and disadvantages. Fourier Transform Spectroscopy can measure the continuum across both these and neighbouring windows; by contrast, the cavity laser techniques are limited to fewer wavenumbers, but have a much higher inherent sensitivity. The available results present a diverse view of the characteristics of continuum absorption, with differences in continuum strength exceeding a factor of 10 in the cores of these windows. In individual windows, the temperature dependence of the water vapour self-continuum differs significantly in the few sets of measurements that allow an analysis. The available data also indicate that the temperature dependence differs significantly between different near-infrared windows. These pioneering measurements provide an impetus for further measurements. Improvements and/or extensions in existing techniques would aid progress to a full characterisation of the continuum – as an example, we report pilot measurements of the water vapour self-continuum using a supercontinuum laser source coupled to an FTS. Such improvements, as well as additional measurements and analyses in other laboratories, would enable the inclusion of the water vapour continuum in future spectroscopic databases, and therefore allow for a more reliable forward modelling of the radiative properties of the atmosphere. It would also allow a more confident assessment of different theoretical descriptions of the underlying cause or causes of continuum absorption.