Sensitivity analysis of space-based water vapor differential absorption lidar at 823 nm

R. Barton-Grimley, A. Nehrir
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Abstract

Measurements of water vapor are important for understanding the hydrological cycle, the thermodynamic structure of the lower troposphere, and broader atmospheric circulation. Subsequently, many scientific communities have emphasized a need for high-accuracy and spatial resolution profiles of water vapor within and above the planetary boundary layer (PBL). Advancements in lidar technologies at the NASA Langley Research Center are ongoing to enable the first space-based water vapor differential absorption lidar (DIAL) that can provide high-accuracy and vertical resolution retrievals of moisture in the PBL and through the mid-troposphere. The performance of this space-based DIAL is assessed here for sensitivity throughout the troposphere and globally with representative canonical cases of water vapor and aerosol loading. The specific humidity retrieval sensitivity to systematic and random errors is assessed, and measurement resolutions and capabilities are provided. We show that tunable operation along the side of the 823-nm absorption line allows for the optimization of the lower-tropospheric water vapor retrievals across different meteorological regimes and latitudes and provides the operational flexibility needed to dynamically optimize random errors for different scientific applications. The analysis presented here suggests that baseline and threshold systematic error requirements of <1.5% and <2.5%, respectively, are achievable. Random error is shown to dominate the retrieval, with errors on the order of 5% within the PBL being achievable with 300-m vertical 50-km horizontal resolutions over open ocean and on the order of 10%–15% over high-albedo surfaces. The flexibility of the DIAL method to trade retrieval precision for spatial resolution is shown, highlighting its strengths over passive techniques to tailor retrievals to different scientific applications. Combined, the total error budget demonstrated here indicates a high impact for space-based DIAL, with technologies being advanced for space missions within the next 5–10 years.
823 纳米波长天基水汽差分吸收激光雷达灵敏度分析
水汽测量对于了解水文循环、对流层下部的热力学结构和更广泛的大气环流非常重要。因此,许多科学界都强调需要对行星边界层(PBL)内部和上方的水汽进行高精度和空间分辨率的剖面测量。美国国家航空航天局兰利研究中心的激光雷达技术正在不断进步,以实现首个天基水汽差分吸收激光雷达(DIAL),该激光雷达可对行星边界层和对流层中层的水汽进行高精度和垂直分辨率的检索。本文评估了这一天基 DIAL 在整个对流层和全球范围内对水汽和气溶胶负荷的代表性典型案例的灵敏度。评估了特定湿度检索对系统和随机误差的灵敏度,并提供了测量分辨率和能力。我们表明,沿 823-nm 吸收线一侧的可调操作允许优化不同气象制度和纬度的低对流层水汽检索,并提供了为不同科学应用动态优化随机误差所需的操作灵活性。本文的分析表明,基线和阈值系统误差要求分别为<1.5%和<2.5%是可以实现的。随机误差在检索中占主导地位,在开阔海洋上,垂直分辨率为300米、水平分辨率为50千米的PBL内可实现5%的误差,在高地层表面可实现10%-15%的误差。DIAL 方法可以灵活地以检索精度换取空间分辨率,与被动技术相比,它在根据不同的科学应用进行检索方面更具优势。综合来看,本文所展示的总误差预算表明,天基 DIAL 对未来 5-10 年内的空间任务具有重大影响,其技术也将不断进步。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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