The feasibility of water vapor sounding of the cloudy boundary layer using a differential absorption radar technique
The feasibility of water vapor sounding of the cloudy boundary layer using a differential absorption radar technique
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DOI：
10.5194/amt-8-3631-2015
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发表时间：
2015-09
影响因子：
3.8
通讯作者：
M. Lebsock;Kentaroh Suzuki;L. Millán;P. Kalmus
中科院分区：
文献类型：
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作者：
M. Lebsock;Kentaroh Suzuki;L. Millán;P. Kalmus
抽象的。通过将雷达仪器模拟器应用于大涡模拟（LES），评估了差分吸收雷达（DAR）对多云边界层内水蒸气进行星载远程分析的可行性。 183 GHz 水蒸气吸收线附近的频率衰减太强，无法穿透边界层中普遍存在的大量水蒸气浓度。然而，研究表明，水蒸气吸收连续谱中和吸收线翼上的 140 至 170 GHz 之间的较低频率，其衰减效率低于吸收线中心附近的频率，但仍然具有足够的气体衰减光谱变化来执行探测。高分辨率 LES 允许评估由于热力学和动态变量在小于仪器视场的尺度上的自然变化而导致的方法中的潜在不确定性。建议使用 (160, 170) GHz 频率对，以最大程度地最大化蒸汽剖面信号，同时最大限度地减少由于目标消光特性中不需要的光谱变化而产生的噪声。导出的水蒸气的精度被量化为距离分辨率和仪器精度的函数。假设垂直观测空间尺度为 500 m，水平半高全宽 (FWHM) 为 750 m，在雷达反射率精度为 0.16 dBZ 的情况下，层积云场景的测量精度可达到 1 g m−3，积云场景的测量精度可达到 3 g m−3。在这些相同的空间尺度上，柱水蒸气 (CWV) 的预期精度可达到 0.5 至 2 kg m−2 之间。采样效率被量化为雷达灵敏度的函数。由于目标消光特性的自然变化而导致的 CWV 平均偏差不超过 0.25 kg m−2。相对于自然变化引起的偏差，由于温度和压力分布的不确定性而导致的潜在偏差可以忽略不计。假设最小可检测信号为−35 dBZ，则将对层积云（积云）大气边界层范围箱的 40%（21.9%）进行采样。模拟的表面反射率始终大于-5 dBZ，这意味着DAR技术可以以优于1 km的空间分辨率对副热带边界层中的CWV进行近空间连续观测。
Abstract. The feasibility of differential absorption radar (DAR) for the spaceborne remote profiling of water vapor within the cloudy boundary layer is assessed by applying a radar instrument simulator to large eddy simulations (LES). Frequencies near the 183 GHz water vapor absorption line attenuate too strongly to penetrate the large vapor concentrations that are ubiquitous in the boundary layer. However it is shown that lower frequencies between 140 and 170 GHz in the water vapor absorption continuum and on the wings of the absorption line, which are attenuated less efficiently than those near the line center, still have sufficient spectral variation of gaseous attenuation to perform sounding. The high resolution LES allow for assessment of the potential uncertainty in the method due to natural variability in thermodynamic and dynamic variables on scales smaller than the instrument field of view. The (160, 170) GHz frequency pair is suggested to best maximize signal for vapor profiling while minimizing noise due to undesired spectral variation in the target extinction properties. Precision in the derived water vapor is quantified as a function of the range resolution and the instrument precision. Assuming an observational spatial scale of 500 m vertical and 750 m full width at half maximum (FWHM) horizontal, measurement precision better that 1 g m−3 is achievable for stratocumulus scenes and 3 g m−3 for cumulus scenes given precision in radar reflectivity of 0.16 dBZ. Expected precision in the column water vapor (CWV) is achievable between 0.5 and 2 kg m−2 on these same spatial scales. Sampling efficiency is quantified as a function of radar sensitivity. Mean biases in CWV due to natural variability in the target extinction properties do not exceed 0.25 kg m−2. Potential biases due to uncertainty in the temperature and pressure profile are negligible relative to those resulting from natural variability. Assuming a −35 dBZ minimum detectable signal, 40 %(21.9 %) of stratocumulus(cumulus) atmospheric boundary layer range bins would be sampled. Simulated surface reflectivities are always greater than −5 dBZ, which implies the DAR technique could provide near spatially continuous observation of the CWV in subtropical boundary layers at a spatial resolution better than 1 km.