Abstract. This work describes the latest design, calibration and application of a near-infrared laser diode-based photoacoustic (PA) hygrometer, developed for total water content measurement in simulated atmospheric freezing precipitation and high ice water content conditions with relevance in fundamental icing research, as well as aviation testing and certification. The single-wavelength and single-pass PA absorption cell is calibrated for molar water vapor fractions with a two-pressure humidity generator integrated into the instrument. Laboratory calibration showed an estimated measurement accuracy better than 3.3 % in the water vapor mole fraction range of 510–12,360 ppm (5 % from 250–21,200 ppm) with a theoretical limit of detection (3 sigma) of 3.2 ppm. The hygrometer is examined in combination with a basic isokinetic evaporator probe (IKP) and sampling system designed for icing wind tunnel application, for which a general description of total condensed water content (CWC) measurement and uncertainties are presented. Despite the current limitation of the IKP to a hydrometeor mass flux below 90 g m⁻² s⁻¹, a CWC measurement accuracy better than 20 % is achieved by the instrument above a CWC of 0.14 g m⁻³ in cold air (−30 °C) with suitable background humidity measurement. Results of a comparison to the Cranfield University IKP instrument in freezing drizzle and rain show a CWC agreement of the two instruments within 20 %, which demonstrates the potential of PA hygrometers for water content measurement in atmospheric icing conditions.

中文翻译：

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用于结冰风洞水分测量的光声湿度计：设计，分析和比较

摘要。这项工作描述了一种基于近红外激光二极管的光声（PA）湿度计的最新设计，校准和应用，该湿度计旨在用于模拟大气冻结降水和高冰水含量条件下的总含水量测量，与基础结冰研究相关。以及航空测试和认证。使用集成在仪器中的双压湿度发生器，对单波长和单程PA吸收池进行校准，以测量水蒸气摩尔分数。实验室校准显示，在510–12,360 ppm的水蒸气摩尔分数范围内（250％至21,200 ppm的5％），估计的测量精度优于3.3％，理论检测限（3 sigma）为3.2 ppm。结合基本的等速蒸发器探头（IKP）和为结冰风洞应用而设计的采样系统，对湿度计进行了检查，并给出了总冷凝水含量（CWC）测量的总体描述和不确定性。尽管IKP目前受限于水汽流质量流量低于90 g m⁻²  s ^-1，在冷空气（−30°C）下，通过适当的背景湿度测量，仪器在0.14 g m ^-3的CWC之上，可实现优于20％的CWC测量精度。与克兰菲尔德大学IKP仪器在冻毛毛雨和雨中的比较结果表明，这两种仪器的CWC吻合度在20％以内，这证明了PA湿度计在大气结冰条件下测量水分的潜力。