Development of Measurement System of Water Vapor Fluctuation using a Far Infrared Absorption Band in Building Canyon

涡动相关法是估算复杂建筑峡谷内潜热传递的最有效方法。为了应用该方法，必须测量比湿的波动。在本研究中，一个红外线湿度计与光纤通过使用6.3微米的吸收带的水蒸气是新设计的。在波长范围内，测量对太阳辐射和来自周围环境的红外辐射不敏感。测量路径中的平均比湿的波动由基于比尔定律的透射率测量获得。为了尽量减少湿度计对测量的干扰，湿度计分为光源块和测量块两个部分。在一个试验箱中，对湿度计的静态特性进行了测试，这些静态特性是比湿度（5-20 g/kg）、空气温度（283-303 K）和光程（150-250 nm）的函数。与光学结露指示器相比，其分辨率优于0.1g/kg。还通过在干燥试验箱中间歇供应湿空气来检查动态响应。对实验结果进行频谱分析得到的主频率与受控电源频率一致，小于10 Hz。湿度计最后被更换用于现场测量。它们将在几种类型的建筑峡谷中进行。

An eddy correlation method is most useful for estimating the latent heat transfer in the complex building canyons. In order to apply this method, it is necessary to measure the fluctuation of specific humidity. In the present study, an infrared hygrometer with optical fiber by using 6.3 mum absorption band of water vapor is newly designed. In the wavelength range, the measurements are insensitive to solar radiation and infrared radiation from the surroundings. The fluctuation of the averaged specific humidity in the measuring path is obtained from the transmittance measurement based on Beer's law. In order to minimize the disturbance of the hygrometer on the measurement, the hygrometer is divided into two parts called a light source block and a measurement block. These blocks are connected by an optical fiber cable.The static characteristics of the hygrometer were examined in a test chamber as a function of the specific humidity (5-20 g/kg), the air temperature (283-303 K) and the path length (150-250 nm). The resolution better than 0.1 g/kg was obtained comparing with an optical dew indicator. The dynamic responses were also checked by the intermittent supply of wet air in the dry test chamber. The dominant frequency obtained from the spectral analysis of the experimental results agreed with the controlled supply frequency less than 10 Hz. The hygrometer was finally changed for the field measurements. They will be performed in several types of building canyons.