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潜热传递最有效的方法。为了应用该方法，有必要测量比湿度的波动。本文设计了一种利用6.3 μ m水汽吸收带的光纤红外湿度计。在波长范围内，测量对太阳辐射和周围的红外辐射不敏感。根据比尔定律对透光率进行测量，得到了平均比湿度在测量路径上的波动。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部分。这些块通过光纤连接起来。湿度计的静态特性随比湿度（5-20 g/kg）、空气温度（283-303 K）和路径长度（150-250 nm）的变化而变化。与光学露珠指示器相比，分辨率优于0.1 g/kg。通过在干燥试验室内间歇性地提供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导频率与控制电源频率小于10hz一致。最后，湿度计被改为现场测量。他们将在几种类型的建筑峡谷中表演。

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.