Estimation of sensible heat flux in an urban area with scintillometer

闪烁计是新近发展起来的一种利用双偏振激光束闪烁来测量感热通量的仪器。由梁强度的涨落导出了温度的结构函数，由双梁的相关性导出了能量耗散率，在Monin-Obukhov相似性假设下，由这两个湍流参数估算了光束路径上的感热通量，并给出了一些经验公式。它具有测量路径平均感热通量容易的优点，但测量的前提条件，特别是在城市的情况下，还没有这么清楚。本研究利用涡度计对流经建筑区的河流水面、城市公园草地、水田、植被覆盖的阶梯式屋顶花园等地表进行了感热通量的观测验证，并与涡度相关法的通量进行了比较。阐明了热辐射计的测量精度和测量条件的限制，为检验热辐射计用于垂直建筑物墙面显热通量测量的可行性，还设计了一种利用反射镜折射改变光路的装置，反射镜在发射机和接收机之间的位置是很重要的。在发射机后、接收机前的情况下，镜面折射对通量测量没有影响。而V形光路，即反射镜位于光路的中部，激光强度的波动变得很不稳定，不能在任何入射角下测量。

Scintillometer is newly developed instrument for measuring the sensible heat flux by detecting scintillation of twin polarized laser beams. Structure function of temperature is derived from fluctuation of beam strength, and energy dissipation rate is derived from correlation of twin beam.Sensible heat flux over beam path is estimated from these two parameters of turbulence assuming with the Monin-Obukhov Similarity with some empirical formulas. It has the advantage of measuring path averaged sensible heat flux easily, but prerequisite for measurement, especially in the case of urban area, has not been so clear yet. In this study, observations for verification of sensible heat flux by scintillometer were performed in various kinds of surface, for example river water surface running through built-up area, grassland surface in urban park, paddy field, vegetated stepwise roof-garden, and so on. With the comparison of flux by eddy correlation method, accuracy of scintillometer and some limits of measuring condition were clarified.In order to check the possibility of application of scintillometer to measure sensible heat flux from vertical building wall surface, the apparatus for path change by mirror refraction are also devised.The position of the mirror between transmitter and receiver is important. In the case of just after transmitter and just before receiver, there was no influence of mirror refraction on flux measurement. But V-shape path, that is mirror was located at the middle part of laser path, fluctuation of laser strength become rather unstable and could not measure in any incident angle.