Estimation of sensible heat flux in an urban area with scintillometer

闪烁仪是新近发展起来的一种通过探测双偏振激光的闪烁来测量显热通量的仪器。温度的结构函数由束流强度的起伏得到，能量耗散率由双光束的关联得到，根据这两个湍流参数，采用Monin-Obukhov相似假设和一些经验公式，估算出光路上的感热通量。它具有易于测量路径平均感热通量的优点，但测量的前提条件，特别是在城市地区的情况下，还不是很明确。在本研究中，利用闪烁仪对城区河流水面、城市公园草地、水田、台阶式屋顶花园等不同地表的感热通量进行了观测验证。通过对比涡旋相关法测量的感热通量，明确了闪烁仪的测量精度和测量条件的局限性。为了验证闪烁仪应用于垂直建筑墙面感热通量测量的可行性，设计了镜面折射式光路转换装置。在发射后和接收前的情况下，镜面折射对流量测量没有影响。但V型光路，即反射镜位于激光光路的中间部分，激光强度的波动变得相当不稳定，不能在任何入射角度下进行测量。

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.