Observation of Urban Atmospheric Boundary Layer Structure with Doppler Lidars

The urban boundary layer is one of the least understood aspects of the atmospheric boundary layer because of its complex features and difficulty in observation. A unique set of data was collected through the intensive observation of turbulent flow in Tokyo, Japan, on 21 December 2017. Two Doppler lidars were used during this observation. One of them is the Large-scale Coherent Doppler Lidar which is capable of measuring the line-of-sight velocity up to a distance of 30 km with an eye-safe wavelength of 1.5 µm. This lidar was operated in a pointing model at an angle of 2.3 degrees downward to the observation site from about 10 km away. The range resolution was 75 m and temporal resolution was 2 seconds. Another compact optical-fiber Doppler lidar was allocated at the observation site to observe the vertical wind structure in the urban boundary layer. The lidar was operated in Plan Position Indicator (PPI) mode in the morning section and Range Height Indicator (RHI) mode in the afternoon section individually. The PPI sector scan swept 180 degrees on an elevation angle of 45 degrees in a 3 minutes cycle. On the other hand, the RHI scanned over any elevation range from -4 to +90 degrees with a scanning speed of 1 degree per second. At the same time, toy balloons were release to the sky from the observation site every 30 seconds; the balloons’ trajectories were captured by 13 digital cameras and the advection velocity of them was computed by image processing. This paper will report the primary analysis of lidar observations and compare result with balloon observations.