3D wind profiling from the surface to the top of the urban boundary layer with Doppler lidars

Urban structures increase turbulence within the atmospheric boundary layer (ABL) due to increased surface roughness and create channel effects within the urban canopy that cannot be fully captured by a single measurement technique. Furthermore, operational measurements within urban structures are difficult due to limited space and nearby objects.

Doppler lidars are a preferred remote sensing tool for observing the wind profile in the ABL, but they miss either the urban canopy or the upper ABL. Pulsed Doppler lidars (PDL) are typically sensitive enough to reach the top of the ABL, but they leave an unobserved gap in the lower 50 m and cannot reliably resolve wind gradients within the lowest range gates. Continuous wave Doppler lidars (CDL) are typically limited to a maximum height of 200 m because the range is achieved by focusing the beam. To observe the entire wind profile from the surface to the top of the ABL, we deploy a PDL and a CDL in combination. For retrieving vertical 3D wind profiles, both lidars perform conical scans (VAD) around a vertical axis with a narrow 10° zenith angle, which reduces the diverting of the beams and separation of the measuring volumes along the scan. This also allows for measurements in complex terrains with obstacles like high buildings and trees.

We present measurements of the 3D wind profile obtained with a combination of PDL and CDL. Both lidars are in very good agreement with mast measurements. Results from measurements in a street canyon at an urban site (Hamburg) are presented.