Mobile Urban Turbulent Flux Measurements

Ultrasonic anemometers have been the cornerstone in observing momentum, heat and scalar fluxes near the surface. Urban life, between tall and dense buildings has raised questions about the usefulness of flux observations at the surface. The strict regulations for weather stations misrepresent the effects of the urban environment. Therefore, we are faced with the conundrum of how to take flux measurements higher up in the urban canopy, where the effect of the quasi-surface urban parameters are still representative to the atmospheric boundary layer processes. While vertical soundings with gradient methods and aerial observations can give us flux measurements, they are almost always too far from the urban environment both horizontally and vertically.

A series of experiments combining mobile and stationary observations employing sonic-anemometer-equipped bicycle and drone were conducted. Along an urban river, a bicycle is used in a one-dimensional path to assess the quality of the flux measurements of a moving observer compared with two static observers. A drone was flown in three-dimensional (3D) space to observe 3D turbulent fluxes. Taylor’s hypothesis of frozen turbulence is what provides insight into vertical transport. This research investigates the extent to which Taylor’s hypothesis, within reason, holds true for a moving observer, while also assessing the departure from ground truth and the possibility of correcting these signals.