Quality and representability of mobile measurements for local climatological research

Temperature recordings from a moving vehicle are frequently used in microclimatological research. This work aims at investigating three aspects of the quality and the representability of mobile-recorded temperature data: the displacement of air near the car's front; the inertia of the sensors which hinders the accurate recording of fast fluctuations, and how good temperature profiles obtained above a road correspond to temperature profiles of areas adjacent to the road. 72 Air parcels undergo a slight vertical deflection close to the car's front compared to their undisturbed level farther away from the car. Sonic anemometer measurements while the car is at rest were done to estimate the displacement of air parcels at the car's front. The results indicate small total vertical deflection at sensor position. The time behaviour of two different thermocouples was estimated using spectral analysis. At low frequencies the effect of the sensors' time constant is negligible, but inereases above 0.01 Hz. The spectra are corrected for the influenee of the time constant and compared with a spectrum of a simultaneously obtained sonic anemometer measurement. The differenees are small at the lowest frequencies but increase with inereasing frequencies. Measurements on foot along transects perpendicular to a road were done to estimate the representability of mobile-collected temperature data and the influence of the road. The measurements carried out during autumn showed no substantial influence caused by the road. There may be, however, marked differences in the near-ground temperature distribution on both sides of the road. The ground's influence diminishes with increasing sensor height.