Acoustic tomography and conventional meteorological measurements over heterogeneous surfaces

Summary

Conventional micro-meteorological measuring methods are not particularly suitable for the investigation of the energy exchange under heterogeneous surface conditions. To consider the influence of the different surface properties, area-covered and spatially averaged meteorological measurements in combination with highly resolved simulations are necessary. In this context, the method of acoustic travel time tomography is introduced to provide information about the horizontal temperature and wind field.

To check the applicability of the tomographic method for this problem and to provide data for the model initialisation a field experiment was carried out.

The tomographic system and conventional meteorological equipment were utilised inside the investigation area with an extension of several hundred meters (300×700 m²), which was arranged over areas with different surface properties: grassland and bare soil.

The results of the field experiment show that differences between the measuring systems (in-situ and remote sensing) exist and the heterogeneity of the underlying surface is visible in the near surface temperature and wind field at a scale, which can be resolved with highly resolved numerical models. Depending on the incoming solar radiation and the local advection regional distinctions in the air temperature and wind field as well as in the vertical sensible heat fluxes were observed.

The investigations demonstrate that the sensitivity of the acoustic tomography is sufficient to verify gradients in the meteorological fields even when the horizontal differences in sensible heat flux are small.