The combination of line averaged scintillometer measurements and area averaged acoustic travel time tomography is proposed as a method for remote monitoring of near surface sensible heat fluxes, temperature and wind fields.
Three optical scintillometers (Scintec, SLS-20) were used, which provide as basic output parameters the refractive index structure parameter and the inner scale length of turbulence from which the dissipation rate of turbulent kinetic energy, and the fluxes of sensible heat and momentum are deduced using similarity methods. The procedure of acoustic tomography applies the horizontal propagation of sound waves in the atmospheric surface layer. The state of the crossed atmosphere can be estimated from measurements of travel time of acoustic signals between sources and receivers on different points in a tomographic array. Derivation of area averaged values of the sound speed and furthermore of air temperature results from the inversion of travel time values for all possible acoustic paths. Thereby, the applied straight-ray two-dimensional tomographic model is characterised as a method with small computational requirements and simple handling, especially, for online work.
A field experiment was carried out at the research site Melpitz near Leipzig (Germany) over grassland in autumn 1997. Six sources (compression drivers) and four receivers (microphones) were positioned at an array of 200 m x 260 m on tripods at a height of 2 m and 4.5 m, respectively. The scintillometers were arranged in a triangle with optical path lengths of 100 -120 m and with a path height of 1.70 m. For two sunny days the sensible heat fluxes, estimated with the three scintillometer, were compared with the temperature distributions along and near the optical paths. For the interpretation additionally sonic anemometer and profile measurements are used.