RESUMEN
The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed.
Asunto(s)
Acústica , Presión Atmosférica , Gravitación , Modelos Teóricos , Procesamiento de Señales Asistido por Computador , Sonido , Viento , Movimiento (Física) , Espectrografía del Sonido , Factores de Tiempo , Tomografía/métodosRESUMEN
Mesoscale wind speed and temperature fluctuations with periods from 1 min to a few hours significantly affect temporal variability and turbulent regime of the stable atmospheric boundary layer (ABL). Their statistical characteristics are still poorly understood, although the knowledge of such statistics is required when modeling sound propagation through the stable ABL. Several field experiments have been conducted to study the influence of mesoscale wind speed fluctuations on acoustic pulse propagation through the stable ABL. Some results of these experiments are described in this paper. A special acoustic source was used to generate acoustic pulses by the detonation of an air-propane mixture with a repetition period 30 s. The mean wind speed and temperature profiles were continuously measured by Doppler sodar and temperature profiler, whereas mesoscale wind fluctuations were measured by anemometers placed on a 56-m mast. From the measurements of the pulse travel time fluctuations at different distances from the source, the statistical characteristics of the mesoscale wind fluctuations, such as frequency spectra, coherences, horizontal phase speeds and scales, have been obtained. Some of the obtained results are interpreted with the use of a recently developed model for the internal wave spectrum in a stably stratified atmosphere.