The Spatial Structure of RASS Echoes

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  • 1 Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia
  • | 2 Radio Atmospheric Science Center, Kyoto University, Uji, Kyoto, Japan
  • | 3 Environmental Technology Laboratory, NOAA/ERL, Boulder, Colorado
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Abstract

An experiment to observe the spatial distribution of radio acoustic sounding system (RASS) echo intensity and Doppler shift using the MU radar is described. Various transmitting configurations are used to confirm that the RASS signal is focused onto a diffraction limited spot approximately the size of the transmitting antenna, except when a very small transmitting array is used where turbulence acting on the acoustic wave smears the spot. The signal fades away from the central spot with values about 6-10 dB lower in intensity next to the main spot. Significant gradients of Doppler shift across the radar antenna are seen in the lower height ranges. This may result in errors as large as a degree in the RASS virtual temperature estimates when large radar antennas and a single acoustic source are used.

Abstract

An experiment to observe the spatial distribution of radio acoustic sounding system (RASS) echo intensity and Doppler shift using the MU radar is described. Various transmitting configurations are used to confirm that the RASS signal is focused onto a diffraction limited spot approximately the size of the transmitting antenna, except when a very small transmitting array is used where turbulence acting on the acoustic wave smears the spot. The signal fades away from the central spot with values about 6-10 dB lower in intensity next to the main spot. Significant gradients of Doppler shift across the radar antenna are seen in the lower height ranges. This may result in errors as large as a degree in the RASS virtual temperature estimates when large radar antennas and a single acoustic source are used.

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