Studies of the aspect sensitivity of polar mesosphere summer echoes using spectral width and spatial correlation methods

The aspect sensitivity of mesospheric scatterers at a frequency of 53.5 MHz is studied during the presence of polar mesosphere summer echoes using simultaneous multi-beam Doppler observations and spaced antenna observations. The height variation of aspect sensitivity throughout the PMSE season is studied by MST radar observations at Andenes in 1999. The highest degree of aspect sensitivity occurs in general in the lower part of a PMSE layer. Studies of the measured total spectral width compared to the beam broadened spectral width show that the spectral width increases as the altitude increases but the spectral width is often dominated by beam broadening especially in the lower part of the PMSE layer at altitudes below of about 85 km. In addition, the theta (s) approach allows direct estimations of the length-to-depth ratio of the scatterers. The relation between aspect sensitivity of the scattered radiation and the average shape of the scatterers (length-to-depth ratio) are discussed..