Medium frequency (MF) radars are typically operated between 2 and 3.5 MHz. With these radars, echoes from the Mesosphere-Lower-Thermosphere can be observed continuously due to partial reflection from relatively sharp boundary between media of different refractive indices. The most common use of MF radars is to measure mesospheric winds in the altitude region of about 60 km to 100 km. There are generally two main methods to measure horizontal winds, which are typically defined by the complexity of the radar and its antenna array:
- The Doppler beam swinging (DBS) method, where a narrow antenna beam is steered sequentially into different, typically oblique, directions. From the line-of-sight velocities of individual beam pointing directions, and assuming homogeneity, the mean vertical and horizontal winds are calculated.
- The spaced antenna (SA) method uses a vertically pointing antenna beam and at least three non-collinear receiving antennas on reception. From the temporal changes of the diffraction pattern on the ground, the horizontal velocity, shape and coherence of the scattering layers are inferred. Such diffraction pattern is obtained from the cross correlation or cross spectra analysis of signals received at the spaced receiving antennas.
From the derived wind fields e.g. wave parameters and energy dissipation rates can be derived. Additionally, the Saura MF radar allows the estimation of electron density by differential absorption and differential phase measurements.
Existing MF radars at IAP:
- W. Singer, P. Hoffmann, G. Kishore Kumar, N. J. Mitchell und V. Matthias, Atmospheric coupling by gravity waves: Climatology of gravity wave activity, mesospheric turbulence and their relations to solar activity, in Climate And Weather of the Sun-Earth System (CAWSES): Highlights from a priority program, Springer, F.-J. Lübken, Dordrecht, The Netherlands, doi:10.1007/978-94-007-4348-9, 2012
- W. Singer, R. Latteck, M. Friedrich, M. Wakabayashi und M. Rapp, Seasonal and solar activity variability of D-region electron density at 69° N, J. Atmos. Solar-Terr. Phys., doi:10.1016/j.jastp.2010.09.012, 2011
- P. Hoffmann, E. Becker, W. Singer und M. Placke, Seasonal variation of mesospheric waves at northern middle and high latitudes, J. Atmos. Solar-Terr. Phys., 72, 1068-1079, doi:10.1016/j.jastp.2010.07.002, 2010
- W. Singer, R. Latteck, D. A. Holdsworth und T. Kristiansen, A new narrow beam MF radar at 3 MHz for studies of the high-latitude middle atmosphere: System description and first results, Proceedings of the 10th international workshop on technical and scientific aspects of MST radars, 2003