Proceedings with Extended Abstracts (single PDF file) - Radio ...

30 secFig. 10 Temporal variation of SDI-FDI-determined parameters: dr = (∆x 2 +∆y 2 + ∆z 2 ) 1/2 = radial distance in the radar range gate volume (at 6.3 ± 0.15 km),am = signal amplitude, ze = zenith incidence angle, az = azimuth incidence angle,vr = radial velocity. These measurements were done with the MU radar inOctober 1998 (Röttger et al., 2000). The lower right-hand-side inset shows themodel of scattering/reflecting regions as discussed by Röttger (1998).The combination of the SDI with the FDI technique allows three-dimensional tracing of locationsof normal MST radar echoes from the clear and cloudy air as well. Here we have to regard,though, the fact that we do not have a localized (hard) target as in the case of lightningechoes, but a volume (soft) target. This was considered by Röttger (1998), who pointed outthat one can only measure the phase center location and its spatial and temporal variation. Thephase center is the mean location of the vector sum of signals from a certain number of individual,maybe even overlapping, targets in the radar volume. Unless one has a very-high-resolution,large-baseline spaced antenna system (or an extremely narrow antenna beam), whichallows high spatial resolution in the SDI mode, and a very wide frequency range in the FDImode (or a very short pulse allowing range resolutions of some ten meters), one cannot separatethe individual targets. A usual SDI spaced-antenna set-up of 3-4 receiving arrays and alimited number of FDI frequencies then allows to determine only the mean phase center as socalledeffective target location.Fig. 10 shows the temporal variations of the parameters, which can be measured with thistechnique. The display is in arbitrary units, since we consider only the mutual variations ofthese parameters. The amplitude variations have the characteristics of beating (superposition)of two signals, i.e. here we observed just two dominating target echo regions. This is a verycommon observation. Several amplitude minima occur when the zenith angle is large, theazimuth angle changes or even jumps, and the radial distance changes as well. This isregarded as additional prove that signals from two dominating regions were beating eachother.To understand more about the scattering-reflection mechanism we regard this techniqueessential, looking into the micro-scale variations of the refractivity structures overhead.454