We present a comparison between the backscattering cross sections at 224 and 933 MHz measured with European Incoherent Scatter (EISCAT) radars during the passage of a discrete arc. It shows a difference of 2 orders of magnitude which cannot simply be explained by normal thermal ionospheric density fluctuations. We claim that the observed difference in the scattering cross sections is due to so-called anomalous echoes which typically occur in the vicinity of high-altitude ionospheric perturbations, caused by low-energy particle precipitation. Two possible explanations for the observed differences are discussed: spatial localization and k dependence. Using UHF tristatic observations, we show that there, indeed, is a possibility that the observed echoes are very localized in space. Analyzing the possible k dependence, we show that the experimental geometry used at least in principle will allow us to rule out one of the earlier proposed production mechanisms. ¿ American Geophysical Union 1996