Imitial Observations and Analysis of Whistler Mode Echoes Received by RPI on IMAGE V. S. Sonwalkar, X. Chen, J. Harikumar Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK 99775 D. L. Carpenter, M. Salvati, T. F. Bell STAR Laboratory, Stanford University, Stanford, CA 94305 W. W. L. Taylor Raytheon ITSS, Goddard Space Flight Center, Greenbelt, MD, USA S. F. Fung and J. L. Green NASA Goddard Space Flight Center, Greenbelt, MD, USA B. W. Reinisch University of Massachusetts, Center for Atmospheric Research, Lowell, MA, USA J. Goldstein and P. Reiff Rice University, Houston, TX, USA We report on initial observations and analysis of whistler mode echoes received by RPI on IMAGE. Whistler mode echoes have been identified on a number of days during the period when IMAGE was at low altitude (£ 2000-6000 km) near its perigee in the southern hemisphere. The observed whistler echoes have frequencies below local electron cyclotron frequency. The echoes are in the frequency range ~13-300 kHz and show time delays of a fraction of a second, and longer time delays at lower frequencies, typical of whistler mode propagation. Ray tracing simulations done in a limited number of cases indicate that these echoes are the result of reflections of RPI signals from the Earth-ionosphere boundary. By comparing measured time delays of RPI signals with those from ray tracing simulations it is possible to determine the electron density along the ray paths. In one case, 5 May 2000, when IMAGE was at an altitude of ~ 4000 km and invariant latitude of ~ 70¼, the ray tracing analysis leads to an electron density of ~ 800 el/cc at the satellite altitude (~4000 km) with a R-4.5 dependence. These results indicate that whistler mode propagation analysis performed on echoes obtained on IMAGE at high latitude can be used to obtain improved electron density models in the high latitude magnetosphere. _______________ Presented at the Fall American Geophysical Union Meeting, San Francisco, CA., December 15-19, 2000