Use of dispersive effects for density profile reconstruction from pulse radar reflectometry measurements alone

Reflectometry deduces the density profiles from the time of flight measurem ents for different frequencies of the probing wave. Pulse radar reflectomet ry allows the time of flight measurements at only a few discrete frequencie s (typically 10 frequencies), which can lead to bad profile reconstruction. In order to improve the profile determination, it is proposed to use a dis persive effect of higher order, namely the pulse broadening. It is shown th at usual methods of profile reconstruction are then improved. Particular at tention is paid to the initialization problem, which is crucial in O-mode r eflectometry. Initialization methods that use only reflectometry measuremen ts have been developed. The sensitivity df each method to the measurement e rrors is discussed. Errors due to density fluctuations have been investigat ed numerically. For density fluctuations with moderate amplitude, the time of flight can be significantly modified whereas the pulse broadening is mos tly unchanged. It is shown that, even with significant errors (10% on the t ime of flight, up to 40% on the pulse broadening) the profile initializatio n can be improved by using both time of flight and optimal length. The dens ity profile is then reconstructed with an acceptable accuracy.