The transmit antennas are tuned under computer control to the sounding frequencies. Cosmic noise and receiver noise plays a minor role. RPI applies pulse compression techniques and spectral coherent integration to enhance the signal to noise ratios. The level of the noise floor will vary with time and spacecraft location and we expect to see echoes from more than 10 RE during favorable conditions and 5 RE or less during disturbed conditions. The range resolution was chosen as 240 km, setting the pulse width to 3.2 ms and the receiver bandwidth to 300 Hz.
Radio imaging is required to identify the locations of the reflecting plasma structures.
For a voltage SNR of 100 the accuracy is 1o. The polarization ellipse and its orientation relative to the orientation of the transmitted wave can also be calculated from the measurements making it possible to determine the reflection coefficients and the Faraday rotation. Profile inversion algorithms have been tested on simulated data and have been found to accurately reproduce the input electron density profile. Within the plasmasphere and at low altitude over the southern polar region, RPI may at times operate in the whistler mode, transmitting at frequencies below the local electron gyrofrequency to study wave-particle interactions, plasmasphere fine structure, and ionosphere signal penetration.