2011 SuperDARN Workshop
Electron density estimates of the radar scattering volume for the Radio Receiver Instrument (RRI)-SuperDARN experiment on the ePOP mission
R.G. Gillies, G.C. Hussey, G.J. Sofko, P.V. Ponomarenko, K.A. McWilliams
University of Saskatchewan, Saskatoon, Canada
abstract. The upcoming launch of the Cascade Demonstrator Small-Sat and Ionospheric Polar Explorer (CASSIOPE) satellite, as early as December 2011, has a number of scientific objectives, one of which is to study the micro-physics of the coherent scattering process. The CASSIOPE satellite will contain a suite of eight scientific instruments comprising the enhanced Polar Outflow Probe (ePOP) mission. One instrument, the Radio Receiver Instrument (RRI), will be used in conjunction with the Saskatoon SuperDARN radar for high resolution measurements of the scattering volume. Two specific objectives are to study the coherent radar scatter Doppler velocity measurements and the corresponding electron density in the scattering volume. In the scattering volume it turns out these parameters are related. It has been found that measurements of ionospheric velocities made by HF coherent radars, such as SuperDARN, are underestimated because the refractive index, which is determined by the electron density in the scattering volume, has not been taken into account. Large-scale, background estimates of refractive index from incoherent scatter radar measurements, empirical models such as the International Reference Ionosphere (IRI), or a proxy using elevation angle measurements, have improved comparisons between SuperDARN and other instruments. Nonetheless, the velocities measured by SuperDARN were statistically lower than velocities measured by other instruments. This underestimation is likely a consequence of HF coherent scatter preferentially occurring in regions of the ionosphere with small-scale structures where higher-than-average background electron densities are present. A technique to estimate the electron density in the actual SuperDARN scattering volume (instead of larger-scale background values) has been developed. This technique uses routine shifts in the radar operating frequency to directly measure the electron density at the location of scatter. R esults from this frequency shifting method have indicated that the average electron density in the scattering volume of the SuperDARN radars is appreciably higher than the background densities. Validation and confirmation of this by the RRI-SuperDARN experiment and other instruments on the ePOP satellite will allow for an unprecedented examination of the nature of the scattering structures.