A Comparison of Electron Densities Derived by Tomographic Inversion of the 135.6 nm Ionospheric Nightglow Emission to Incoherent Scatter Radar Measurements

The 135.6-nm emission of atomic oxygen has become a workhorse for satellite remote sensing of the nighttime ionosphere. Previous work on interpreting the 135.6-nm emission established the importance of properly modeling the mutual neutralization and radiative recombination contributions to the volume emission rate and emphasized the importance of modeling and interpreting the transfer and transport of the radiation. Recently, we developed and published a new inversion approach called Volume Emission Rate Tomography, which handles the radiation transfer as part of the tomography process. We compare electron density distributions derived using the Volume Emission Rate Tomography technique to interpret the 135.6-nm measurements made by the Special Sensor Ultraviolet Limb Imager instruments aboard the Defense Meteorological Satellite Program satellites in 2010. These retrievals are validated against electron densities measured during overflights of the Advanced Research Project Agency Long-range Tracking and Identification Radar incoherent scatter radar. The mean percentage difference between the Special Sensor Ultraviolet Limb Imager-derived electron densities and those measured by Advanced Research Project Agency Long-range Tracking and Identification Radar was 14%, when radiative recombination was the only source considered in the inversion process. When the mutual neutralization and radiation transport sources of emission are included in the inversions, the mean percentage decreased to 4%, thereby confirming that these sources are necessary to accurately derive the electron density from the 135.6-nm emission.