Tomographic Reconstruction of Plasma Density for the GNEISS Rocket Mission

The GNEISS mission (Lynch 397 and 398), which launched in February of 2026, was a near-simultaneous launch of two sounding rockets, intended to study the current closure and along-arc structure of a non-sheetlike discrete auroral arc. It aimed to gather as complete a picture as possible of the auroral arc system by making use of a variety of heterogeneous data sources, including remote sensing from multiple cameras and the PFISR Radar, and several in-situ particle and field instruments carried by each rocket. Each rocket also carried an RF transmitter as part of the Lattice Beacon system, which broadcast a nearly continuous-wave (CW) signal to 10 ground-based sites across interior Alaska. By comparing the polarization angle measured by each ground site to the known spin phase of the rocket, TEC can be simultaneously estimated for 20 lines of sight throughout the flight, and using tomographic reconstruction techniques can be used to form a 2d or even 3d estimate of plasma densities under the flight trajectory. This information will be compared or synthesized with the various other density measurements to form as complete a picture as possible of the ionospheric density distribution during the GNEISS launch. When combined with current and flow data, this density distribution will help us better understand the 3d structure and time evolution of current closure in non-sheetlike auroral arcs.