Spacecraft Potential Measurements on Board INTERBALL-2 and Derived Plasma Densities

The electric potential of the spacecraft INTERBALL-2 (Auroral Probe) has been analyzed for a period of 18 months starting in October 1996. Data from the instrument IESP, as received and filtered onboard the spacecraft by the instrument RON, serve as the main database. The data have been organized in MLT and invariant latitude, and the dependence on various geophysical parameters has been studied. Using relations between spacecraft potential and plasma density from the literature, the plasma density between 16000 and 19000 km altitude is derived. The relative variations of the densities not only reflect the typical global structure, but also exhibit features of the plasmasphere and auroral region on smaller scales. The accuracy of the absolute density values obtained by this method is discussed.