Reverse Trajectory Approach to Computing Ionospheric Currents to the Special Sensor Ultraviolet Limb Imager on DMSP

The special sensor ultraviolet limb imager was developed by the U.S. Naval Research Laboratory and is deployed on the Defense Meteorological Satellite Program (DMSP) F16 polar-orbiting spacecraft. The instrument is experiencing a level of noise that is, at times, interfering with its proper operation. The noise is correlated with the spacecraft chassis potential. The potentials about DMSP and the resulting ionospheric current entering the instrument were computed to determine if the noise could be due to this current. In order to obtain results of sufficient accuracy, it is necessary to use a reverse trajectory technique that effectively integrates over the thermal distribution of incident ions. The reverse trajectory technique is described in detail. Once the resistance between the mirror surface and the chassis is taken into account, the current computed using this approach shows the same dependence on the chassis potential as the observed noise, which supports the conjecture that ionospheric ions are responsible for the noise