Abstract
Active experiments in the ionosphere use high power radio waves or chemical releases to produce a wide range of plasma disturbances. High-power radio waves or energetic chemical injections can affect the electron density structures, plasma flow, electron and ion temperatures, optical emissions, electrostatic waves and electromagnetic waves emanating from the modified region. Ground based instruments can measure many of the effects of ionospheric modification using radar backscatter, low-light-level imagery, and radio receivers. Space based instruments can, in many instances, record phenomena not detectable solely with the ground sensors. Electrostatic waves and some optical emissions do not propagate to the surface of the earth because of damping and absorption processes. Long-lived effects of ionospheric modification will drift out of the view of ground instruments. For these measurements, satellite based instrumentation is required. The benefits of space-based diagnosis of active experiments are illustrated with examples from (1) tomographic imaging of the F-region disturbances produced by the HF facility at Arecibo and (2) tracking ionospheric bubbles triggered in the equatorial ionosphere by Space Shuttle engine burns. In the next few years, the Communications/Navigation Forecasting Outage System (C/NOFS) and enhanced Polar Outflow Probe (ePOP) on CAScade, Smallsat and IOnospheric Polar Explorer (CASSIOPE) will be available for ionospheric experiments. C/NOFS will provide in situ and radio beacon observations of active experiments near the equator. CASSIPE/ePOP will be used for ELF/VLF measurements as well as in situ observations in conjunction with the radio transmissions from the HAARP facility in Alaska.