<title>Experiment for studying spatial and temporal behavior of the ionosphere</title>

Abstract

We present the concept for an instrument designed to map and monitor the ionosphere from geostationary orbit. This instrument will be used to study the spatial and temporal behavior of mesoscale (> 10 km) ionospheric structures. The instrument is designed to primarily operate at night as irregularities are generally more prevalent during the evening. The instrument will be sensitive enough to gather a high signal-to-noise image viewing the nadir in approximately 100 seconds. The instrument can also be operated as a limb imager. The instrument will image a 1.6° degree field-of-view with 10 km spatial resolution. The experiment will use a two-axis gimbal to point to various points on the limb and disk of the Earth. The instrument consists of an extreme ultraviolet (EUV) imager and a far-ultraviolet (FUV) imager. The EUV imager will operate at 83.4 nm using a low resolution imaging spectrograph to set the passband. The O II 83.4 nm emission is produced by photoionization of O during the daytime. Above the limb, this emission can be used to determine altitude distribution of the O + density. The FUV imager will operate at 130.4 , 135.6, and 143.0 nm. At night, The O I 130.4 and O I 135.6 nm emissions are produced by primarily by radiative recombination, and therefore these emissions provide useful ionospheric diagnostics at night. During the daytime, the 130.4 and 135.6 nm lines are primarily produced by photoelectron impact excitation of O; however the 130.4 nm line is also excited by resonant scattering of sunlight. The O I 130.4 and 135.6 nm lines provide information on the O density during the daytime. The instrument will map the daytime N 2 column density using the Lyman-Birge-Hopfield bands near 143.0 nm.