The Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph (LITES)

Abstract:

LITES (Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph) is a compact imaging spectrograph for remote sensing of the upper atmosphere and ionosphere. The instrument has been designed and built, and is undergoing testing and integration to prepare for flight aboard the International Space Station (ISS) as part of the Space Test Program STP-H5 mission. With a passband in the extreme-ultraviolet from 60 to 140 nm, LITES will be able to image several key spectral lines as it observes Earth’s limb, such as the 61.7 and 83.4 nm O⁺ lines to probe the daytime ionosphere, and the 91.1 nm continuum and 135.6 nm neutral oxygen lines to remotely sense the nighttime ionosphere. LITES is one part of a comprehensive ionospheric instrument suite along with the GPS Radio Occultation and Ultraviolet Photometry-Colocated (GROUP-C) experiment which comprises a nadir-viewing UV photometer and a GPS receiver to measure radio occultation. Combined these experiments will provide unprecedented tomographic views of nighttime ionospheric structures on a global scale. We show how LITES observations will be complemented by ground-based data from an international network of digisondes, visible spectrographs, and imagers. These observatories will provide ground-truth for the LITES measurements which will span the globe and fill in the 70% of the Earth where no ground-based measurements are possible. We also present modeled LITES data highlighting improvements in sensitivity, bandwidth, and cadence from earlier-generation observatories. These improvements will allow for advanced studies of longitudinal variability in the low-latitude ionosphere and its transient structures such as ionospheric bubbles.

This work was supported by NSF 1145166 and ONR N00014-13-1-0266 grants. Support for A. Stephan has been provided by the Office of Naval Research. LITES is part of the STP-H5 Payload, integrated and flown under the direction of the DoD Space Test Program.