Time Delay Integration Imaging of the Nighttime Ionosphere from the ICON Observatory

Abstract One of the objectives Far UltraViolet (FUV) imager on Ionospheric Connection Explorer (ICON) spacecraft is to make high resolution images nighttime near equatorial oxygen 135.6 nm airglow emission. This emission largely product O + ion re-combination and therefore intensity a proxy for remote measurement ionospheric density. The ICON FUV instrument capable imaging night glow by viewing Earth’s limb from above left side taking rapid exposures co-adding resultant 12 seconds. To improve compress resulting data new type Time Delay Integration (TDI) technique was developed, which involves transforming into distorted frame so that displacement due orbital motion becomes singular constant vector all pixels. Operating in this transformed it possible co-add shift retain minimize required bandwidth. transformation needs modeling object distance Two models, “limb” “sub-limb” are used upper lower parts images, respectively. At input there rotatable mirror, allows directing optic axis plane local magnetic field. co-added sec down linked re-assembled ground maps showing an entire pass. first report performance newly developed TDI system. with its low inclination (27 degree) orbit provides extensive longitudinal coverage each complementing GOLD or TIMED. During 179 orbits October 2021 saw significant densities 76% orbits. latitudes ionization clearly associated anomaly (EIA). showed structuring during 34% when position view EIA. In coordinated observations observed regular form Equatorial Plasma Bubbles (EPB-s). Comparing 2018, significantly fewer EPB-s month 2021. integrated sub-limb tested using star should have seen structures less than 10 km. From taken shortest repetition EPB-were 350 km peak peaks.