Iterative inversion of global magnetospheric ion distributions using energetic neutral atom (ENA) images recorded by the NUADU/TC2 instrument

摘要

A method has been developed for extracting magnetosphericion distributions from Energetic Neutral Atom (ENA) measurements made by theNUADU instrument on the TC-2 spacecraft. Based on a constrained linearinversion, this iterative technique is suitable for use in the case of anENA image measurement, featuring a sharply peaked spatial distribution. Themethod allows for magnetospheric ion distributions to be extracted from alow-count ENA image recorded over a short integration time (5 min). Thetechnique is demonstrated through its application to a set of representativeENA images recorded in energy Channel~2 (hydrogen: 50–81 keV, oxygen:138–185 keV) of the NUADU instrument during a geomagnetic storm. It isdemonstrated that this inversion method provides a useful tool forextracting ion distribution information from ENA data that are characterizedby high temporal and spatial resolution. The recovered ENA images obtainedfrom inverted ion fluxes match most effectively the measurements made at maximumENA intensity.