Near-Approach Imaging Simulation of Low-Altitude ENA Emissions by a LEO Satellite

Abstract

We simulate a 2-D ENA coded modulation imager on board a polar orbit satellite. An imaging measurement, which can realize continuous monitoring of low-altitude ENA emission sources, is applied to the evolution process of energetic ion events. The present simulation results show that: (1) Low earth polar orbit satellites can approach ENA emission sources from inside and outside the inner radiation belt. At low altitude, ENA images can be collected with a time resolution of only 5 s, enabling for the first time observation of the evolution process of energetic ion events, on top of determining a global distribution pattern of energetic ions; (2) For tracing energetic particle trigger source of substorm, the propagation distance of energetic particles can be calculated by using time difference of ENA energy spectrum response of different energy channels; (3) Due to the proximity of the ENA emission source, the ENA imager will respond to medium and small-magnitude signals of substorms, which will help sample continuous collection and statistical analysis of massive data under various geomagnetic activities, and provide important data support for space weather forecasts.

Simulation of ENA Imaging Measurements on a Geosynchronous Orbit

“…In previous inversion models, we always assumed that the ring current energetic ions producing ENA emission bounced back and forth between the north and south poles along the closed magnetic field line, and its corresponding ENA emission source should be symmetrical between north and south. Therefore, the contingency of the latitude variation of ion fluxes is excluded from the inversion calculation and replaced by a theoretical model [11,12] . •sr -1…”

“…Here ΔE is the energy range within; ΔT is the integral time for the pixel; ΔΩ is the solid angle of the volume element pointing to the δ, ε pixel; j ion is Ion differential flux at the Integral volume element; A(δ, ε) is the response function of a detector [13] ; σ (E) is the charge exchange cross sections [16] ; n(r, φ, θ) is the exospheric neutral atomic density, where r is geocentric distance, φ is longitude, and θ is latitude; dV is the volume element integral along the line of sight of the detector. The ion flux in the ring current region may be expressed in the form of [12]…”

“…Previous magnetospheric ENA imaging exploration satellites mostly adopt large elliptical orbits with large inclination [4][5][6] , with apogee over tens of thousands km, and ENA emission signals from the north and south polar regions cannot be observed at the same time. The simulation and inversion models are all based on the assumption of the north-south conjugate change of the reciprocating bounce of energetic ions along magnetic lines [7][8][9][10][11][12][13] . The ENA imaging measurement and inversion only focus on the radial and azimuth changes of the Energetic ion distribution in the ring current region.…”

Simulation of Dynamic Evolution of Ring Current Ion Flux by a Lunar Base Energetic Neutral Atom (ENA) Imaging

“…where ΔE is the energy range within, ΔT the integral time for the pixel, and ΔΩ the solid angle of the volume element pointing to the δ, ε pixel; jion represents ion differential flux at the integral volume element, A(δ, ε) the response function of a detector [12], and σ(E) the charge exchange cross sections [13]; n(r, φ, θ) is the exospheric neutral atomic density, where r represents the geocentric distance, φ the longitude, and θ the latitude; and dV is the volume element integral along the line of sight of the detector. The ion flux in the ring current region may be expressed in the form of [14] 1 Table 1.…”