Measuring the Earth's Synchrotron Emission From Radiation Belts With a Lunar Near Side Radio Array

Abstract

AbstractThe high kinetic energy electrons that populate the Earth's radiation belts emit synchrotron emissions because of their interaction with the planetary magnetic field. A lunar near side array would be uniquely positioned to image this emission and provide a near real time measure of how the Earth's radiation belts are responding to the current solar input. The Salammbô code is a physical model of the dynamics of the three‐dimensional phase‐space electron densities in the radiation belts, allowing the prediction of 1‐keV to 100‐MeV electron distributions trapped in the belts. This information is put into a synchrotron emission simulator that provides the brightness distribution of the emission up to 1 MHz from a given observation point. Using Digital Elevation Models from Lunar Reconnaissance Orbiter Lunar Orbiter Laser Altimeter data, we select a set of locations near the Lunar sub‐Earth point with minimum elevation variation over various‐sized patches where we simulate radio receivers to create a synthetic aperture. We consider all realistic noise sources in the low‐frequency regime. We then use a custom Common Astronomy Software Applications code to image and process the data from our defined array, using SPICE to align the lunar coordinates with the Earth. We find that for a moderate lunar surface electron density of 250/cm , the radiation belts may be detected every 12–24 hr with a 16,384‐element array over a 100‐km‐diameter circle. Changing electron density can make measurements 10 times faster at lunar night and 10 times slower at lunar noon.