Measuring the earth's synchrotron emission from radiation belts with a lunar near side radio array

The 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/cm³, 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.