DOI: 10.7302/sc7r-0111
title: Data and Code Set for "Measuring the Earth's Synchrotron Emission from Radiation Belts with a Lunar Near Side Radio Array"

description: This is the README for the LunarSynchrotronArray package, maintained by Dr. Alex Hegedus alexhege@umich.edu 

This code repository corresponds to the Hegedus et al. 2020 (accepted) Radio Science paper, "Measuring the Earth's Synchrotron Emission from Radiation Belts with a Lunar Near Side Radio Array". The arxiv link for the paper is https://arxiv.org/abs/1912.04482.  The DOI link is https://doi.org/10.1029/2019RS006891

;The Earth's Ionosphere is home to a large population of energetic electrons that live in the balance of many factors including input from the Solar wind, and the influence of the Earth's magnetic field. These energetic electrons emit radio waves as they traverse Earth's magnetosphere, leading to short‐lived, strong radio emissions from local regions, as well as persistent weaker emissions that act as a global signature of the population breakdown of all the energetic electrons. Characterizing this weaker emission (Synchrotron Emission) would lead to a greater understanding of the energetic electron populations on a day to day level. A radio array on the near side of the Moon would always be facing the Earth, and would well suited for measuring its low frequency radio emissions. In this work we simulate such a radio array on the lunar near side, to image this weaker synchrotron emission. The specific geometry and location of the test array were made using the most recent lunar maps made by the Lunar Reconnaissance Orbiter. This array would give us unprecedented day to day knowledge of the electron environment around our planet, providing reports of Earth's strong and weak radio emissions, giving both local and global information.

;This set of codes should guide you through making the figures in the paper, as well as hopefully being accessible enough for changing the code for your own array. I would encourage you to please reach out to collaborate if that is the case! Requirements:  
;
CASA 4.7.1 (or greater?) built on python 2.7
Example link for Red Hat 7
https://casa.nrao.edu/download/distro/casa/release/el7/casa-release-4.7.1-el7.tar.gz
Users may follow this guide to download and install the correct version of CASA for their system
https://casa.nrao.edu/casadocs/casa-5.5.0/introduction/obtaining-and-installing
CASA executables should be fairly straightforward to extract from the untarred files.  

gcc 4.8.5 or above (or below?)
GCC installation instructions can be found here: https://gcc.gnu.org/install/

SPICE (I use cspice here)
https://naif.jpl.nasa.gov/naif/toolkit_C.html
As seen in lunar_furnsh.txt which loads the SPICE kernels, you also must download
KERNELS_TO_LOAD = ( '/home/alexhege/SPICE/LunarEph/moon_pa_de421_1900-2050.bpc'
                   '/home/alexhege/SPICE/LunarEph/moon_080317.tf'
                   '/home/alexhege/SPICE/LunarEph/moon_assoc_me.tf'
                   '/home/alexhege/SPICE/LunarEph/pck00010.tpc'
                   '/home/alexhege/SPICE/LunarEph/naif0008.tls'
                   '/home/alexhege/SPICE/LunarEph/de430.bsp' )

All of which can be found at
https://naif.jpl.nasa.gov/pub/naif/generic_kernels/
SLDEM2015_128_60S_60N_000_360_FLOAT.IMG for the lunar surface data by LRO LOLA found at
http://imbrium.mit.edu/DATA/SLDEM2015/GLOBAL/FLOAT_IMG/

description: The Salammbo 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 which provides the brightness distribution of the emission up to 1 MHz from a given observation point.  These brightness maps are included in the distribution for a Lunar vantage point.  

Using Digital Elevation Models from Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) 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 CASA code to image and process the data from our defined array, using SPICE to align the lunar coordinates with the Earth.

The scripts in this repository do the analysis and array simulation to output the noiseless and noisy dirty images that the Lunar array recovers of the Synchrotron emission.