STARFIRE: An algorithm for estimating radio frequency interference in orbits around Earth

TL;DR

STARFIRE is a simulation algorithm that estimates terrestrial radio frequency interference in Earth's orbit, aiding the design of space-based experiments for detecting the cosmic 21-cm signal.

Contribution

It introduces a flexible, extendable framework for modeling RFI in Earth's orbit, facilitating experiment planning and RFI mitigation strategies.

Findings

STARFIRE can generate 3D spatio-spectral RFI maps at various altitudes.

It helps identify low-RFI orbits suitable for cosmic signal detection.

The framework is adaptable to different frequencies, antennas, and RFI sources.

Abstract

Ground-based 21-cm experiments targeting the global signal from the periods of Cosmic Dawn (CD) and Epoch of Reionization (EoR) are susceptible to adverse effects presented by i) the ionosphere ii) antenna chromaticity induced by objects in its vicinity iii) terrestrial radio frequency interference (RFI). Terrestrial RFI is particularly challenging as the FM radio band spanning over 88-108 MHz lies entirely within the frequency range of the CD/EoR experiments ($\sim 40-200$ MHz). Multiple space-based experiments have been proposed to operate in the radio-quiet zone on the lunar farside. An intermediate option in cost and complexity is an experiment operating in space in an orbit around Earth, which readily alleviates the first two challenges. However, the effect of RFI in Earth's orbit on the detection of global signal needs to be quantitatively evaluated. We present STARFIRE -- Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth -- an algorithm that provides an expectation of FM seeded RFI at different altitudes over Earth. Using a limited set of publicly available FM transmitter databases, which can be extended by the user community, we demonstrate the use of the STARFIRE framework to generate a three-dimensional spatio-spectral cube of RFI as would be measured in Earth orbit. Applications of STARFIRE include identifying minimum RFI orbits around Earth, producing RFI spectra over a particular location, and generating RFI heatmaps at specific frequencies for a range of altitudes. STARFIRE can be easily adapted for different frequencies, altitudes, antenna properties, RFI databases, and combined with astrophysical sky-models. This can be used to estimate the effect of RFI on the detection of global 21-cm signal from Earth-orbit, and hence for sensitivity estimates and experiment design of an Earth orbiting CD/EoR detection experiment.