Auroral arc detection using a COTS spectral photometer for the Auroral Emission Radio Explorer (AERO) CubeSat Mission

Abstract

Auroral phenomena are dynamic in nature: observed events have rich structures that are both spatially and temporally complex, with scientifically interesting features. While optical auroral observations using CCDs or all-sky cameras are common, the aurora also have interesting emission properties at radio frequencies (RF), specifically in low-frequency and high-frequency bands. The Auroral Emission Radio Observer (AERO) is a 6U CubeSat, equipped with a novel electromagnetic Vector Sensor (VS) antenna. The VS will target auroral emission in a measurement band from 100 kHz - 15 MHz, which enables the study of interesting emission types such as Auroral Kilometric Radiation (20 kHz -750 kHz), Medium Frequency Bursts (1.6 MHz - 4.4 MHz) and cyclotron emission (2.8 MHz - 3.0 MHz).

The VS antenna measures 4-meters tip-to-tip once deployed from the CubeSat frame, and expands to form electric dipoles and magnetic loop antennas that are sensitive enough to probe this diverse set of science targets. Having a spacebased platform, such as AERO's vector sensor antenna, positions the detector above the ionospheric plasma frequency which would otherwise limit observations of radio emissions. Novel measurements from AERO's VS antenna require a set of contextual data to validate the fidelity of resulting data products. AERO includes a secondary payload referred to as an Auxiliary Sensor Package (ASP) that will augment VS measurements with contextual optical and magnetic data. The objective of AERO's contextual optical measurement is to detect the presence of auroral emission in multiple spectral bands, namely green-line emission at 557 nm and red-line emission at 630 nm. An AMS AG AS7262 6-channel visual band spectral photometer is selected as the optical sensor.

We present a radiometric model that evaluates the AS7262 sensor's ability to measure target auroral events. We consider a number of different test scenarios, including varying parameters such as auroral source radiance in units of Rayleigh, spacecraft altitude, and others, to fully assess the sensor's ability to detect optical auroral signatures. The mission requirements include a minimum detection of 5 kR for the sensor to satisfy the optical measurement requirement. In our initial assessment, we find that the selected sensor in its current configuration may not be able to meet this requirement. In its current configuration, the sensor may be capable of detecting the presence of auroral events at high levels of intensity, in the over 100 kR range. The model developed in this work indicates that further analysis and possible modification to the front end optic or the sensor itself are needed.

Though the radiometric model presented is tailored for the AS7262 sensor, it is easily adaptable to assess the performance of other auroral imagers. The contextual measurements provided by the ASP will contribute to the success of the AERO CubeSat mission in demonstrating that remote sensing techniques on CubeSat platforms can address unanswered questions about the aurora.