Auroral Tomography for Magnetospheric Precipitation Estimates

Auroral tomography modeling paper

Outdoor all-weather Arctic optical/radio station developed by Michael Hirsch as part of his PhD EE
Outdoor all-weather Arctic optical/radio station developed by Michael Hirsch as part of his PhD EE

By using highly sensitive Andor iXon EMCCD cameras closely separated and aimed at the local magnetic zenith and custom processing, we estimate the electron precipitation characteristics causing the aurora. The cameras have a 9 degree field of view (FOV) and run at their respective maximum sustained frame rate ~50 frames/sec (fps). We thereby study the finest ground-observable auroral spatio-temporal scales and use the high-speed video to obtain the fastest possible (finest time scale) estimates of auroral precipitation.

3x3 figure showing auroral raw images and estimated science quantity
Estimating auroral precipitation drivers using tightly-synchronized, 3 km separated cameras

First principles auroral physics model

To keep the kinetic physics quantitative, we have to consider wavelength-dependent extinction (attenuation) of the atmosphere. The whole-atmosphere expected UV extinction is there, along with big biteouts in IR and near IR. Zenith angle = 90 - horizon elevation angle.

LOWTRAN graph showing atmospheric extinction
Wavelength-dependent extinction predicted by LOWTRAN relevant to ground-based auroral observations at polar latitudes

Time synchronization of high-speed auroral cameras

More than just taking a series of pretty pictures, time transfer (synchronization) is a critical component of this work.

circuit board with wires GPS serial interface
GPSDO with PC interface

We use Jackson Labs Fury GPS Disciplines Oscillators (GPSDO) with a program I developed using National Instruments X-series ASICs for a tightly synchronized triggering and monitoring system. Even $40K cameras don’t always act the way they should.

green oscilloscope screen with traces
Measuring 40 meter cable time delay with a GPSDO--220 nanoseconds

Supporting auroral observation instruments

include the all-sky camera, spectrometer, and multi-megawatt 440 MHz incoherent scatter radar (ISR). The motivating YouTube video is here.