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UEC Int’l Mini-Conference No.52 53

Study of auroral fine structure using high spatio-temporal resolution

optical observations

Wandal WINN , Keisuke HOSOKAWA
∗
Department of Computer and Network Engineering
The University of Electro-Communications
Tokyo, Japan

Keywords: Aurora, Pulsating Aurora, Astrometric Calibration, qCMOS Camera.

Abstract
The aurora is a well-known phenomena which occurs in the polar regions of the Earth, at around
an altitude of 100 km. It is caused by energetic electrons from the magnetosphere precipitating into
the ionosphere along the geomagnetic field lines. These electrons collide with atoms and molecules in
the Earth’s atmosphere, and the energy is released in the form of light. Auroras are classified into
two broad categories: the discrete aurora, which has a distinct arc-like shape, and the diffuse aurora,
which has an indistinct patchy shape. Most of the diffuse auroras are known to show a quasi-periodic
luminosity modulation called pulsating aurora. Recent observations with high temporal resolution have
been advancing our understanding of the physical mechanisms causing pulsating auroras. However,
the origin or formation process of their complex spatial structures remain unclear, which is mainly due
to the insufficient spatial resolution of conventional fisheye lens-based all-sky camera systems used for
auroral imaging. To solve this problem, we have recently set up a high resolution optical system in
Skibotn, Norway to resolve the fine-scale spatial structure of pulsating auroras in greater detail. This
system is comprised of a Hamamatsu Photonics C15550-20UP (ORCA-Quest qCMOS camera) with
a narrow field-of-view F1.4 lens (Kowa LM8HC). The C15550-20UP camera has spatial resolution of
4096×2304 pixels, which will allow us to resolve sub-kilometer scale structures of auroras near the
zenith. We put a wide-band optical filter (BG3 glass filter) on top of the lens to remove contributions
of slower aurora emissions, such as the ones at 557.7 nm and 630.0 nm, and capture sub-second fast
modulations of aurora. Since the installation in October 2023, the camera has been routinely operated
at a rate of 20 frames-per-second (FPS), which is accurately synchronized by GNSS. We have also
began initial analyses of the images transferred from Norway. An important part of the initial data
analysis is the calibration of the field-of-view for accurately mapping the images from the camera onto
the geographic coordinate system. This can be achieved through Astrometric Calibration, where we
use the constellations visible in the background of the image to determine its field of view in the sky.
Combining this info with the time of the image and the camera’s geographical coordinates, we can
derive the elevation and azimuthal angles of all the pixels in the image and eventually determine the
latitude and longitude of each pixel in the image at the altitude of auroral emission (100 km). This
will enable us to project the obtained auroral images onto the surface of the Earth at 100 km altitude
as viewed from space. In the presentation, we will introduce the above-mentioned procedures of the
field-of-view calibration, along with some initial findings in the aurora images from the arctic.

The author is supported by (SESS) MEXT Scholarship.
*