Due to a large number of automatic auroral camera systems on the ground, image data analysis requires more efficiency than what human expert visual inspection can provide. Furthermore, there is no ...solid consensus on how many different types or shapes exist in auroral displays. We report the first attempt to classify auroral morphological forms by an unsupervised learning method on an image set that contains both nightside and dayside aurora. We used 6 months of full-colour auroral all-sky images captured at a high-Arctic observatory on Svalbard, Norway, in 2019–2020. The selection of images containing aurora was performed manually. These images were then input into a convolutional neural network called SimCLR for feature extraction. The clustered and fused features resulted in 37 auroral morphological clusters. In the clustering of auroral image data with two different time resolutions, we found that the occurrence of 8 clusters strongly increased when the image cadence was high (24 s), while the occurrence of 14 clusters experienced little or no change with changes in input image cadence. We therefore investigated the temporal evolution of a group of eight “active aurora” clusters. Time periods for which this active aurora persisted for longer than two consecutive images with a maximum cadence of 6 min coincided with ground-magnetic deflections, and their occurrence was found to maximize around magnetic midnight. The active aurora onsets typically included vortical auroral structures and equivalent current patterns typical for substorms. Our findings therefore suggest that our unsupervised image clustering method can be used to detect auroral breakups in ground-based image datasets with a temporal accuracy determined by the image cadence.
The Rocket Experiment for Neutral Upwelling 2 (RENU2) rocket was launched on 13 December 2015 at 07:34 UT. The payload transited the cusp region during a neutral upwelling event, supported by a ...comprehensive set of onboard and ground‐based instrumentation. RENU2 data highlight two important processes. One is that a proper understanding of neutral upwelling by Poleward Moving Auroral Forms (PMAFs) requires a treatment that mimics the quasiperiodic passage of a sequence of PMAFs. As a PMAF reaches a flux tube, its physical consequences must be determined including the residual history of effects from previous passages, implying that understanding such a process requires an accounting of the system hysteresis. Second, RENU2 observations suggest that neutral density enhancements driven by precipitation and/or Joule heating can be highly structured in altitude and latitude. In addition, timescales involving neutral dynamics suggest that the structuring must be slowly changing, for example, over the course of 10 to tens of minutes.
Key Points
RENU2 measured particles and fields within a PMAF‐driven neutral upwelling event
PMAFs consist of multiple thin arcs; poleward motion leads to a quasiperiodic heating process
Neutral upwelling (driven by soft precipitation) is dynamic and highly structured in space
Time History of Events and Macroscale Interactions during Substorms (THEMIS) is a NASA MIDEX mission scheduled for launch in 2006. THEMIS will consist of five magnetospheric satellites in equatorial ...orbits. Three of the spacecraft will have apogees around 12
Re, while the fourth and fifth will have apogees at
∼
20
and
∼
30
Re
. The
12
,
20
, and 30
Re apogee orbits will have periods of one, two, and four sidereal days, respectively, meaning that all five spacecraft will be at or near apogee in the same meridian every four sidereal days. Furthermore, these conjunctions will always occur over central Canada throughout the mission duration. The five THEMIS satellites will be instrumented with particle and field detectors for measuring relevant plasma parameters, fields, and bulk velocities in the central plasma sheet (CPS). The THEMIS constellation will bracket the current disruption (CD) and near-earth neutral line (NENL) regions and will provide for the first time an opportunity for unambiguous identification of the radial position in the CPS where the substorm process initiates. The primary scientific objective for THEMIS is to determine which of these processes is responsible for substorm onset. THEMIS cannot close this question without complementary ground-based observations in North America. To this end, THEMIS requires the deployment of 20 white light all-sky imagers (ASIs) in a continent-wide array. These ASIs will operate with a cadence of at least one image every 5
s, and will provide mission critical onset and early expansive phase information. In this paper, we present observations from the prototype THEMIS ASI for one substorm event. This image data demonstrates that the THEMIS ASI has the temporal and spatial resolution necessary to meet the mission requirements. Further, in this event we find that the growth phase arc shows wavelike azimuthal structuring and a brightening that occurs virtually simultaneously along the entire length of the arc that is within the ASI field of view. We attribute this wavelike structure to structure in the CPS. We anticipate that the THEMIS ASI array and
in situ data will allow for the elucidation of the CPS process that generates this azimuthal structure.
The electromagnetic coupling of the solar wind, Earth's magnetic field, and the upper atmosphere allows us to study the near-Earth space phenomena by monitoring the auroral displays in the polar ...regions. Ground-based networks facilitate spatial and temporal resolutions that are not possible with satellite instruments-they also produce enormous amounts of data to be stored and processed. While automated image analysis methods for auroral research are beginning to emerge, the normal approach is to visually examine images and then manually label and sort the data. We revisit a key question concerning the existence of aurora in an image: Not all images contain auroral light, and the visibility to the upper atmosphere depends on cloud cover. Detection of aurora is a fundamental step to limit further processing to only those images that are of interest. We quantitatively evaluated a selection of numeric image features that have been used in earlier studies and assess a brightness-invariant feature. We achieved error rates around 6%-8% with subsecond execution times. To the best of our knowledge, we are the first to report results in classifying auroral images where the Moon is allowed to be visible.
Automatic Auroral Detection in Color All-Sky Camera Images Rao, Jayasimha; Partamies, Noora; Amariutei, Olga ...
IEEE journal of selected topics in applied earth observations and remote sensing,
12/2014, Volume:
7, Issue:
12
Journal Article
Peer reviewed
Open access
Every winter, the all-sky cameras (ASCs) in the MIRACLE network take images of the night sky at regular intervals of 10-20 s. This amounts to millions of images that not only need to be pruned, but ...there is also a need for efficient auroral activity detection techniques. In this paper, we describe a method for performing automated classification of ASC images into three mutually exclusive classes: aurora, no aurora, and cloudy. This not only reduces the amount of data to be processed, but also facilitates in building statistical models linking the magnetic fluctuations and auroral activity helping us to get a step closer to forecasting auroral activity. We experimented with different feature extraction techniques coupled with Support Vector Machines classification. Color variants of Scale Invariant Feature Transform (SIFT) features, specifically Opponent SIFT features, were found to perform better than other feature extraction techniques. With Opponent SIFT features, we were able to build a classification model with a cross-validation accuracy of 91%, which was further improved using temporal information and elimination of outliers which makes it accurate enough for operational data pruning purposes. Since the problem is essentially similar to scene detection, local point description features perform better than global- and texture-based feature descriptors.
Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground‐based and, nowadays more and more, also by space‐based measurements. ...Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on 3 December 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground‐based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a CubeSat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modeling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground‐based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modeling demonstrate how even a small 1‐Unit (size: 10 × 10 × 10 cm) CubeSat and its camera, build using cheap commercial off‐the‐shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground‐based observations.
Plain Language Summary
Auroras, or polar lights, have been imaged by ground‐based terrestrial cameras for a long time. However, auroras can also be observed from space with cameras mounted on spacecraft. In the last few years, a number of very small satellites, so‐called nanosatellites with masses less than 10 kg, have been developed and launched into so‐called low Earth orbits at altitudes between 300 and 600 km. These small and light satellites are much cheaper than traditional large and heavy satellites, the masses of which could easily exceed hundreds of kilograms. Therefore, it is anticipated that nanosatellites will provide new possibilities to investigate auroras. In this study, we analyze, to our knowledge, the first image of an aurora taken by a nanosatellite. The satellite is a small, 10 × 10 × 10 cm, Suomi 100 satellite which was launched in December 2018. We show how the obtained auroral image can provide new information about auroras when it is combined with ground‐based observations and numerical modeling. When additional cameras will be included in the design and fabrication of small satellites, we will be able to increase our understanding of auroras and, consequently, the effects of the Sun on the Earth and beyond.
Key Points
The concept of imaging aurora toward the Earth's limb by a CubeSat camera is demonstrated
The dark background available in the Earth‐limb viewing direction facilitates imaging of dim auroras, e.g., for auroral tomography purposes
The analysis shows that auroral imaging at low Earth orbit can provide a new context for ground‐based auroral and ionospheric observations
The Rocket Experiment for Neutral Upwelling 2 (RENU2) rocket was launched on 13 December 2015 at 07:34 UT. The payload transited the cusp region during a neutral upwelling event, supported by a ...comprehensive set of onboard and ground‐based instrumentation. RENU2 data highlight two important processes. One is that a proper understanding of neutral upwelling by Poleward Moving Auroral Forms (PMAFs) requires a treatment that mimics the quasiperiodic passage of a sequence of PMAFs. As a PMAF reaches a flux tube, its physical consequences must be determined including the residual history of effects from previous passages, implying that understanding such a process requires an accounting of the system hysteresis. Second, RENU2 observations suggest that neutral density enhancements driven by precipitation and/or Joule heating can be highly structured in altitude and latitude. In addition, timescales involving neutral dynamics suggest that the structuring must be slowly changing, for example, over the course of 10 to tens of minutes.
Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. ...Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on Dec. 3, 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a cubesat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modelling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modelling demonstrate how even a small 1-Unit (size: 10 cm x 10 cm x 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.
Determining the skeletons of the auroras Syrjasuo, M.T.; Pulkkinen, T.I.
Proceedings 10th International Conference on Image Analysis and Processing,
1999
Conference Proceeding
The auroral emissions observed in the high-latitude regions encircling the magnetic poles are a key element in studying plasma physical processes in the near-Earth space, the magnetosphere. The ...Finnish Meteorological Institute operates five digital all-sky cameras, which routinely monitor the auroral emissions in Northern Finland, Sweden, and Svalbard; each camera records an image of the full sky at 20 second intervals. In this paper, we develop a method that allows us to examine such a large data set by classifying the images through determining the shape skeletons of the auroral forms in each auroral image. Shape skeletons are a commonly used representation of object shapes in machine vision applications. Once determined, shape skeletons have the advantage that they can also be used to represent noisy or unevenly distributed data. Here we apply a skeletonising algorithm to determine the skeletons of auroras in a noisy environment. The algorithm is based on a batch mode self-organising map. The results can be further improved by implementing understanding of the auroral physics to the algorithm.
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