A new automatic method for estimating the peak auroral emission height from all-sky camera images

Abstract

Abstract. This paper presents a new fully automatic method for quickly finding the average peak emission height of a single auroral structure from a pair of all-sky camera images with overlapping fields of view. The peak emission height of the aurora must be estimated in order to calculate several other important parameters, such as horizontal spatial scales, optical flow velocities, and ionospheric electric fields. In most cases the height is not measured, but a value is assumed, often about 110 km. It is unclear how accurate this assumption is. A future statistical study of the auroral height in which the method presented here will be applied to many years of observations will lead to more accurate assumptions of the height with quantitative error estimates, and therefore more accurate estimates of parameters derived using these assumed auroral heights. In the present work the performance of the new method is compared to another recent automatic method. It is found that the new method measures the peak emission height regardless of the shape of the volume emission rate profile, unlike the other recent method. However, the new method is less suitable than the other method for analysis of very wide auroral arcs (> 30 km) or for aurora in the magnetic zenith of one of the images.

Patch Size Evolution During Pulsating Aurora

“…Estimating the patch sizes in physical area requires an assumption for the height of auroral emission. Here, we used the height values calculated for these events in the previous study by Partamies et al (2017) using the method of Whiter et al (2013). The result is a size in square kilometers for each detected patch.…”

Substorm evolution of auroral structures

“…The calculation of arciness is performed for pruned and paired data which only include images containing aurora and exclude data contaminated by other light sources, such as clouds and twilight. By paired data we mean simultaneous images from two neighboring stations with overlapping fields of view giving a good correlation (Pearson correlation coefficient larger than 0.7 [Whiter et al, 2013]). The required correlation guarantees that the same auroral structure is seen from two stations.…”

High-speed stereoscopy of aurora

“…It has been known for a long time that aurora manifests itself in many rapid variations (Stormer, 1955). The rapidly varying aurora has recently been studied as important phenomena to visualize the wave-particle interactions working in the magnetosphere-ionosphere coupled regions (Dahlgren et al, 2008;Kataoka et al, 2011aKataoka et al, , b, 2012Yaegashi et al, 2011;Whiter et al, 2010) and in the magnetosphere (Miyoshi et al, 2010(Miyoshi et al, , 2015aNishiyama et al, 2014;Kataoka et al, 2015). The time-varying emission altitude of such various types of rapidly varying aurora contributes especially to understand not only the generation mechanisms but also their possible impact on the atmosphere (Miyoshi et al, 2015b) because the emission altitude contains information of the energy of precipitating electrons and indicates the stopping height of electrons.…”

“…Stereoscopy of aurora has also been conducted to determine the emission altitude since the beginning of auroral research (Stormer, 1955), and many sophisticated stereoscopic analyses have been carried out worldwide (e.g., Stenbaek-Nielsen and Hallinan, 1979;Frey et al, 1996;Ivchenko et al, 2005;Whiter et al, 2013). Most recently, Kataoka et al (2013) performed all-sky stereoscopy of aurora using twin fish-eye DSLR cameras located 8 km apart, which may give an interesting pathway to open citizen science.…”