Kanzelhöhe Observatory: Instruments, Data Processing and Data Products

Abstract

Kanzelhöhe Observatory for Solar and Environmental Research (KSO) of the University of Graz (Austria) is in continuous operation since its foundation in 1943. Since the beginning, its main task was the regular observation of the Sun in full disc. In this long time span covering almost seven solar cycles, a substantial amount of data was collected, which is made available online. In this article we describe the separate processing steps from data acquisition to high level products for different observing wavelengths. First of all we present in detail the quality classification, which is important for further processing of the raw images. We show how we construct centre-to-limb variation (CLV) profiles and how we remove large scale intensity variations produced by the telescope optics in order to get images with uniform intensity and contrast. Another important point is an overview of the different data products from raw images to high contrast images with heliographic grids overlaid. As the data products are accessible via different sources, we also present how to get information about the availability and how to obtain these data. Finally, in an appendix, we describe in detail the information in the FITS headers, the file naming and the data hierarchy.

Full-disc Ca ii K observations—A window to past solar magnetism

“…The most important step is to identify the solar disc on the images. This is usually done in an automatic way with edge detection techniques, such as Sobel filter, a Canny edge detector, or Hough transform (Veronig et al, 2000;Zharkova et al, 2003;Curto et al, 2008;Ermolli et al, 2009a;Chatterjee et al, 2016;Suo, 2020;Zhu et al, 2020;Pötzi et al, 2021), while in some cases this was done manually by clicking with the computer mouse at three to five points at the limb (e.g. Priyal et al, 2014).…”

“…The first group of methods determine a radially symmetric limb darkening background (Brandt and Steinegger, 1998;Johannesson et al, 1998;Walton et al, 1998;Denker et al, 1999;Zharkova et al, 2003;Diercke and Denker, 2019;Pötzi et al, 2021). This is done by fitting polynomial functions (typically fourth order) along the average radial profile of the solar disc in terms of μ (cosine of the heliocentric angle).…”

“…The North-South asymmetry of solar cycles has usually been studied with sunspot data (e.g. Ravindra et al, 2021;Veronig et al, 2021), but Dorotovič et al (2007) 2020) is, however, simply mirroring that from sunspot data, as these authors used the composite of full-disc plage areas by Chatzistergos et al (2019b), which they separated into the north and south components by imposing the same asymmetry level as found in Royal Greenwich observatory sunspot area data. Using Kodaikanal plage areas from Chatterjee et al (2016) over cycles 14-21 derived for each hemisphere separately Chowdhury et al (2022) found only three cycles (14, 15, and 21), for which the activity peak roughly coincided in both hemispheres, while higher activity was found in the northern hemisphere for all cycles except 14, 17, and 21.…”

Variation in solar differential rotation and activity in the period 1964–2016 determined by the Kanzelhöhe data set

“…We used two procedures to determine the heliographic positions of sunspot groups: an interactive procedure (KSO sunspot drawings, 1964(KSO sunspot drawings, -2008, and an automatic procedure (KSO white-light images, 2009(KSO white-light images, -2016. The KSO observations, data products, and sunspot drawing were described by Pötzi et al (2016Pötzi et al ( , 2021. For the interactive procedure, a software package called Sungrabber 1 (Hržina et al 2007) was used.…”

Sun CubE OnE: A multi-wavelength synoptic solar micro satellite

“…• ground based networks and synoptic observatories such as GONG (Harvey et al, 2011), Kanzelhöhe Observatory (Pötzi et al, 2021), MOTH (Jefferies et al, 2006) and TSST (Giovannelli et al, 2020).…”