1.

Introduction

In the consumer market, CMOS detectors have already replaced CCD sensors in many applications. This transition from CCD to CMOS technologies is also happening in astronomical and solar instrumentation because the noise characteristics of the CMOS devices significantly improved in recent years.^{1 –3} Fast, large-format CMOS detectors reach and exceed full High Definition (HD) resolution ($1920<span\; class="naked\_sign">\times </span><span\; class="naked\_aural">ばつ</span>1080\text{pixels}$) and can achieve image acquisition rates of 50–100 Hz. Such camera systems are ideally suited for current high-resolution solar telescopes, which rely on adaptive optics (AO)⁴ and image restoration⁵ to reach diffraction-limited performance across a field-of-view (FOV) of about 100′′ in diameter. Even though the AO correction decreases with distance from the lock point,^{6 ,7} partial AO correction still aids image restoration across a large FOV. In addition, image restoration methods were developed and delivered near diffraction-limited data even before AO systems were available, and nowadays the methods include a proper treatment for the optical transfer function (OTF) with AO correction.

Spectral imaging of the solar chromosphere in the visible and near-infrared requires narrow-band filters with passbands $\mathrm{\Delta }\lambda <0.1\mathrm{nm}$. Such narrow passbands facilitate isolating the line cores of strong chromospheric absorption lines such as Ca ii H at 396.8 nm, $\mathrm{H}\alpha$ at 656.3 nm, and He i at 1083.0 nm,^{8 –10} among others. In 1933, Lyot¹¹ introduced the first narrow-band filter for solar spectral imaging combining birefringent and polarizing elements. The working principle of the filter was independently discovered by Öhman.¹² Since then, Lyot-Öhman filters were commonly used at solar observatories around the world. The Universal Birefringent Filter (UBF) can be considered as an intermediate step between Lyot-Öhman filters and Fabry-Pérot interferometers.¹³ However, only the latter can achieve a higher photon flux per diffraction-limited pixel. An example is the single-etalon visible imaging magnetograph (VIM)¹⁴ at the 1.6-meter goode solar telescope (GST), nowadays called visible imaging spectrometer (VIS), which is mainly used as an $\mathrm{H}\alpha$ spectrometer with a passband of $\mathrm{\Delta }\lambda =7\mathrm{pm}$. A high-transmission and narrow-band (about 0.3 nm passband) interference filter is used to eliminate side-lobes. Nowadays, advanced thin film deposition techniques for dielectric materials enable the production of interference filters with passbands of $\mathrm{\Delta }\lambda <0.05\mathrm{nm}$, which can be directly used to observe the cores of strong chromospheric absorption lines.¹⁵

High-resolution imaging with Lyot-Öhman filters becomes challenging because of the low filter transmission, which significantly reduces the photon flux for diffraction-limited imaging. Thus, it becomes difficult to achieve short exposure times of just a few milliseconds, which are required to "freeze" the seeing—a common assumption for image restoration applications such as speckle masking imaging,^{16 –18} speckle deconvolution,¹⁹ and blind deconvolution techniques.^{20 ,21} Nonetheless, the rapid oscillations in the solar atmosphere (ROSA)²² instrument at the 0.7-meter Dunn solar telescope (DST) successfully employs a UBF and an $\mathrm{H}\alpha$ Lyot filter. Dual-channel imagers can mitigate the effects of low photon flux on image restoration. Using two strictly synchronized cameras facilitates to restore the broad- and narrow-band channels of an imaging system simultaneously, benefiting from the high signal-to-noise ratio in the broad-band channel. Thus, the atmospheric turbulence and the seeing conditions can be characterized with high confidence, enabling the restoration of the noisier filtergrams that were recorded, e.g., with Lyot-Öhman filters. The broad-band channel also serves as an anchor for the restoration of the narrow-band images when scanning spectral line profiles.

Instruments for high-spatial resolution imaging belong to the standard equipment of solar telescopes, e.g., the ROSA instrument at DST or the visible broadband imager (VBI)²³ at the 4-meter Daniel K. Inouye Solar Telescope (DKIST).²⁴ Larger telescope apertures impact the optical design of the imagers and pose challenges for image restoration.²⁵ While the light gathering power of a telescope increases proportional to the aperture diameter squared, observing at the diffraction limit opposes this effect. Thus, the number of photons per diffraction-limited pixel is independent of the aperture size. However, the angular size of a diffraction-limited pixel becomes smaller for larger telescope apertures. Image restoration assumes that the observed solar feature does not evolve. Thus, the atmospheric sound speed imposes a limit for the image acquisition time of just a few seconds, i.e., the time for a solar feature to traverse a pixel, which is already hard to meet for observations with the GREGOR telescope. For a telescope such as DKIST, the image acquisition time for image restoration may already become too short to gather sufficient images with independent realizations of the distorted wavefronts. In this article, initial results are presented from the improved High-resolution Fast Imager (HiFI+) at the 1.5-meter GREGOR solar telescope.^{26 –28} The imaging system was designed to monitor the solar photosphere and chromosphere with high spatial and temporal resolution in six wavelength bands. The instrument description includes the optical layout, the sCMOS and CMOS camera systems including control computers and software, and data processing and archiving. The new HiFI+ entered routine observations starting with the first observing semester of 2022.

2.

Optical Design

3.

Camera Systems

The idea to improve the imaging capabilities of the GREGOR solar telescope was closely tied to the remodeling of its optical laboratory. With a new Fabry-Pérot interferometer on the horizon, covering an almost identical wavelength range as the GREGOR Fabry–Pérot Interferometer (GFPI)^{30 ,43}, the decision to discontinue the GFPI became imminent. Currently, the option is explored to adapt the Fabry-Pérot etalons⁴⁴ for imaging spectropolarimetry in the blue part of the solar spectrum, building on an existing design for the blue imaging solar spectrometer (BLISS).⁴⁵ As a result, the two Imager M-lite 2M CMOS cameras of the GFPI and the two Imager sCMOS cameras of the original HiFI^{46 ,47} became available. The purchase of two additional Imager M-lite 2M CMOS cameras with the same specifications as the CMOS cameras of the GFPI facilitates an instrument design with six channels that covers distinct photospheric and chromospheric morphological features in fine detail.

The characteristic parameters of the Imager M-lite 2M CMOS and Imager sCMOS cameras are based on data sheets^{48 ,49} and camera manuals^{50 ,51} provided by the manufacturer of the camera systems, i.e., LaVision GmbH in Göttingen, Germany. Both cameras are operated in global shutter mode. A comparison of both camera systems is provided in Table 2, which also demonstrates that the Imager M-lite 2M CMOS and Imager sCMOS cameras are well adapted to the plate scale and maximum FOV of the red and blue imaging channels, respectively. Only in the Ca ii H channel, a camera with a larger number of pixels covering a larger FOV would be desirable. However, the lower dead time, i.e., the time when no photons are collected during an exposure cycle, and the higher image acquisition rate of the Imager M-lite 2M CMOS camera is advantageous because of the more challenging seeing conditions in the very blue part of the solar spectrum. The coherence length, i.e., the Fried-parameter, scales with $r_0\sim {\lambda }^{6/5}$. The same scaling applies to the coherence angle ${\theta }_0$, i.e., the angular extent of the isoplanatic patch, and the coherence time $t_0$, i.e., the time over which the wavefront tilt in an isoplanatic patch can be assumed to be constant. Thus, an improved statistics of the wavefront variations during a given time interval can be expected of the Imager M-lite 2M CMOS cameras as compared to the Imager sCMOS cameras. A programmable timing unit (PTU)⁵² is installed on all computers, which synchronizes the image capture of the cameras with a precision of 10 ns. Image restoration with MOMFBD requires that the exposure times in both channels are the same.

Table 2

Characteristics of the HiFI+ cameras, which feature fast image acquisition rates suitable for image restoration and detectors adapted to the 100′′-diameter FOV and the diffraction limit of the GREGOR telescope.

The quantum efficiency of the Sony Pregius IMX 174 detector is depicted in Fig. 10. The quantum efficiency is about 58% in the Ca ii H channel, about 59% in the $\mathrm{H}\alpha$ narrow- and broad-band channels, and about 38% in the TiO channels. The full well capacity of a pixel is $32000{\mathrm{e}}^{-}$, which is well adapted for the low light levels encountered with narrow-band filters such as Lyot filters, or even with interference filters with a moderately narrow passband of $\mathrm{\Delta }\lambda \approx 1\mathrm{nm}$, when observing strong chromospheric absorption lines. The Imager M-lite 2M CMOS cameras have a custom camera body, which acts as a heat sink. Since the cameras are continuously running, the heat dissipation via the camera body’s surface is sufficient to keep the detector at a constant temperature. The low read noise of about $6.8{\mathrm{e}}^{-}$ facilitates image restoration using either speckle or blind deconvolution techniques, even when the photon flux is low, e.g., in the umbra of sunspots or when observing in the cores of strong absorption lines. In both cases, the intensity drops by a factor of five or more compared to the quiet Sun and the continuum intensity, respectively.

The quantum efficiency of the Fairchild Imaging CIS2051 detector is depicted in Fig. 10. The quantum efficiency is about 52% in the G-band channel and about 59% in the blue continuum channel. Based just on the quantum efficiency, the CIS2051 detector would be the better choice for imaging wavelengths above 550 nm. However, the larger number of pixels makes the Imager sCMOS cameras the better choice for the blue part of the spectrum because of the smaller size of a diffraction-limited pixel. The detector of the sCMOS cameras is kept at a constant temperature using Peltier cooling and forced air for heat removal. The cameras are turned on just for the observations to prevent wear of the cooling fan, and it takes about 20 min to reach a constant temperature of the detector of about $+5°\mathrm{C}$. Two amplifiers for the low and high bits maximize the dynamic range and minimize the noise in the analog-digital conversions of the sCMOS cameras (cf. Table 2 for a comparison with the Imager M-lite 2M CMOS camera).

Assuming that the observed object does not change in a set of images, image restoration uses information about the noise statistics and about the seeing, which is "frozen" in short-exposure images, to retrieve an approximation of the true object. The dark current of about $6{\mathrm{e}}^{-}{\mathrm{s}}^{-1}$ and $2{\mathrm{e}}^{-}{\mathrm{s}}^{-1}$ for the Sony Pregius IMX 174 and Fairchild Imaging CIS2051 detectors, respectively, is inconsequential for typical exposure times below 10 ms, which is already an upper limit for image restoration considering the evolution timescale of Earth’s turbulent atmosphere. The chip architectures of CMOS and CCD devices differ, whereby CMOS detectors may exhibit a strong pixel-to-pixel dependence on the noise characteristics. However, based on existing experience, the noise filters and noise estimates implemented in speckle and blind deconvolution image restoration algorithms are not affected by this issue. In general, the photon noise will dominate the captured data. However, in dark structures such as sunspot umbrae and strong chromospheric absorption features, and in particular in the cores of spectral lines, the photon flux will be significantly reduced. Thus, the digitized read noise signal in the analog-digital conversions becomes increasingly important, which is, however, very low for this generation of CMOS and sCMOS cameras (Table 2). The dynamic range of the CMOS and sCMOS cameras is about 73 and 83 dB or about 1:4600 and 1:13,600, respectively, which is appropriate for image restoration, especially, considering that a large number of images (typically about 100 frames) is used as input for the image restoration procedures.

The operating system of the camera control computers is Window 10 Pro, and the computer specifications are very similar. Any differences are mainly related to the date of purchase (Table 3). Today’s computer technology makes it possible to record high-cadence, large-format images in real-time from computer memory to hard disk drives (HDDs) for HiFI+ No. 1 and 3 and solid-state drives (SSDs) for HiFI+ No. 2. However, vendor specifications are often not accurate and system integration of mainboard, CPU, RAID controller, disk drives, etc. may result in unexpected conflicts, thus limiting the system performance.

Table 3

Specifications of the three HiFI+ camera control computers. Pixel packing and ROI readout for the Imager M-lite 2M cameras are already considered in the actual data transfer rates to RAID 0 storage. The number of image pairs that can be stored already includes additional space for calibration data, i.e., the observing time refers to the duration of uninterrupted science observations excluding time for taking calibration data.

The CPU, mainboard, and other hardware components of the camera control computers were selected in such a way that on one hand sufficient PCIe lanes are available for graphics card, 10 Gigabit Ethernet card, RAID controller, PTU, and camera interface boards and on the other hand to have the highest possible computing power for real-time processing and evaluation of the data. The latter features are needed for camera alignment, calibration, and setting up optimized observing sequences. An external PTU with a USB 2.0 compliant interface had to be used because two dual-port CameraLink interface boards are used with the Imager sCMOS cameras. Another selection criterion is the performance during recording. Here CPU, mainboard, RAM, and disk drives/RAID system must be coordinated to ensure the maximum camera rate even with multicamera systems. The PassMark CPU benchmarks listed in Table 3 for multi- and single-core applications give an indication of the computing power, even though performance benchmarks are highly application specific. The DaVis camera control and imaging software⁵³ uses multithreading for streaming the image sets to RAID 0 storage. The best daytime seeing conditions at Observatorio del Teide are encountered about one hour after sunrise and last for about 1 to 2 h. On exceptional days, periods of very good to excellent seeing extend to about four hours. Furthermore, sometimes good seeing conditions occur a few hours before sunset. The RAID 0 storage of all HiFI+ camera control computers is well adapted to exploit the periods of good to excellent seeing conditions.

Observations at the GREGOR solar telescope can be carried out either remotely using remote access and remote control software or on-site. A trained operator controls the telescope⁵⁴ and the GREGOR adaptive optics system (GAOS).^{55 ,56} HiFI+ is offered as a facility instrument and users are expected to operate the instrument after training. Therefore, an intuitive graphical user interface (GUI) is needed that supports the user to implement and carry out the observing sequences for calibration and science data. In 2022, many experienced observers and novice users worked with the GUI of the DaVis software (Fig. 11) and were able to carry out their observations after one day of training by AIP staff members. A detailed description of HiFI+ and its operations is provided in a comprehensive user manual, and more detailed information is provided in LaVision’s manuals and data sheets for soft- and hardware. The main idea behind the DaVis GUI is to separate device control from displaying images in real-time and image processing. These functions are placed side-by-side in Fig. 11. However, windows, tools, and functions can be arranged in different ways, and they can be shown or hidden so that the user can optimize the GUI layout depending on personal preferences and the type of observations being carried out. The HiFI+ user manual is continuously updated to incorporate best practices and user input.

4.

Life Cycle of High-resolution Imaging Data

5.

Science Verification and First-light Observations

Science verification comprised six observing days during the April 4, 2022 to 8 and 11 time period. The first two days were cloudy—actually the observatory was engulfed in clouds while a low pressure system moved through. On April 6, 2022, the first science data were taken with HiFI+. The seeing conditions were good with a Fried-parameter $r_0\approx 5-10\mathrm{cm}$, and the wind speed was below $5\mathrm{m}{\mathrm{s}}^{-1}$. The seeing conditions on April 7, 2022, were good and occasionally very good with $r_0\approx 5-15\mathrm{cm}$ and with wind speeds of up to $15\mathrm{m}{\mathrm{s}}^{-1}$. On April 8, 2022, the seeing deteriorated because of low wind speeds below $3\mathrm{m}{\mathrm{s}}^{-1}$. The seeing was good with a Fried-parameter $r_0\approx 6-10\mathrm{cm}$. Wind speeds above $5\mathrm{m}{\mathrm{s}}^{-1}$ prevent warm air to accumulate within the concavity of the retracted dome, which leads to telescope seeing close to the primary mirror. Finally, no observations were taken during the last day of the campaign because of bad seeing conditions.

Various solar activity features are displayed in Figs. 13 Fig. 14 Fig. 15 Fig. 16 Fig. 17–18, which were observed on April 7 and 8, 2022, where a total of 378, 1159, and 1084 and 379, 891, and 827 datasets were recorded with the three HiFI+ camera systems, respectively. Targets with different photospheric and chromospheric morphology were chosen, and a selection of those is depicted for all six wavelength channels, whereby the observing time is the same within a few seconds. The images are displayed using histogram clipping to increase the contrast for better display. Some artifacts are visible in the dark umbra of the sunspot, which was observed close to the solar limb. They arise when the mosaic of isoplanatic patches is assembled after image restoration. If the light level is low, then the alignment of the patches may not be perfect. In addition, the signal-to-noise ratio is small in the darkest part of the umbra so that small intensity differences show up as artifacts in the histogram-clipped images.

To further illustrate the quality of the restored images, Fig. 19 provides a collage of all six imaging channels showing the subarcsecond structure of a micropore.⁶³ The FOV of ${10}^{\prime \prime }<span\; class="naked\_sign">\times </span><span\; class="naked\_aural">ばつ</span>{10}^{\prime \prime }$ exhibits in the neighborhood of the micropore a multitude of small-scale brightenings, which are often aligned in chains within the intergranular lanes. The most notable brightenings occurs at the top-right border of the micropore in the Ca ii H image, where filigran fibrils arch away from the micropore. These brightenings are also prominently seen in the broad-band $\mathrm{H}\alpha$ image, where mainly the inner line wings of the $\mathrm{H}\alpha$ absorption line contribute to the emergent intensity. A small bright kernel is even evident in the $\mathrm{H}\alpha$ broadband image, indicating that the bright structure extends to the upper chromosphere. Hints of the brightenings can also be detected in the G-band images, whereas the blue continuum and TiO images only show an inconspicuous small-scale feature at this location. Being able to trace structures through different photospheric and chromospheric layers is a primary goal of HiFI+, as demonstrated in this example of a micropore.

The GREGOR AO system provides the Fried-parameter $r_0$ as a measure of seeing quality. The $r_0$ values are derived from the variance of the total mode wavefront error measured by the AO wavefront sensor.⁶⁴ The Fried-parameter $r_0$ and other environmental parameters are available online (status.tt.iac.es/logs). Measurements of the Fried-parameter $r_0$ taken with different instruments and computed with different methods, even when taken at the same site and at the same time, will show significant deviations. Thus, the following discussion is not generally applicable to other solar telescopes. Based on experience at the GREGOR solar telescope, image restoration becomes possible for a Fried-parameter $r_0\approx 6\mathrm{cm}$ if the AO can lock on a high-contrast feature such as a pore or the umbra of a small sunspot. Restored images may, however, exhibit restoration artifacts in the periphery of the FOV. Locking on quiet-Sun regions requires a Fried-parameter $r_0\approx 8-10\mathrm{cm}$. In this case, most of the images in a time-series can be successfully restored. The transition to excellent seeing conditions occurs at a Fried-parameter $r_0\approx 12-15\mathrm{cm}$. In this case, time-lapse movies of restored images are free of restoration artifacts and are essentially diffraction limited. The best seeing conditions with a Fried-parameter of $r_0=31.7\mathrm{cm}$ were encountered on September 10, 2022, which resulted in a much superior image quality compared with the science verification data shown in this article.

6.

Conclusions

This reference article describes HiFI+ in its configuration in December 2022 at the end of the 2022 observing season. Science verification commenced in April 4 to 11, 2022, as reported in the previous section, which demonstrated that HiFI+ performed according to expectations. The feedback from users in 18 observing campaigns so far was positive. Occasionally reported, synchronization problems of one camera system were solved by a hardware reconfiguration of the PTU. In addition, the RAID 0 HDD storage of two camera control computers was increased by a factor of four. Thus, daily observations are no longer time-limited and cover the time periods with good seeing conditions.

During the 2022A/B observing semesters, i.e., April 6, 2022 to December 2, 2022, HiFI+ data were recorded on 62 days, which resulted in about 90,000 datasets of $2<span\; class="naked\_sign">\times </span><span\; class="naked\_aural">ばつ</span>100$ frame-selected images, i.e., in total about 18 million science images were stored in the GREGOR archive at AIP and about 90 million science images were recorded with HiFI+. In three cases, all data were kept without frame selection because of excellent seeing conditions on one day and two major flares on the other days. Using the computing resources available at AIP, time-series of images were restored for 14 observing days (HiFI+ Level 2 data). This includes about 52,000 images from all six imaging channels restored with the speckle masking technique and about 20,000 $\mathrm{H}\alpha$ narrow- and broad-band images, where image pairs were restored simultaneously using MOMFBD. The grand total of all science and calibration data for the 2022 observing season amounts to about 130 TB.

At the moment, only calibrated HiFI+ Level 1 images are provided in the GREGOR GFPI, HiFI, and HiFI+ data archive at AIP (gregor.aip.de), which provides a common research environment (CRE)⁴⁶ for users of these instruments. These data are embargoed for one year, two years for data related to PhD projects, before they become publicly available. Currently, a bottleneck is the computational effort for image restoration so that only selected datasets can be restored. Restoring a typical HiFI+ dataset for one observing day and for two-synchronized cameras takes 1 to 4 weeks, depending on the duration of the time-series and the chosen image restoration method. Image restoration is typically carried out on desktop computers with AMD Ryzen 9 3950X/5950X CPUs and 64 to 128 GB RAM. In addition, three dedicated computing servers are available with AMD Ryzen 9 3970X($2<span\; class="naked\_sign">\times </span><span\; class="naked\_aural">ばつ</span>$)/AMD EPYC 7713 CPUs and 256 GB RAM. An estimate based on the number of restored images so far is that about 40% of the observed data can be restored with the currently available computing resources at AIP. First Level 2 data will become progressively available to the public starting in the second quarter of 2023. Thus, real-time image restoration is an option, which was considered early on for large research infrastructures such as DKIST, where more computing resources are available, delivering data to a Data Center and Archive.⁶⁵ However, all things considered, principal investigators of an observing campaign should be able to restore their data themselves using available codes for speckle techniques and blind deconvolution. Fortunately, image restoration based on machine learning techniques is a rapidly evolving field of research, e.g., improving the spatial resolution of solar full-disk images⁶⁶ and restoration of high-resolution solar images.⁶⁷ Thus, advances in image restoration are expected to lower the computational burden.

In summary, HiFI+ successfully completed commissioning, science verification, and the first observing season as a facility instrument at the GREGOR solar telescope. Data processing of HiFI+ Level 1 data was completed and Level 2 data processing is well underway. First, scientific publications are currently being prepared, and publicly available data will be progressively released starting in the second quarter of 2023.

Acknowledgments

The 1.5-meter GREGOR solar telescope was built by a German consortium under the leadership of the Leibniz Institute for Solar Physics (KIS) in Freiburg with the Leibniz Institute for Astrophysics Potsdam (AIP), the Institute for Astrophysics Göttingen, and the Max Planck Institute for Solar System Research (MPS) in Göttingen as partners, and with contributions by the Instituto de Astrofsica de Canarias (IAC) and the Astronomical Institute of the Academy of Sciences of the Czech Republic (ASU). The HiFI+ data processing benefits from computational resources, i.e., computing servers, backup server, and Dell Isilon data storage, on-site provided by KIS. We thank AIP’s Technical, Project Management, and IT Services sections for their contributions to HiFI+. In addition, we acknowledge the institutional support of all partners and thank all our colleagues who worked hard in recent years to make GREGOR a better telescope. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. This study was supported by grants DE 787/5-1, VE 1112/1-1, and KO 6283/2-1 of the Deutsche Forschungsgemeinschaft (DFG), grant 57546881 of the Deutscher Akademischer Austauschdienst (DAAD), and by the European Commission’s Horizon 2020 Program under grant agreements 824064 (ESCAPE – European Science Cluster of Astronomy and Particle Physics ESFRI Research Infrastructures) and 824135 (SOLARNET – Integrating High Resolution Solar Physics). CK received funding of the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 895955. We would like to thank the two anonymous reviewers who provided helpful comments and advice improving the manuscript. Thomas Seelemann is employed by LaVision GmbH in Göttingen, where the Imager sCMOS and Imager M-lite 2M cameras, the camera control computers, and the DaVis software were purchased. Beyond this, the authors have no other conflicts of interest to declare that are relevant to the content of this article.

Carsten Denker is head of the "Solar Physics" section and the solar observatory "Einstein Tower" at the Leibniz Institute for Astrophysics Potsdam (AIP) and adjunct professor at the University Potsdam. He holds a doctoral degree in physics and a diploma in social sciences from the University of Göttingen. He is the instrument PI of GFPI, HiFI+, and FaMuLUS. His research efforts concentrate on solar magnetic fields and activity, sunspots, space weather, imaging spectropolarimetry, and image restoration.

Meetu Verma is a post-doctoral researcher in the "Solar Physics" at the Leibniz Institute for Astrophysics Potsdam (AIP). She received her doctoral degree in physics from the University Potsdam in 2013. Thereafter, she worked for one year as a post-doctoral researcher at Max Planck Institute for Solar System Research in Göttingen. Her research interests cover high-resolution studies of solar magnetic features using multi-instruments and multi-wavelength observations. She has extensive experience in organizing coordinated observing campaigns.

Aneta Wiśniewska is a post-doctoral researcher in the "Solar Physics" at the Leibniz Institute for Astrophysics Potsdam (AIP). She holds a doctoral degree in natural sciences from the University of Freiburg, which she gained while working at the Leibniz Institute for Solar Physics (KIS). Her research focuses on helioseismology, global magnetic activity of the Sun, solar flares, space weather, image correction, signal analysis, and spectroscopic observations.

Robert Kamlah is a doctoral student in the "Solar Physics" section at the Leibniz Institute for Astrophysics Potsdam (AIP). He started his doctoral studies in spring 2020, and his research focuses on photospheric and chromospheric magnetic and flow fields. The emphasis of his research project is on analyzing three-dimensional flow fields of emerging and decaying active regions.

Ioannis Kontogiannis is a post-doctoral researcher in the "Solar Physics" section of the Leibniz Institute for Astrophysics Potsdam (AIP). He holds a doctoral degree in natural sciences from the National and Kapodistrian University of Athens, Greece. He is leading two research projects, funded by DAAD/IKYDA and DFG. His research focuses on the dynamics of the quiet Sun (small-scale magnetism, chromospheric structures, and waves), the prediction of solar flares and the evolution of solar active regions.

Ekaterina Dineva is a junior post-doctoral researcher in the "Solar Physics" section at the Leibniz Institute for Astrophysics Potsdam (AIP). She holds a doctoral degree in astrophysics from the University Potsdam and a diploma in business management from the University of National and World Economy, Bulgaria. Her research topics are long- and short-term solar activity, solar cycles, Sun-as-a-star spectroscopy, and solar-stellar connections. Furthermore, she has experience in the field of solar radio physics and space weather.

Jürgen Rendtel is a technical staff member in the "Solar Physics" section at the Leibniz Institute for Astrophysics Potsdam (AIP). He received his doctoral degree in physics from the University Potsdam. He is involved in research and development of instruments for high-resolution solar physics at AIP and responsible for the optical laboratory at the solar "Einstein Tower." He is a founding member of the International Meteor Organization (IMO), where he served as the President for 25 years.

Svend-Marian Bauer is a mechanical engineer in the Technical Section at the Leibniz Institute for Astrophysics Potsdam (AIP) and has a Dipl.-Ing (FH) degree in the field of precision engineering. He participated in national and international projects focusing on astronomical post-focus instrumentation: multi-object spectrograph MUSE for the European Southern Observatory (ESO), high-resolution spectrograph PEPSI at the Large Binocular Telescope (LBT) at Mt. Graham in Arizona, and STELLA robotic telescopes for stellar activity and GREGOR Solar Telescope in Tenerife.

Mario Dionies is a member of the technical staff at the "IT Services" of the at the Leibniz Institute for Astrophysics Potsdam (AIP). His expertise is in information security and the installation and configuration of Windows systems including network components, backup management, and data protection.

Hakan Önel is head of the "Technical Section" at the Leibniz Institute for Astrophysics Potsdam (AIP). He holds a doctoral degree in astrophysics from the Potsdam University and has been involved in the designing, manufacturing, maintenance, verification, and commissioning activities of predominantly ground-based focal instruments as well as instruments for space missions as Solar Orbiter.

Manfred Woche obtained his diploma in physics at the Friedrich Schiller University Jena in 1976. Until 1996, he was employed at the Karl Schwarzschild Observatory Tautenburg. From 1996 until 2001, he worked in optical design and astronomical instrumentation for different institutes, especially for the Max Planck Institute for Extraterrestrial Physics Garching and the Skinakas Observatory Crete. Since 2001, he has been responsible for the optical design of astronomical instrumentation at the Leibniz Institute for Astrophysics Potsdam (AIP).

Christoph Kuckein is a post-doctoral researcher funded by a Marie Skłodowska-Curie fellowship since September 2021 at the "Solar Physics" group of the Instituto de Astrofísica de Canarias (IAC). He holds a doctoral degree in astrophysics from the University of La Laguna (Spain) and worked for about 9 years at the Leibniz Institute for Astrophysics Potsdam (AIP). His research is mainly focused on the interpretation of chromospheric phenomena using inversion tools and spectropolarimetric data.

Thomas Seelemann studied physics at the Georg August University Göttingen. For his diploma thesis and doctoral dissertation, he worked at the Max Planck Institute for Fluid Dynamics in Göttingen in the field of molecular physics and received his doctoral degree in 1980. Since then, he has been employed at LaVision GmbH in Göttingen, where he works on cameras and their integration into dedicated experimental applications.

Partha S. Pal is an associate professor in the Department of Physics, Bhaskaracharya College of Applied Sciences, University of Delhi, India, where he teaches physics and mathematics. He received his doctoral degree in physics from the University of Delhi in 2010. His current research interests cover digital image analysis, statistical analysis, and machine learning in astronomy and astrophysics. He was visiting scientist in the "Solar Physics" at the Leibniz Institute for Astrophysics Potsdam (AIP) from 2018 to 2022.