Images Of Corona Research Articles

A Novel Technique for the Extraction of Dynamic Events in Extreme Ultraviolet Solar Images

High-spatial-resolution images of the solar corona acquired in the extreme ultraviolet (EUV), most notably with the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO) reveal the abundance of dynamic events which range from flaring bright points and jets to erupting prominences and coronal mass ejections (CMEs). In this work we present novel techniques to extract such dynamic events from the more steady background corona using 17.1 nm SDO-AIA images. The techniques presented here treat any time series of coronal images as a matrix that can be decomposed into two matrices representing the background and the dynamic component, respectively. The latter has the properties of a so-called sparse matrix, and the proposed methods are classified as methods based on sparse representations. The proposed methods are the median-filter method, the principal component pursuit, and the dynamic-mode decomposition, all of which include data pre-processing using the noise-adaptive fuzzy equalization method. The study reveals that the median-filter method and the dynamic-mode decomposition enhance all motions in the time series and produce similar results. On the other hand, the principal component pursuit enables the clear differentiation of CMEs from the background corona, thus providing a valuable tool for the characterization of their acceleration profiles in the low corona as seen in the EUV.

Archaeological cognition of the Eastern mausoleum of Qin state using integrated space-ground observation tools

The Eastern Mausoleum of Qin State is a significant component of the Qin Dynasty's royal tombs, reflecting the social development level during the Warring States period (475 BC ~ 221 BC) in China. At the onset of our investigation, we mapped the site's boundaries utilizing Corona satellite imagery and employed the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Moisture Index (NDMI) to identify archaeological features. Additionally, this study is the first to propose the use of thermal infrared band data from the SDGSAT-1 satellite to explore thermal archaeological traces, demonstrating their viability for archaeological site analysis. Subsequently, electromagnetic (EM) prospection was utilized to validate the presence of an ancient burial chamber passage. Landscape monitoring and analysis of the No.1 Mausoleum were performed using Corona and Google Earth images, revealing the accuracy of the Geomancy Theory of Chinese mausoleums through dynamic remote sensing of surface changes. Furthermore, our employment of space-to-ground observational modalities and resultant Digital Elevation Models (DEM) have been used to provided new insights into the application of Remote Sensing (RS) and Geomancy in archaeology, thereby emphasizing the pivotal role of site selection in heritage preservation. This research underscores the promise of synergistic space-ground observations in both exploiting the archaeological riches of cultural heritage sites and ensuring the enduring conservation of these irreplaceable patrimonial assets.

Deep learning-based detection of qanat underground water distribution systems using HEXAGON spy satellite imagery

Qanats are a remarkable type of ancient hydraulic structure for sustainable water distribution in arid environments that use subterranean channels to transport water from highland or mountainous areas. The presence of the qanat system is marked by a line of regularly spaced shafts visible from the surface, which can be used to detect qanats using satellite imagery. Typically, qanats have been documented by field mapping or manual digitisation within a Geographic Information System (GIS) environment. This process is time-consuming due to the numerous shafts within each qanat line. However, several automated methods for detecting qanat structures have been explored, using techniques such as morphological filters, custom convolutional neural networks (CNN) and, more recently, YOLOv5 and Mask R-CNN. These approaches used high-resolution RGB images and CORONA images. However, the use of black and white CORONA in CNNs has been limited in its applicability due to a high rate of false positives.This paper explores the potential of YOLOv9 in processing the black and white HEXAGON (KH-9) high-resolution spy satellite system launched in 1971. Two areas in Afghanistan (Maiwand) and Iran (Gorgan Plain) were selected to train the system images extracted from HEXAGON imagery and artificial synthetic data. The training dataset was augmented using the Albumentation library, which increased the number of tiles used. The model was tested using two types of HEXAGON imagery for selected areas in Afghanistan (Maiwand), Iran (Gorgan Plain) and Morocco (Rissani), and CORONA imagery in Iran (Gorgan Plain).Our study provided a model capable of predicting the location of qanat shafts with a precision of over 0.881 and a recall of 0.627 for most of the case studies tested. This is the first case study aimed at detecting qanats in different landscapes using different types of satellite imagery. Using real, augmented, and artificial data allowed us to generalise the representation of qanats into lineal groups of circular features. Thanks to applying labelling for individual qanats and their pairs as separate classes, our approach eliminated most of the isolated and clustered false positives.

How natural are the forests in Rajiv Gandhi (Nagarhole) Tiger Reserve? A multi-source data approach.

This study aimed to monitor long-term land use dynamics for understanding the natural forestintegrity and intactness of the Rajiv Gandhi (Nagarhole) Tiger Reserve (RTR) pre- and post-declarations as TR. We employed multi-source data from Survey of India Toposheets (1:50k), Landsat-7, and Sentinel-2A along with Global Ecosystem Dynamics Investigation (GEDI) vegetation canopy height (10m) data, a high-spatial resolution CORONA (1970) images and temporal Google Earth Pro images for mapping and validation. To map vegetation type, land use and land cover (LULC) transitions, and fragmentation (1980-2022) we employed a hybrid classification approach. This study also analyzed decadal forest dynamics within TRsusing India's State of Forest Reports (ISFR). Findings reveal significant forest fragmentation and habitat loss due to anthropogenic activities in the TR. Mono-plantations (teak and eucalyptus) were found inside TR, while the buffer (1km) was occupied mainly with coffee and orange plantations which indicates the prevalence of human footprint. The overall accuracy of the current period (2022) is 92.0% with a kappa coefficient value of 0.90. These plantations were established during the British colonial period (early 1900s) for commercial purposes by clearing natural forests. The present study highlights that mono-plantations have not transitioned into natural forests even after a century. This lack of transformation could potentially compromise the integrity of the native forest. Despite its ecological significance, RTR has experienced disturbance due to human footprint. Hence, there is a need for an action plan to protect this vital landscape by replacing mono-plantations with suitable species to preserve the integrity of the forest. These issues extend beyond the protected areas, impacting surrounding regions and require regular monitoring. The proposed methods can be applied to other protected areas facing similar problems in the countryand world.

Observation of solar energetic particles with Metis on board Solar Orbiter on February 25, 2023

The Solar Orbiter Metis coronagraph captures images of the solar corona in both visible (VL) and ultraviolet (UV) light. Tracks ascribable to the passage of galactic and solar particles appear in the Metis images. An algorithm implemented in the Metis processing electronics allows us to separate the pixels fired by VL photons from those crossed by high-energy particles. These spurious pixels are stored in cosmic-ray matrices that can be visually analyzed for particle monitoring deep into the spacecraft's interior. This algorithm has been enabled for the VL instrument only, since the process of separating the particle tracks from pixels fired by photons in the UV images was shown to be quite challenging with respect to a quantitative analysis. This work is aimed at studying galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the Metis cosmic-ray matrices in February 2023. We compared a visual analysis of Metis cosmic-ray matrices gathered on February 22, 2023, with GCRs only, and on February 25, 2023 with both GCRs and SEPs, to Monte Carlo simulations of the VL instrument during the same days. We estimated the solar modulation parameter associated with the GCR proton energy spectrum in February 2023. We show that Metis plays the role of monitoring galactic and solar protons. The Metis particle observations are used for the diagnostics of the VL instrument performance and to study the spacecraft inner charging from solar minimum towards the next solar maximum. These achievements have been attained with the benefit of the joint observations of Metis, the Energetic Particle Detector/High Energy Telescope, and near-Earth and Earth-based instruments.

Identifying urban built-up areas using CORONA imagery in the pre-Landsat era: a case study of Shanghai in 1965

ABSTRACT The Corona project (1959–1972) created a large number of high-resolution images that provided valuable historical research data before the advent of Landsat (1972) and even compensated for the lack of accuracy in early stages. In this study, we collected eight available Corona images to create a historical remote sensing image of Shanghai in the 1960 and developed an automatic image segmentation and classification methodology. In the experimental part, we verified its accuracy, and discussed the urbanization process in Shanghai. The results showed that 1) In 1965, the urban area of Shanghai was mainly distributed in Puxi, and the urbanization degree of the entire hinterland of Pudong was still very low. Built-up areas were highly concentrated in the main urban areas. 2) The overall accuracy was 91.5% and the kappa coefficient was 0.762. 3) We compared the built-up area in 1965 with the current urban area, which increased from 306.23 to 2,804.25 km2. Besides, historical imagery also captured the state of environmental pollution at that time. Overall, our method could inform the mapping and classification of remotely sensed land surfaces on a global scale in the 1960s, extending pre-Landsat era research to studies of urban history, archaeology and cultural heritage.

Propagation Properties of Sunspots Umbral Oscillations in Horizontal and Vertical Directions

We present a study on investigating the propagation characteristics of umbral oscillations in sunspots. In sunspot 1 (located in NOAA AR 12127) with four umbrae, the analysis shows that the oscillations in different umbrae are correlated. The weak correlation (<20%) is attributed to the propagation of umbral oscillations across the umbral boundary to its adjacent umbra in the horizontal direction. We speculate that oscillations in two of the umbrae have a common origin in the sub-photosphere, resulting in a stronger correlation (>30%). Additionally, utilizing the TiO (photosphere), Hα (chromosphere) images provided by BBSO/GST, and the 304 Å (upper chromosphere and lower transition region), 171 Å (upper transition region), 193 Å (corona), and 211 Å (active region corona) images acquired by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO), we analyze the vertical propagation of oscillations in the sunspot umbra. Multi-channel observation shows that the umbral oscillations observed in the lower atmosphere of sunspot 1 cannot be detected in the upper atmosphere. However, in sunspot 2 (located in NOAA AR 12132), oscillations in the lower atmosphere can propagate to the upper atmosphere. Using photospheric magnetic field data provided by the Helioseismic and Magnetic Imager on board SDO, potential field extrapolation of the magnetic field for the two sunspots shows that open magnetic field structures allow sunspot oscillations to propagate to higher heights, while closed magnetic field structures do not.

2OC: A General Automated Orientation and Orthorectification Method for Corona KH-4B Panoramic Imagery

Due to a lack of geographical reference information, complex panoramic camera models, and intricate distortions, including radiation, geometric, and land cover changes, it can be challenging to effectively apply the large number (800,000+) of high-resolution Corona KH-4B panoramic images from the 1960s and 1970s for surveying-related tasks. This limitation hampers their significant potential in the remote sensing of the environment, urban planning, and other applications. This study proposes a method called 2OC for the automatic and accurate orientation and orthorectification of Corona KH-4B images, which is based on generalized control information from reference images such as Google Earth orthophoto. (1) For the Corona KH-4B panoramic camera, we propose an adaptive focal length variation model that ensures accuracy and consistency. (2) We introduce a robust multi-source remote sensing image matching algorithm, which includes an accurate primary orientation estimation method, a multi-threshold matching enhancement strategy based on scale, orientation, and texture (MTE), and a model-guided matching strategy. These techniques are employed to extract high-accuracy generalized control information for Corona images with significant geometric distortions and numerous weak texture areas. (3) A time-iterative Corona panoramic digital differential correction method is proposed. The orientation and orthorectification results of KH-4B images from multiple regions, including the United States, Russia, Austria, Burkina Faso, Beijing, Chongqing, Gansu, and the Qinghai–Tibet Plateau in China, demonstrate that 2OC not only achieves automation but also attains a state-of-the-art level of generality and accuracy. Specifically, the standard deviation of the orientation is less than 2 pixels, the mosaic error of orthorectified images is approximately 1 pixel, and the standard deviation of ground checkpoints is better than 4 m. In addition, 2OC can provide a longer time series analysis of data from 1962 to 1972, benefiting various fields such as environmental remote sensing and archaeology.

Steadiness of Coronal Heating

The EUI instrument on the Solar Orbiter spacecraft has obtained the most stable, high-resolution images of the solar corona from its orbit with a perihelion near 0.4 au. A sequence of 360 images obtained at 17.1 nm, between 2022 October 25 19:00 and 19:30 UT, is scrutinized. One image pixel corresponds to 148 km at the solar surface. The widely held belief that the outer atmosphere of the Sun is in a continuous state of magnetic turmoil is pitted against the EUI data. The observed plasma variations appear to fall into two classes. By far the dominant behavior is a very low amplitude variation in brightness (1%) in the coronal loops, with larger variations in some footpoint regions. No hints of observable changes in magnetic topology are associated with such small variations. The larger-amplitude, more rapid, rarer, and less well organized changes are associated with flux emergence. It is suggested therefore that while magnetic reconnection drives the latter, most of the active corona is heated with no evidence of a role for large-scale (observable) reconnection. Since most coronal emission-line widths are subsonic, the bulk of coronal heating, if driven by reconnection, can only be of tangentially discontinuous magnetic fields, with angles below about 0.5c S /c A ∼ 0.3β, with β the plasma beta parameter (∼0.01) and c S and c A the sound and Alfvén speeds, respectively. If heated by multiple small flare-like events, then these must be ≲1021 erg, i.e., picoflares. But processes other than reconnection have yet to be ruled out, such as viscous dissipation, which may contribute to the steady heating of coronal loops over active regions.

On a ~210 t Caribbean coastal boulder: The huracanolito seaward of the ruins of the Bucanero resort, Juragua, Oriente, Cuba

AbstractCoastal boulder deposits (CBDs), named huracanolitos in Cuba, found along rocky shores, result from storms, tropical cyclones or tsunamis. Despite being important indicators for coastal hazard assessment, determining the mode of emplacement of CBDs (storm/hurricane or tsunami) is not easy. We present, for the first time in English, data about CBDs along the shores of the Cuban Archipelago. More specifically, we focused on a CBD, that is, to our knowledge, the largest one ever described on Cuba Island. Located on a low‐lying coral reef terrace on the SE shore of the island, the reefal limestone CBD is emplaced seaward of the ruins of the Bucanero resort. The resort was built in 1989, endured hurricanes Ivan (2004) and Dennis (2005) and, in October 2012, was destroyed by Hurricane Sandy. As observed on Corona and Landsat satellite images since 1962, the CBD was not moved, neither by hurricane Flora (1963) nor Sandy (2012), both associated with important storm surges and powerful swells. We determined the CBD volume with open‐source structure from motion photogrammetry as 82.6 m3. Then, we estimated from a sample its density as 2550 kg/m3. Finally we calculated its weight as 210.6 tons. We calculated the minimum flow velocity responsible for the emplacement of the CBD 33 ± 2 m inland—6.83 ± 0.54 m/s and 7.26 ± 0.51 m/s. Such flow velocities are compatible with those of both tsunamis and hurricanes. Because of the greater frequency of hurricanes than tsunamis in the area, we propose that a tropical cyclone generated the extreme surge and wave that emplaced the Bucanero CBD. Such CBDs demonstrate that on Cuba's south coast, we can expect marine flooding exceeding the flooding during the major hurricanes of recent decades.

Telecoupled urban demand from West African cities causes social-ecological land use transformation in Saharan oases.

Little is known about the long-distance telecoupling effects of urban food demands on land use changes (LUCs) in remote oases of the Southern Sahara. Using the example of two typical oasis settlements on Mont Bagzam in the southern Aϊr Mountains of Niger which are linked to regional and global markets by an unpaved road since 2015, this study aimed at analyzing time trajectories of LUCs and related changing agricultural production patterns. LUCs were quantified for 1955 to 2022 using GIS-based mapping of agriculture and natural vegetation based on historical aerial photographs, CORONA and multi-spectral satellite images, and high resolution drone-based surveys. The results show a major increment in actively used agricultural land in the 850 ha watershed of the two oases from 11 ha in 1955 to 13 ha in 2003 and 68 ha in 2022 as well as the addition of 92 irrigation wells to 16 existing ones between 2003 and 2022. LUCs and evapotranspiration calculated from climatic data of a local weather station allowed to estimate changes of irrigation water needs in the selected watershed. While annual precipitation averages only 214 mm, local reference evapotranspiration may reach 1,476 mm year-1. Therefore, the additional annual irrigation water needs for the newly established fields between 2003 and 2022 cultivated to cash crops rose by 696 million l. To detect LUC effects on soil quality, soil samples of onion and garlic fields of different ages were collected employing a false-time-series approach. Results reveal increasing soil pH and salt concentrations and falling ground water tables, which reflects a negative water balance and ground water extraction above recharge levels. Our study provides evidence that the newly established telecoupled production systems on Mont Bagzam threaten the sustainability of existing local agricultural production and related livelihoods of agro-pastoralists.

Monitoring rural-urban transformation in the coastal region of Rabat-Sale-Kenitra, Morocco.

Worldwide urbanization drives rural-urban transformation (RUT) which has major consequences in many countries of the Global South where there is an urgent need to better understand and manage the underlying processes and consequences for ecosystem services. To fill existing knowledge gaps on the extent and time course of RUT in Morocco, this study focused on (i) analyzing the spatial patterns of rural-urban transformation in the Rabat-Sale-Kenitra (RSK) region from 1972 to 2020, (ii) identifying key mechanisms of change, and (iii) defining the main driving forces behind the spatial transformation patterns. To this end, we processed data of the Landsat free archive, historical grayscale Corona images, and nighttime lights datasets on Google Earth Engine (GEE) using machine learning classifiers and LandTrendr spectral-temporal segmentation algorithms. With an overall accuracy (OA) ranging from 88-95%, the results revealed that during the study period the RSK region experienced a 473% growth of horizontal built-up reflected in an area increase from 63.4 km2 to 299.9 km2. The main changes occurred along the Kenitra-Rabat-Temara axis and in central cities connected to the main road network. The horizontal expansion of large and medium-sized cities led to the formation of a Rural-Urban Interface (RUI) on the outskirts. The urban sprawl of some cities has affected the surrounding rural lands within the RUI. Environmental, social, economic, and political forces have interacted in shaping the changes in rural-urban landscapes.

In-flight radiometric calibration of the Metis Visible Light channel using stars and comparison with STEREO-A/COR2 data

Context.We present the results for the in-flight radiometric calibration performed for the Visible Light (VL) channel of the Metis coronagraph on board Solar Orbiter.Aims.The radiometric calibration is a fundamental step in building the official pipeline of the instrument, devoted to producing the calibrated data in physical units (L2 data).Methods.To obtain the radiometric calibration factor (ϵVL), we used stellar targets transiting the Metis field of view. We derivedϵVLby determining the signal of each calibration star by means of the aperture photometry and calculating its expected flux in the Metis band pass. The analyzed data set covers the time range from the beginning of the Cruise Phase of the mission (June 2020) until March 2021.Results.Considering the uncertainties, the estimated factorϵVLis in a good agreement with that obtained during the on-ground calibration campaign. This implies that up to March 2021 there was no measurable reduction in the VL channel throughput. Finally, we compared the total and polarized brightness visible light images of the solar corona acquired with Metis and STEREO-A/COR2 during the November 2020 superior conjunction of these instruments. A general good agreement was obtained between the images of these instruments for both the total and polarized brightness.

Study on the Measurement Technique and Judgment Procedure of Ultrasonic Corona Imaging Equipment

Corona discharge is a phenomenon wherein gas on the surface of electrical equipment is ionised. Severe ionisation can lead to insulation breakdown and cause equipment damage. Consequently, non-contact portable devices are employed to detect corona discharge in real time while the electrical equipment is pressurised. Recently, several devices capable of visualising corona discharge phenomena occurring in the ultrasonic region have been developed. However, these devices are primarily used for scanning purposes to verify the occurrence of partial discharge, as detailed guidelines for operating the equipment in real-world field conditions are yet to be established. Therefore, this study proposes a measurement technique for utilising ultrasonic corona imaging diagnostic equipment in the field. This technique involves the use of corona discharge electrodes and aged epoxy insulator samples. First, the performance of the ultrasonic corona imaging diagnostic equipment based on environmental conditions was evaluated by varying the distance, frequency, temperature, and humidity using the corona discharge electrodes. Then, parallel measurements were conducted with a high-frequency current transformer sensor on epoxy insulator samples subjected to simple ageing, cracking, and partial surface damage, and the results were analysed. Finally, an efficient measurement technique, including equipment operation procedures, was proposed by integrating the measurement results.

The SWAP Filter: A Simple Azimuthally Varying Radial Filter for Wide-Field EUV Solar Images

We present the SWAP Filter: an azimuthally varying, radial normalizing filter specifically developed for EUV images of the solar corona, named for the Sun Watcher with Active Pixels and Image Processing (SWAP) instrument on the Project for On-Board Autonomy 2 (PROBA2) spacecraft. We discuss the origins of our technique, its implementation and key user-configurable parameters, and highlight its effects on data via a series of examples. We discuss the filter’s strengths in a data environment in which wide field-of-view observations that specifically target the low signal-to-noise middle corona are newly available and expected to grow in the coming years.

Desertification hazards in the middle zone of Wadi Fatimah, West Saudi Arabia

This research aims at determining and analysing the causes and consequences of desertification in the middle zone of Wadi Fatimah using satellite images, climatic data, and topographic maps. The climatic parameters such as temperature, rainfall, and global reference evapotranspiration (ET0) indicated common severe arid conditions in the study area. The CORONA images acquired in 1967 and 1979 along with the topographic map of 1971 helped define the initial morphologic features and anthropogenic regimes. Analysing the various spatial datasets implied that the inappropriate management of water resources has resulted in changes in the anthropogenic regimes in the middle zone of Wadi Fatimah. These changes have triggered a chain of desertification processes such as degradation of the vegetation biomass and wind activities. These processes have transformed 15.3 km2 of agricultural farms into abandoned lands. Nineteen km2 of bushes have disappeared as well. The degradation of both agricultural and natural vegetation has exposed soils to intense wind erosion that detaches, transports and deposits sand in areas of low elevations. Accordingly, sand accumulations have massively expanded from 16.4 km2, as monitored by 1967 CORONA images, to 40.8 km2, as monitored by SPOT in 2013. This research emphasises that the middle zone of Wadi Fatimah has been experiencing remarkable changes in its morphologic and environmental characteristics in response to serious desertification processes. These processes are strongly linked to many anthropogenic interventions. It became a necessity, then, to redefine, study and assess the various anthropogenic parameters and their relative roles in desertification processes to combat desertification hazards and enhance sustainable environmental context in the middle zone of Wadi Fatimah.

Linking digital image intensity to carrier density in low-pressure corona discharges

The electrification of transportation, and aircraft electrification in particular, is experiencing rapid development due to the more efficient use of energy. Since the dielectric strength of air decreases at the cruising altitudes of commercial aircraft due to the reduced pressure environment, there is a need to control and minimize the risks associated with electrical discharges. This paper shows from experimental and computational data that there is a relationship between the electrical and optical phenomena involved in the discharge process. To this end, this paper analyzes corona discharges generated using different electrode geometries under a wide range of pressures from 100 kPa to 10 kPa. It is shown that the densities of charged particles or charge carriers generated during the discharge process are positively correlated with the intensity of corona images acquired with a digital imaging sensor sensitive to the near UV and visible wavelength ranges. Therefore, the intensity of the images can be used as a reliable and accurate indicator of the corona activity, the values of which are related to the ionization processes involved in the discharges. The results presented in this paper can be applied in various physical and engineering fields, such as high voltage engineering, power line monitoring, or ozone generation, among others.

Trichel pulse characteristics and mechanism of negative corona discharge in sub-millimeter gaps

A negative corona discharge system of a needle-plate electrode suitable for sub-millimeter gaps is established to investigate Trichel pulse characteristics of negative corona discharge, in which an optical acquisition system is especially applied to timely observe a discharging corona. Electrostatics–hydrodynamics coupling simulations of air discharging in 100 μm-gaped needle-plate electrodes are performed to elucidate the micro-physical process of negative corona discharge. The impact ionization coefficient used for simulations and the experimentally recorded images of discharge corona are combined to characterize the active region of secondary electron emission. Dynamical distribution and transport of the charged particles are analyzed from multiphysics simulations to explain the microscopic mechanism for various stages of Trichel pulses. Even though the corona front near the plate electrode maintains a high rate of collision ionization and secondary electron excitation, the needle tip corona has not reached the threshold electric field of electron avalanche required for glow discharge, as manifested by discharge sawtooth waves comprised of corona and glow components. The amplitude and frequency of Trichel pulses increase, respectively, with impact ionization and secondary electron emission, which is evidently dependent on attachment coefficient and anion mobility. A higher attachment coefficient will lead to a significant reduction in amplitude of Trichel pulses. The present study provides a theoretical basis and experimental verification for micrometer discharges, which is the key point of insulation protections in microelectromechanical systems.

Small-scale EUV features as the drivers of coronal upflows in the quiet Sun

Context. Coronal upflows in the quiet Sun are seen in a wide range of features, including jets and filament eruptions. The in situ measurements from Parker Solar Probe within ≈0.2 au have demonstrated that the solar wind is highly structured, showing abrupt and near-ubiquitous magnetic field reversals (i.e., switchbacks) on different timescales. The source of these structures has been associated with supergranular structures on the solar disc. This raises the question of whether there are additional small coronal features that contribute energy to the corona and produce plasma that potentially feeds into the solar wind. Aims. During the Solar Orbiter first science perihelion, high-resolution images of the solar corona were recorded using the Extreme Ultraviolet High Resolution Imager (HRIEUV) from the Extreme Ultraviolet Imager (EUI). The Hinode spacecraft was also observing at the same location providing coronal spectroscopic measurements. Combining the two datasets allows us to determine the cause of the weak upflows observed in the quiet Sun and the associated activity. Methods. We used a multi-spacecraft approach to characterise regions of upflows. The upflows were identified in the Fe XII emission line by the Hinode EUV Imaging Spectrometer (EIS). We then used imaging data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) and the High Resolution Imagers (HRI) from EUI on board the Solar Orbiter to identify coronal features and magnetic field data from the SDO Helioseismic and Magnetic Imager (HMI). Interface Region Imaging Spectrograph (IRIS) observations were also used to understand the photospheric and chromospheric driving mechanisms. Results. We have identified two regions of coronal upflows in the quiet Sun, with respective sizes and lifetimes of (20 Mm2, 20 min) and (180 Mm2, several hours), which are contrasting dynamic events. Both examples show weak flux cancellation, indicating that the source of the upflows and enhancements is related to the magnetic field changes. The first event, a larger upflow region, shows velocities of up to −8.6 km s−1 at the footpoint of a complex loop structure. We observe several distinct extreme ultraviolet (EUV) features including frequent loop brightenings and plasma blobs travelling along closed coronal loops. The second upflow region has velocities of up to −7.2 km s−1. Within it, a complex EUV feature that lasts for about 20 min can be seen. This main feature has several substructures. During its appearance, a clear mini-filament eruption takes place at its location, before the EUV feature disappears. Conclusions. Two features, with contrasting properties, show upflows with comparable magnitudes. The first event, a complex loop structure, shares several similarities with active region upflows. The second one, a complex small-scale feature that could not have been well resolved with previous instruments, triggered a cascade of events, including a mini-filament that lead to a measurable upflow. This is remarkable for an EUV feature that many instruments can barely resolve. The complexity of the two events, including small loop brightenings and travelling plasma blobs for the first and EUV small-scale loops and mini-filament for the second one would not have been identifiable as the sources of upflow without an instrument with the spatial resolution of HRIEUV at this distance to the Sun. These results reinforce the importance of the smallest-scale features in the Sun and their potential relevance for and impact on the solar corona and the solar wind.

Using CORONA Imagery to Study Land Use and Land Cover Change—A Review of Applications

CORONA spy satellites offer high spatial resolution imagery acquired in the 1960s and early 1970s and declassified in 1995, and they have been used in various scientific fields, such as archaeology, geomorphology, geology, and land change research. The images are panchromatic but contain many details of objects on the land surface due to their high spatial resolution. This systematic review aims to study the use of CORONA imagery in land use and land cover change (LULC) research. Based on a set of queries conducted on the SCOPUS database, we identified and examined 54 research papers using such data in their study of LULC. Our analysis considered case-study area distributions, LULC classes and LULC changes, as well as the methods and types of geospatial data used alongside CORONA data. While the use of CORONA images has increased over time, their potential has not been fully explored due to difficulties in processing CORONA images. In most cases, study areas are small and below 5000 km2 because of the reported drawbacks related to data acquisition frequency, data quality and analysis. While CORONA imagery allows analyzing built-up areas, infrastructure and individual buildings due to its high spatial resolution and initial mission design, in LULC studies, researchers use the data mostly to study forests. In most case studies, CORONA imagery was used to extend the study period into the 1960s, with only some examples of using CORONA alongside older historical data. Our analysis proves that in order to detect LULC changes, CORONA can be compared with various contemporary geospatial data, particularly high and very high-resolution satellite imagery, as well as aerial imagery.