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The 5.4 Pohang earthquake occurred on November 15, 2017. It was the second-largest earthquake in South Korea since instrumental earthquake observations began. In this study, the PSInSAR method using Sentinel-1 satellite ascending and descending data were used to analyze the time-series surface displacement of the Pohang area before and after the earthquake. As a result, in the case of PSInSAR result using the descending pass data, surface uplift displacement up to 45 mm in the LOS direction was observed immediately after the earthquake near the epicenter. In addition, to identify the horizontal movement of the co-seismic uplift displacement, it was derived into the vertical component and horizontal component using the results of two different orbital data. And it shows the surface was spreading out into both sides, not just east or west. Besides, continuous subsidence with a velocity of up to 80 mm/year was found in a specific area of the footwall, which was continued before the earthquake. To identify the origin of the subsidence we compared it with the past optical images, and subsidence areas were consistent with the past river topography.

Globally, coal is a major mineral used in energy production, and Coal ash is produced in energy production. Coal ash pollutes the environment and causes health problems for humans. Therefore, it is important to store coal ash, most of the coal ash is stored in landfills. Landfills ground subside over time, and ground subsidence is one of the main factors in landfills stability. Therefore, it is important to understand the stability of coal ash landfills, so we would like to monitor coal ash landfills through remote sensing methods. In this study, the Stanton Energy Center, a coal-fired power plant in Orlando, Florida, in the southeastern United States, was selected as a research area. The Stanton energy center stored coal ash in a landfill next to the power plant and installed solar panels on top of the coal ash landfill in 2017. In this study, the Sentinel-1 satellite provided by the European Space Agency (ESA) was used, and ascending data was obtained between June 2018 and 2022. Digital Elevation Model (DEM) used for image processing used LIDAR DEM images with 1 m spatial resolution provided by the United States Geological Survey (USGS). PSInSAR image preprocessing used SNAP software provided by European Space Agency (ESA), and PSInSAR process used Standard Method of Persistent Scatterers (StaMPS). The PSInSAR result using Copernicus 30 DEM in the coal landfill area confirmed about 50 mm subsidence for 5 years in the LOS direction, and the PSInSAR result using Lidar DEM confirmed about 45 mm subsidence for 5 years in the LOS direction. In addition, the PSInSAR results in a stable area located near the landfill confirmed that there was little subsidence in the LOS direction for 5 years.

The 6th nuclear test of North Korea on September 3, 2017 produced an mb 6.1 artificial earthquake and significant surface deformations detectable from satellite observations. Wang et al. (2018) have reported the surface displacement of the Mt. Mantap caused by the explosion by applying offset-tracking method to TerraSAR-X SAR images. Based on the assumption of elastic behaviour of the mountain body, they have modelled the rise and collapse of the mountain and suggested the location, depth and energy of the explosion. However, we suspect that the surface displacement might be caused by landslide in which case the elastic modelling would be misleading. In this paper, we use both SAR interferometry and offset-tracking method to quantify the elastic and random deformation caused by the explosion. The 3-D displacement vectors around the rim of the explosion, where the inter-ferometric coherence is maintained, were obtained by using three ALOS-2 interferograms acquired in different orbits. Only east-west component of the displacement vector was valid due to orbital characteristics, which indicates the explosive tendency of the bedrock of up to 25 cm in the rim of the mountain. Deformation on the ruptured zone, where the interferometric coherence is lost, was detected through visual inspection and offset tracking by using two pairs of high-resolution ALOS-2 and TerraSAR-X images. It showed up to 3.5 m displacement on the mountain slope towards the direction of gravity, which is similar to the results of Wang et al. (2018). However, we have visually identified many stable points and features that have not moved at all in the mountain flank surrounded by active surface deformation, which is believed to be stable bedrocks and outcrops. This implies that the displacements observed by the offset method in the mountain flank of the ruptured zone were mostly of landslides caused by the topsoil and boulder stones. It is suggested that elastic behaviour of the mountain body due to the 6th nuclear test of North Korea is unidentifiable and the subsequent modelling might be invalid in the mountain flank of the ruptured zone where surface motion from landslides is dominant.

Ground-based synthetic aperture radar (GB-SAR) is a useful tool to simulate advanced SAR systems with its flexibility on RF system and SAR configuration. This paper reports an indoor experiment of bistatic/multistatic GB-SAR operated in Ku-band with two antennae: one antenna was stationary on the ground and the other was moving along a linear rail. Multiple bistatic GB-SAR images were taken with various stationary antenna positions, and then averaged to simulate a multistatic GB-SAR configuration composed of a moving Tx antenna along a rail and multiple stationary Rx antennae with various viewing angles. This configuration simulates the use of a spaceborne/airborne SAR system as a transmitting antenna and multiple ground-based stationary antennae as receiving antennae to obtain omni-directional scattering images. This SAR geometry with one-stationary and one-moving antennae configuration was analyzed and a time-domain SAR focusing algorithm was adjusted to this geometry. Being stationary for one antenna, the Doppler rate was analyzed to be half of the monostatic case, and the azimuth resolution was doubled. Image quality was enhanced by identifying and reducing azimuth ambiguity. By averaging multiple bistatic images from various stationary antenna positions, a multistatic GB-SAR image was achieved to have better image swath and reduced speckle noise.

InSAR coherence detects random surface change that measures the activity or stability of the interferometric phase of InSAR data. Based on InSAR coherence, NDAI (Normalized Difference Activity Index) has been used to detect mining activity in the open pit mine. To remove the noise contained in coherence values, the newly defined NDAI provides only information due to the impact of mining activities. Mining activity analysis was used to understand the annual activity pattern of the mine, and from that to estimate the pushback design. The activities of the March 5 Youth mine took place in a clockwise direction. It was also possible to observe changes around newly formed surroundings, such as where topsoil is loaded or riverbanks This study is well appropriate for mines where site access is not possible. This method can be applied to other open-pit mine.

Musan mine in North Korea is the largest open-pit iron mine in Asia with the proved reserves of about 2.06 billion tons and more than 9 square kilometers. Open-pit mining is one of the surface mining technique extracting minerals from the surface. Vegetation is rarely distributed at the mining site because the topsoil is removed and the ore is mined directly from the surface. Therefore, it is effective to observe surface displacement at the mining site using Interferometric Synthetic Aperture Radar (InSAR) technology. InSAR coherence detects random surface change that measures the activity or stability of the interferometric phase of InSAR data. High coherence will be maintained on the surface where there is no movement and only surface scattering. On the other hand, the surface where there is a lot of movement and volumetric scattering has low coherence value. Therefore, using 12-days InSAR coherence images from Sentinel-1 satellites, for example, it is possible to analyze how active the open-pit mine is during the 12 days. Sentinel-1A satellite images were acquired from June 11, 2015 to May 24, 2016, followed by Sentine-1B satellite images from September 27, 2016 to April 21, 2019. A total of 102 SAR images were downloaded from European Space Agency (ESA) portal. There is a gap between May 24 and September 27, 2016 due to the transition of the data acquisition plan. Over 100 12-days coherence data were obtained by applying InSAR. Stable spots and target spots were selected through average and standard deviation of the entire coherence time series data. Coherence values include not only the mining activity but also the effects of perpendicular baseline, temporal baseline, and weather. Therefore, NDAI (Normalized Difference Activity Index) was newly defined to remove the noise and only the coherence value due to the influence of the mining activity was extracted. The degree of activities can be observed by the time series coherence and NDAI images. This study needs other references related to mining activities in order to analyze the mining activities in more detail. This method can be applied to other open-pit mine.

The dynamics of landfast sea ice, also called fast ice for short, has a large influence on the variability of polynyas and marine ecosystems, and the logistics for research stations near the Antarctic coast. Therefore, it is important to accurately measure the strain of fast ice and its seasonal variations, and to identify the cause of stresses on the ice. In this paper, we separate the strains from glacial stress and tidal stress of fast ice near the Campbell Glacier Tongue (CGT) in Terra Nova Bay, East Antarctica. This was done using observations from a series of one-day tandem COSMO-SkyMed Interferometric Synthetic Aperture Radar (InSAR) images obtained from December 2010 to January 2012. Firstly, we discriminated fast ice from pack ice and open water by analyzing the interferometric coherence values. We then identified the characteristics of the strains by investigating the equi-displacement lines of fringes in weekly InSAR and double-differential InSAR (DDInSAR) images. The weekly InSAR images predominantly showed glacial shear strain of the fast ice with fringes parallel to the sides of the CGT. This was due to the cumulative flow of the CGT for a week, while oscillating tidal signals were relatively small. The DDInSAR images, which cancelled glacial strain rates in two one-day InSAR images, showed a deformation of the fast ice by tidal sea surface tilt, with the fringes parallel to the coastline. Based on the unique characteristics of these strains, we separated them from the one-day InSAR images by decomposing the fringe patterns into glacial and tidal strain. Glacial shear strain rates of fast ice attached to the east of the CGT decreased from May to August owing to ice thickening and then stabilized until December. Those to the west of the CGT increased from May to July. This was possibly due to bottom melting of the ice by the increased ocean circulation during the expansion period of the nearby polynya. The glacial strain then decreased until December because of reduced polynya activity. The fast ice near the Jang Bogo Station (JBS) only showed tidal strain as it was isolated from the CGT by cracks and leads. Tidal strain rates of the fast ice were strongly correlated with the magnitude of tidal variations in all these regions, which represents shows that the tidal strain represents tidal sea surface tilt. The tidal response of fast ice to the west of the CGT and near the JBS was stronger than that to the east of the CGT, probably owing to thinner ice thickness there.

Regional changes in the flow velocity of Antarctic glaciers can affect the ice sheet mass balance and formation of surface crevasses. The velocity anomaly of a glacier can be detected using the Double-Differential Interferometric Synthetic Aperture Radar (DDInSAR) technique that removes the constant displacement in two Differential Interferometric SAR (DInSAR) images at different times and shows only the temporally variable displacement. In this study, two circular-shaped ice-velocity anomalies in Campbell Glacier, East Antarctica, were analyzed by using 13 DDInSAR images generated from COSMO-SkyMED one-day tandem DInSAR images in 2010–2011. The topography of the ice surface and ice bed were obtained from the helicopter-borne Ice Penetrating Radar (IPR) surveys in 2016–2017. Denoted as A and B, the velocity anomalies were in circular shapes with radii of ~800 m, located 14.7 km (A) and 11.3 km (B) upstream from the grounding line of the Campbell Glacier. Velocity anomalies were up to ~1 cm/day for A and ~5 cm/day for B. To investigate the cause of the two velocity anomalies, the ice surface and bed profiles derived from the IPR survey crossing the anomalies were analyzed. The two anomalies lay over a bed hill along the glacial valley where stick-slip and pressure melting can occur, resulting in temporal variation of ice velocity. The bright radar reflection and flat hydraulic head at the ice bed of A observed in the IPR-derived radargram strongly suggested the existence of basal water in a form of reservoir or film, which caused smaller friction and the reduced variation of stick-slip motion compared to B. Crevasses began to appear at B due to tensile stress at the top of the hill and the fast flow downstream. The sporadic shift of the location of anomalies suggests complex pressure melting and transportation of the basal water over the bed hill.