Abstract. Rock salt has remarkable mechanical properties and high economic importance; however, the strength of salt compared to other rocks makes it a rather vulnerable material. Human activities could lead to acceleration of the dissolution of soluble rock salt and collapse of subsurface caverns. Although sinkhole development can be considered a local geological disaster regarding the characteristic size of surface depressions, the deformations can result in catastrophic events. In this study we report the spatiotemporal evolution of surface deformation in the Solotvyno salt mine area in Ukraine based on Sentinel-1 interferometric synthetic aperture radar measurements. Although the mining operations were finished in 2010, several sinkholes have been opened up since then. Our results show that despite the enormous risk management efforts, the sinkholes continue to expand with a maximum line-of-sight deformation rate of 5 cm/yr. The deformation time series show a rather linear feature, and unfortunately no slowdown of the processes can be recognized based on the investigated 4.5-year-long data set. We utilized both ascending and descending satellite passes to discriminate the horizontal and vertical deformations, and our results revealed that vertical deformation is much more pronounced in the area. Analytical source modeling confirmed that the complex deformation pattern observed by Sentinel-1 radar interferometry has a direct connection to the former mining activity and is confined to the mining territory. With the 6 d repetition time of Sentinel-1 observations, the evolution of surface changes can be detected in quasi real time, which can facilitate disaster response and recovery.

Abstract. Rocksalt has remarkable mechanical properties and a high economic importance, however, this strength of salt compared to other rocks makes it a rather vulnerable material. Human activities could lead to acceleration of the dissolution of soluble rocksalt and collapse of subsurface caverns. Although sinkhole development can be considered local geological disaster regarding the characteristic size of surface depressions the deformations can result in catastrophic events. In this study we report the spatiotemporal evolution of surface deformation in Solotvyno salt mine area in Ukraine based on Sentinel-1 interferometric synthetic aperture radar measurements. Although the mining operations were finished in 2010 several sinkholes have been opened up since then. Our results show that even though the enormous risk managing efforts the sinkholes continue to expand with a maximum line-of-sight deformation rate of 5 cm/yr. The deformation time series show a rather linear feature and unfortunately no slowdown of the processes can be recognized based on the investigated 4.5 year-long data set. We utilized both ascending and descending satellite passes to discriminate the horizontal and vertical deformations and our results revealed that vertical deformation is much more dominant in the area. With the 6-day repetition time of Sentinel-1 observations the evolution of surface changes can be detected in quasi real-time which can facilitate disaster response and recovery.

<p>The impact of individual meteors on the lower ionosphere (90-150 km height) has been investigated during wintertime meteor showers using measurements of two DPS-4D Digisondes installed at Sopron (47.63°, 16.72°) and at Pruhonice (50°, 14.5°). The optical measurements of meteors have been performed by a zenith camera installed next to the digisonde at Sopron. It provided the opportunity to compare high cadence ionograms measured during meteor showers parallel with the optical data to determine the plasma trails of individual meteors. Campaign measurements with two ionograms/minute have been performed at Sopron station during the Leonid (16-18 November) and Geminid (10-15 December) meteor showers in 2019. Furthermore, skymaps (1/min) detected by the Digisonde at Sopron during the campaign were also investigated.</p> <p>In the 20-25% of the observed meteors faint, short-lived (20-120 sec) Es layers were detected on the ionograms during and after (< 2 min) the optical record, which are typical signal of individual meteor trails on the ionogram based on previous studies. There was no observed Es activity at the same height on the ionograms detected before and after these events. Furthermore, the direction of the echo can be also defined on the ionograms of the DPS-4D Digisonde thanks to the multi-beam observation technique. The direction of the detected Es layers agreed well with the optical observations in most of the cases. The maximum frequency of the observed faint layers (foEs) varied between 1,6 and 4,5 MHz, while their height was between 85 and 136 km. Points on the skymaps were also detected at the time of the faint Es layers in 40 % of the cases. The height and direction of the observed points agreed with these parameters of the plasma traces on the ionograms.</p> <p>Comparing the ionograms with the closest ionosonde observation at Pruhonice station at the same time, we could conclude that the detected faint Es layers were local plasma irregularities, no Es activity at the same height was observed there. This strengthens the hypothesis that the observed trails on the ionograms represents the echo of the optically recorded meteors.</p> <p> </p>

<p>In the last decades, the development of space geodesy methods has allowed much more accurate observations of planetary surface dynamics than before. The various SAR satellites, like global navigation systems, make their observations in different microwave frequency ranges (1-10 GHz). The Earth's atmosphere is transparent to the microwave signal, but the factors affecting wave propagation (propagation direction and velocity) in the medium are time-dependent, the medium is anisotropic, inhomogeneous and, in the case of the ionosphere, dispersive. Without the correction of such atmospheric artifacts the resulting signal delay is evaluated as a displacement during processing, which can be in the order of tens of meters.</p><p>In order to get information about the actual geophysical processes from the displacement values derived from satellite data, the effects on wave propagation must also be taken into account. Radar interferometric methods are particularly suitable for detecting processes with velocities in the order of a few mm/year, but are limited by the lack of quantitative knowledge of the signal delay in the wave propagation, which is of particular importance for the study of processes on a regional scale.</p><p>Wave propagation in the neutral atmosphere is mostly distorted by refraction due to water vapour, and the correction is complicated by the dynamic variation of the water vapour content and the inaccurate knowledge of the atmospheric water vapour. In the ionosphere, in addition to Faraday-rotation and electron density dependent refraction, the dispersive nature of the medium is another source of error.</p><p>Transient atmospheric phenomena (frontal and thunderstorm systems, ionospheric disturbances, sporadic E layers, etc.), which are predominantly inhomogeneous in nature, further complicate the correction of their effects, but also provide an excellent opportunity to study them. The Sentinel-1 satellite images cover an area  of 250 km x 250 km with  a resolution of 5 m x 20 m. This resolution may prove useful for studying atmospheric inhomogeneities.</p><p>In radar interferometric processing, virtual displacements generated by atmospheric phenomena can be investigated in areas that are assumed to be geologically stable and contain well-identified objects that provide strong signal reflection. For the latter, corner reflectors  points specifically designed for this purpose have already been developed.</p><p>In the area of Sopron (Hungary), there are 4 such installed permanent artificial reflectors. By including these points and by comparing measurements from the local ionosonde and meteorological station, we have studied the influence of atmospheric phenomena on radar interferometric processing and the applicability of radar interferometry for the study of atmospheric phenomena.</p>