Using regional Global Positioning System (GPS) networks, we studied three‐dimensional spatial structure of ionospheric total electron content (TEC) anomalies preceding three recent large earthquakes in Chile, South America, i.e., the 2010 Maule (M_w 8.8), the 2014 Iquique (M_w 8.2), and the 2015 Illapel (M_w 8.3) earthquakes. Both positive and negative TEC anomalies, with areal extent dependent on the earthquake magnitudes, appeared simultaneously 20–40 min before the earthquakes. For the two midlatitude earthquakes (2010 Maule and 2015 Illapel), positive anomalies occurred to the north of the epicenters at altitudes 150–250 km. The negative anomalies occurred farther to the north at higher altitudes 200–500 km. This lets the epicenter, the positive and negative anomalies align parallel with the local geomagnetic field, which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges.

Using ionospheric total electron contents residual data from 146 Global Navigation Satellite System stations in South America, we conducted three‐dimensional tomography of ionospheric electron density anomalies immediately before the 2015 Illapel M _w 8.3 earthquake, Central Chile. We used five GPS and five GLONASS satellites and applied continuity constraints to regularize the linear least squares inversion. The reconstructed anomalies are composed of positive and negative regions, at altitudes of ~200 km and ~400 km, respectively, distributed roughly along the geomagnetic field. This feature suggests that the observed anomalies occurred by the downward E  ×  B drift of electrons due to electric fields within ionosphere, possibly caused by surface positive electric charges. We also discuss the existence of the mirror image anomalies near the geomagnetic conjugate point of the epicenter using stations in Colombia.

Mapping deformation field time-series, including vertical and horizontal motions, is vital for landslide monitoring and slope safety assessment. However, the conventional differential synthetic aperture radar interferometry (DInSAR) technique can only detect the displacement component in the satellite-to-ground direction, i.e., line-of-sight (LOS) direction displacement. To overcome this constraint, a new method was developed to obtain the displacement field time series of a slope by coupling DInSAR based small baseline subset approach (DInSAR-SBAS) with multiple-aperture InSAR (MAI) based small baseline subset approach (MAI-SBAS). This novel method has been applied to a set of 11 observations from the phased array type L-band synthetic aperture radar (PALSAR) sensor onboard the advanced land observing satellite (ALOS), spanning from 2007 to 2011, of two large-scale north–south slopes of the largest Asian open-pit mine in the Northeast of China. The retrieved displacement time series showed that the proposed method can detect and measure the large displacements that occurred along the north–south direction, and the gradually changing two-dimensional displacement fields. Moreover, we verified this new method by comparing the displacement results to global positioning system (GPS) measurements.

We report the three‐dimensional (3D) structure of the electron depletion caused by the great Solar eclipse on 21 August 2017 derived from dense GNSS TEC observations. A linear least‐squares inversion was performed with a continuity constraint to stabilize the solution. The reconstructed 3D ionospheric electron density depletion showed a peak height at ~200km. The depletion reached 42%, 60%, and 72%, below 250 km, 350 km, and 450 km, respectively, and the vertically integrated (150‐450 km) decrease was 54%. We validated the accuracy of the electron density depletion at 200 km above the Millstone Hill observatory with the incoherent scatter radar (ISR) observation, and at 400 km using the in‐situ measurement by the Swarm satellite. The coincidence suggests that 3D tomography is useful for investigating the vertical structure of eclipse‐induced ionospheric changes. We further detected the electron depletion and enhancement with maximum values of 1.4‐1.9 TECU and 0.7‐1.0 TECU, respectively, in the geomagnetic conjugate region in the southern hemsisphere.