Liming He

Mapping Two-Dimensional Deformation Field Time-Series of Large Slope by Coupling DInSAR-SBAS with MAI-SBAS

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.

Three-dimensional distribution of ionospheric anomalies prior to three large earthquakes in Chile

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 (Mw8.8), the 2014 Iquique (Mw8.2), and the 2015 Illapel (Mw8.3) earthquakes. Both positive and negative TEC anomalies, with areal extent dependent on the earthquake magnitudes, appeared simultaneously 20-40 minutes before the earthquakes. For the two mid-latitude earthquakes (2010 Maule and 2015 Illapel), positive anomalies occurred to the north of the epicenters at altitudes 150-250 km. The negative anomalies occurred further 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.

Seismo-ionospheric anomalies detection based on integrated wavelet

In this paper, we proposed a wavelet-based methodology that enables to detect and diagnose the ionospheric anomalies associated with seismic activity. Wavelet transform and cross-wavelet analysis methods are used to detect and identify the spatio-temporal variability of ionospheric perturbation associated with Wenchuan Ms8.0 earthquake, 12 May 2008 in China, and to gain further insights into the dynamical relations between the ionospheric anomaly variability and the geophysical indices variability in the same span of observations, 12 April ∼ 12 May, 2008. The details of the algorithm and the analysis results are introduced in this paper.

Three‐Dimensional Tomography of Ionospheric Anomalies Immediately Before the 2015 Illapel Earthquake, Central Chile

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 Mw8.3 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.

Representation on the variation of earth system phenomenon based on SDOG-ESSG: Ionosphere as an example

Representation on the variation of Earth system phenomenon is important to Earth System Science research. However, owing to the complexity and unnecessary transformation, mathematic models are not good method to represent the variations of earth system phenomena. Grid-based models can overcome the shortcomings well. But the grid in used is not perfect enough. A three-dimensional (3D) Global Spatial Grid (GSG), named SDOG-ESSG, was adopted to represent the 3D and large-scale earth system phenomena. The models of variation representation was proposed, and the experiment on ionosphere was taken to prove the superiority of the methods.

Short timescale variations in ionosphere caused by irregular solar electromagnetic radiation

Solar activity dependency of the ionosphere in local region during a short timescale is of great importance for the analysis of ionospheric anomalies probably caused by local events such as earthquakes and volcanic eruptions. Recently, a nonlinear background removal method based on multiresolution wavelet transform (MWT) for seismo-ionospheric anomaly analysis has been developed by He et al. To further evaluate the method performance, three years of different solar activity levels have been chosen to examine the relationship between the TEC variations and solar activities during 23rd solar cycle. The results showed that the MWT-based method is able to handle well the solar radiation background in the ionospheric TEC data, especially under a complex solar activity situation.