Malte Vöge

Potential of SAR intensity tracking technique to estimate displacement rate in a landslide-prone area in Haridwar region, India

Landslides constitute one of the major natural hazards that could cause significant loss of life and various human settlements. Mansa Devi hill near Haridwar city has encountered with such potential hazard for several years due to the instability of the slopes. Therefore, preparedness both on regional and site-specific basis at spatial level in the form of surface movements is extremely important to diminish the damage of human life and settlements. Though the surface movement measurement through field-based technique is always very accurate, this technique is time-consuming and unfeasible over a widely affected region. Therefore, areal and satellite remote sensing is gaining importance in landslide investigation due to its wide coverage. In recent years, synthetic aperture radar has already proven its potential for mapping ground deformation due to earthquake, landslide, volcano, etc. Therefore, in this study, an attempt has been made to identify the potential landslide-affected region in Mansa Devi area using one multi-temporal SAR technique and intensity tracking technique. Intensity tracking technique has identified significant mass movement in the landslide-affected region where the other conventional multi-temporal technique, SBAS, fails. An error analysis has been carried out in order to demonstrate the applicability of intensity tracking technique. This study demonstrated that intensity tracking can be considered as an alternative to conventional interferometry for the estimation of land surface displacement when latter is limited by loss of coherence due to rapid and incoherent surface movement and/or large acquisition time intervals between the two SAR images.

Surface displacement estimation using multi-temporal SAR Interferometry in a seismically active region of the Himalaya

The Indian subcontinent is one of the most earthquake-prone regions of the world. The Himalayas are well known for high seismic activity, and the ongoing northwards drift of the Indian plate makes the Himalaya geodynamically active. During the last three decades, several major earthquakes occurred at the plate interiors and boundaries in this subcontinent causing massive losses. Therefore, one of the major challenges in seismology has been to estimate long recurrence period of large earthquakes where most of the classical Probabilistic Seismic Hazard Approaches fail due to short catalogues used in the prediction models. Therefore, during the past few decades, the Himalayan region has been studied extensively in terms of the present ongoing displacements. In this context the present study has been carried out to estimate the surface displacement in a seismically active region of the Himalaya, in between Ganga and Yamuna Tear, using multi-temporal Synthetic Aperture Radar (SAR) Interferometry. A displacement rate of 6.2–8.2 mm/yr in N14°E direction of the Indian plate towards the Tibetan plate has been obtained. It has been noted that the estimated convergence rate using Differential SAR Interferometry technique is relatively low in comparison with those obtained from previous classical studies. The reported low convergence rate may be due to the occurrence of silent/quite earthquakes, aseismic slip, differential movement of Delhi Hardwar ridge, etc. Therefore, in view of the contemporary seismicity and conspicuous displacements, a study of long-term observations of this surface movement has been recommended in future through a time-series SAR Interferometry analysis.

From Manual to Automatic AEM Bedrock Mapping

ABSTRACT An extensive airborne electromagnetic (AEM) survey was carried out in Norway with the primary purpose to obtain information of depth to bedrock in areas with little or no prior geotechnical knowledge. We present different approaches to extract a bedrock model from the high-resolution time-domain AEM data, including both automated and manual procedures. It was found that in the area of investigation a user-driven approach of manual bedrock picking was the most suitable, taking into account the strongest vertical resistivity gradient and geological information as additional information. A semi-automatic, statistical method, called Localized Smart Interpretation (LSI), is also presented and discussed. This method, while not included in the original bedrock model for the entire area, showed promising results while using less time compared to the fully manual approach. It is recommended that LSI be considered in future projects of similar scope.

Efficient 2D Hybrid Inversion of Airborne Frequency Domain Data

We present a 2D inversion code for frequency-domain HEM data designed for inverting field scale surveys on normal desktop computers. The fundamental algorithm is a 2.5D algorithm with field separation into primary and secondary fields. Due to limited memory, as well as performance concerns, sectioning is introduced for splitting large surveys into smaller sections. Sectioning is only done when calculating the 2D forward and derivatives, and it is done with a sufficient overlap, such that vital 2D information is preserved. The algorithm uses a hybrid scheme which i) starts with 1D forward and inverse calculations, ii) then switches to 2D forward calculations and 1D derivatives, and iii) finally ends with full 2D calculations. The result of this is a code which produces results like a 2D code, but with a substantially shorter computational time.