GPS is frequently used in the monitoring of natural hazards and other geophysical phenomena. Landslide monitoring is one such area in which various GPS methods are tested and various systematic error sources are introduced. In previous studies, one error source introduced on rapid static GPS was the effect of large height differences in GPS positions. In this study, we further investigate how GPS velocities/slip rates are affected by large station height differences when rapid static surveying is used. In order to demonstrate the influences, we used static GPS measurements from the Koyulhisar landslide in central Turkey. Comparison of rapid static GPS solutions with static GPS solutions using BERNESE 5.0 indicates that systematic biases occur in the estimated rapid static GPS deformation rates when the station height difference is large between baseline points. The effect is more significant on the vertical component, whereas it is negligible on the horizontal components. When reducing the height difference between the reference station and the rover stations, rapid static solutions from 15-min sessions show high correlation and similar deformation rates with static positioning solutions.
There are numerous methods used nowadays to monitor landslide movements. Of these methods, Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) are the ones that are most commonly used. In this study, the amounts of movements acquired via these two methods were compared and relations between them were analysed. The Koyulhisar landslide region was selected as the field of study. In this study, 10 Envisat images of the region taken between 2006 and 2008 were evaluated using Persistent Scatterers Interferometric Synthetic Aperture Radar (PSInSAR) technique and annual velocity values at the direction of line of slight at PS points were obtained for the region of interest. The velocity values were then obtained from PSInSAR results and compared with those obtained from six periods of GNSS measurements that were performed between April 2007 and November 2008 on Koyulhisar Landslide area after which the relationship between the two was analysed. Two different movement models from GNSS and PSInSAR results were fit to the landslide region. The velocity values estimated from these movement models for the region were compared and correlation between them was determined. As a conclusion, a high correlation of r D 0.84 was determined between the models obtained from nine GNSS points, except one point at the city centre, and PSInSAR.
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