Geostatistical data fusion of multiple type observations to improve land subsidence monitoring resolution in the choushui river fluvial plain, Taiwan

Abstract

Precise leveling, global positioning system (GPS), and interferometric synthetic aperture radar (InSAR) have had marked influences on the geodesy field. Many studies have applied these techniques to land subsidence monitoring and predictions. Land subsidence in the Choushui River Fluvial Plain (CRFP) in western central Taiwan is severe, primarily because of excessive groundwater pumping. Exploiting various observational techniques this study employed a geostatistical cokriging algorithm to integrate multiple types of observations for mapping land subsidence in the CRFP between 1993 and 2008 to effectively reduce the regional effects and interpolation biases in InSAR observations. Precise leveling data and persistent scatterer InSAR results were first assessed through variogram analysis, the results of which revealed similar directional variograms and no nugget effect for the experimental variograms. All observed sill values decreased with increasing temporal intervals and the ranges of the same type of observations tended to be stable for time intervals of different lengths. The accuracy of a cokriged land subsidence map was verified using continuous GPS data at the same cell locations and was significantly improved compared to when the precise leveling data were used. The cokriging interpolations of land subsidence in the CRFP indicated that the severe subsidence areas had moved from the coastal area to the central CRFP. An obvious critical subsidence migration point for the southern CRFP occurred in 1998. Overall subsidence rate trends increased in the early periods (1993 - 1998 and 1998 - 2003) and decreased in the most recent period (2005 - 2008).