MONITORING OF LAND SUBSIDENCE IN NORTHERN INDIA USING TIME-SERIES INSAR TECHNIQUE

Abstract

The population is increasing rapidly in many of the major older cities, and disorganized urban expansion in many countries is introducing adverse impacts on the environment such as contamination of shallow aquifers, soil erosion, and fall in groundwater(GW) levels as well as deformation including land subsidence. Land subsidence is already being scene in many of the big cities like Mexico, Jakarta etc. As India is largest user of GW, Land subsidence is a serious threat to cities in India. This study is made to present the upcoming land subsidence threats with the help of interferometry. Monitoring subsidence by conventional methods requires precise field measurements and is time consuming. In this study Persistent Scatterer InSAR (PS-InSAR) technique is used to monitor the subsidence using Sentinel -1 Interferometric wide swath (IW) mode. The Persistent Scatterer (PS) points are the stable targets which do not decorrelate much over time. The deformation calculated for all the PS points and a time series, and hence velocity maps are formed. For confidence in subsidence results the same technique is applied first in Delhi and results are compared with previous studies available. In Delhi this study found the subsidence in Kapashera, Dwarka near IGI airport to have a steep trend as also suggested by previous studies. Kapashera and Dwarka area is seen to have a steady rate of 2.5 cm/yr subsidence in line of sight direction and 1.5 cm/yr uplift in the line of sight direction respectively. As the Kapashera area is seen to have a maximum subsidence of more than 11 cm/yr in LOS direction, areas near Kapashera like Bijwasan and Dundahera are also subsiding at a maximum rate of 3.2 cm/yr and 3.42 cm/yr respectively away from the line of sight direction. As suggested by previous studies these deformations are in accordance of the groundwater depletion. After this PS InSAR is applied in two areas of Punjab where groundwater is seen to depleting rapidly namely Sangrur and Ludhiana. In Punjab after adopting the rice-wheat cropping system water demand for irrigation purposes has increased a lot. This study found a maximum vertical subsidence of 10mm/yr in Focal point Ludhiana. This study demonstrates the trends of deformation are not very steep at the moment but are in accordance with the groundwater table trend.