Science Service System

Summary of Proposal LAN2988

TitleSubsidence-Sensitive Urbanization in developing countries: Case study of Kolkata, India
Investigator Roychowdhury, Koel - Presidency University, Department of Geography
Team Member
Dr. Bhatta, Basudeb - Jadavpur University, Department of Computer Science and Engineering
SummaryMost cities of the world are experiencing high rate of vertical expansion. Increasing building heights facilitates increase in the capacity of the urban space to accommodate more people and business. In order to provide safe drinking water to the residents, there is an increase in demand on the available ground water resources. With the advancement of technology it has become easier to extract water from much below the surface. Often due to over-extraction of sub-surface ground water many cities experience subsidence. It therefore, becomes very necessary to monitor the subsidence in order to maintain the safety of the buildings. The proposed study will look into the urban subsidence of Kolkata, the capital of the state of West Bengal, India. It is located in eastern part of the country on the eastern bank of the Hooghly River. With an urban population of 14.1 million, it is the third largest metropolitan area of India and the 8th largest urban conurbation of the world. In Kolkata city potential land subsidence caused primarily by over-drafting of groundwater, has been reported by a number of previous workers and by the local media. However, there was no correlation with the rapid urbanization and vertical growth of the city in these researches. This research aims to explore the relationship between the spatial pattern of ground subsidence due to dwindling ground water reserve and the growth of Kolkata in the vertical direction. Objectives: The main objectives of this research are: 1.To map the areas of Kolkata undergoing subsidence due to over-extraction of underground water. 2.To correlate the vertical elevation of the city with the ground subsidence. Method: A master image (reference data) and slave image (match data) will be chosen. The interferograms will be created with respect to the same master image. The master scene will be chosen such that the dispersion of the perpendicular baselines is as low as possible. In this study SRTM DEM will be used as the reference DEM. In the next step image co-registration will be carried out by semi-manual mode. Image tie points between master and the slave image will be interactively defined. The image offset resulting in the best correlation value will be locked. Well-correlated areas with less noise will be subset in the next step. In order to maximize the coherence for each of the pixels of the interferogram, a spectral shift-filtering step will be conducted. This filtering will be done in both the range and azimuth direction. A differential interferogram will be created in the next step. Phase unwrapping will be carried out in the following step to derive the absolute phase.In order to perform the height to phase conversion, the baselines will be refined. In this step, the perpendicular baseline value will be calculated using the available GCP point pairs. The step will be redone till the deviation is the smallest.The final step will include the calculation of displacement in absolute values. In this step a point will be identified with zero displacement. The phase value of this point will be subtracted from each unwrapped phase value to obtain the absolute displacement components for the output motion map images. By combining the Line-of-Sight (LOS) motion with the viewing geometry, it will be possible to compute the Horizontal and Vertical components of the LOS motion displacement. Data requirements: The following datasets will be used: 1.Three Stripmap mode (HH/VV) data collected over Kolkata on2012-10-21, 2012-11-23 and 2013-02-08. 2.Three high resolution Spotlight mode data (HH) collected on 2015-11-04(2) and 2015-05-04. Funding: The proposed research is an extension of a project sanctioned by University Grants Commission (India). The funding for the field works and infrastructure (including computer and GPS receivers) will be supported by the said project.

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