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Estimation of Land Subsidence Using Sentinel Image Analysis and Its Relation to Subsurface Lithology Based on Resistivity Data in the Coastal Area of Semarang City, Indonesia

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Widada S. , Zainuri M. , Yulianto G. , Satriadi A. , Wijaya Y. J.

2020

tom Vol. 21, nr 8

47--56

The Semarang city is the capital of the Central Java Province that is experiencing rapid urban growth. Land subsidence in Semarang has been widely reported and its impacts can be seen already in daily life. In order to minimize its damage, land subsidence monitoring is required as a part of natural disaster mitigation. On the other hand, understanding of the subsurface lithology conditions is needed to explore the causes of subsidence in certain areas. One of the methods of monitoring land subsidence is by utilizing Synthetic Aperture Radar (SAR) satellite image which is used in this research. In turn, the subsurface lithology can be studied with the geoelectric methods, one of which is the resistivity method. The purpose of this research is to estimate the land subsidence in the Semarang city using the Sentinel Image Analysis by means of the DInSAR Method and its relation with subsurface lithology studied using the resistivity geoelectric method. The result of the research shows that the average value of subsidence was located in the Genuk District area and Semarang Utara District area which each subsidence value is 9.8 cm/year and 12.7 cm/year. This is because the lithology under the surface of the two locations is clay and silt in a soft condition that is thicker than other locations. The saltwater content contributes to the consolidation process in the lithology. There is a tendency that land subsidence is greater in the port and industrial areas than in other regions, due to building loads.

The Temporal Trends in Chlorophyll-A Concentration along the Southern Coast of Papua over a 25-year Period, from 1998 to 2022

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Wijaya Y. J. , Munandar B. , Wisha U. J. , Hidayat E. F. , Rejeki H. A. , Ismunarti D. H.

tom Vol. 24, iss. 6

82--93

The region situated along the southern coast of Papua Island exhibits a considerable likelihood of upwelling, which is distinguished by higher amounts of chlorophyll-a concentration. The present study examined the variability of upwelling phenomena spanning a period of 25 years (1998-2022) through the utilization of satellite-derived data obtained from the Ocean-Colour Climate Change Initiative (OC-CCI). Apart from the chlorophyll-a concentration, the southern region of Papua exhibits a significant amount of suspended sediment contamination, as indicated by the observations of Rrs 555. Upon conducting EOF analysis during each season, it has been observed that there has been a significant rise in the levels of chlorophyll-a concentrations over the past several years in the northern region of the Arafura Sea. The period spanning from 2016 to 2022 witnessed a rise in precipitation amounts, leading to a greater transportation of nutrients through water discharge and consequently resulting in an increase of chlorophyll-a concentration.