Potential use of spectral analysis to delineate coastal boundary of a landmass based on estimation soil salinity and salt water intrusion: a preliminary result

摘要

Determining coastal boundaries on land is essential to understanding the process of soil salinization. Once, It can be observed, and the coastal boundaries may help explain these areas' damage levels. This study aimed to observe the change in soil salinity and saltwater intrusion and use both values to determine the coastal boundaries in Subang, Indramayu, and Cirebon regencies. This study employed a multi-temporal data of Landsat 5 TM and Landsat 8 OLI-TIRS satellite imageries (2009-2015), the water spectral reflectance collected from the field survey, and the elevation data to gain the elevation information. The corrected Landsat and water reflectance data were combined and processed to obtain the saltwater intrusion using soil salinity index (SSI), salinity index (SI), brightness index (BI), normalized difference salinity index (NDSI), soil salinity index (S SI), and water salinity index (WSI). Besides that, five linear and multiple regression equations as a semi-empirical model, namely saltwater intrusion index (SWII), are also used. Only BI, SSI, and two SWII models show reasonable saltwater intrusion with 44%, 24%, and 52% accuracy. These models with below 0.2 (dS/m) represented the non-saline, while others used the saline regime to determine the boundaries. The spatial distribution of saltwater intrusion may become unreliable since its accuracy does not always relate to the land cover. Since the acceptable models mostly elucidate that the entire region in Indramayu regency has been experiencing saltwater intrusion since 2015, the boundaries are far from the coastline.