3D BATHYMETRIC MAPPING FOR NEAR SHORE USING LANDSAT-8 IMAGES; A CASE STUDY AT USWETAKEIYAWA, SRI LANKA

摘要

The bathymetric information of water features are important when initiate different activities such as sedimentation monitoring, fisheries, voyages, recreation and many reservoir base constructions. In such works, sedimentation and multi temporal environmental changes are prejudicial for consistent volume of water level. For studying such changes, 3D bathymetric map can be used as a beneficial descriptor with different bathymetries. Sounding techniques based on survey vessels are obviously time consuming, the cost of survey and the method to determine the bathymetry is based on specific equipment, which considerably limits frequent repetition. Satellite Derived Bathymetry (SDB) is a growing approach to infer bathymetry using a band ratio of satellite imagery as a supplementary approach for traditional hydrographic surveys. The calibration information by the energy attenuation due to the depth of the water column and the backscatter due to suspended loads in the water has contributed to create an image of shelf areas understandable. The study area was Uswetakeiyawa of western coastal region of Sri Lanka. First the water features were identified and the coastal region is extracted by the use of two normalized factors (NDWI and MNDWI). Coastal Aerosol and green is identified as the best band combination for bathymetric depth extraction and blue-green, Coastal Aerosol-red, blue-red combinations are also given significantly high accuracy, indicating that those ratios are also competent for extractions of near shore bathymetry based on Landsat 8. When transforming the relative bathymetry to absolute bathymetry, the accuracy is improved by different samples and obtained a high correlation of nearly 0.9 for all samples tested. The resulting depths are converted to a 3D surface map affirming the shape of the bathymetries for further analysis.