Bathymetry is the science of determining the topography of the seafloor. Bathymetry data is used to generate navigational charts, seafloor profile, biological oceanography, beach erosion, sea level rise, etc. A number of methods are available for determining ocean bathymetry, using either active sensor such as sonar, lidar or passive multispectral imagery such as Ikonos, WorldView and Landsat. Determining the bathymetry using sonar and LiDAR is very expensive, while Ikonos and Worldview are commercially available multispectral satellite platforms whereas Landsat satellite imagery provides a free and publicly available data. Therefore, the present study makes an attempt to determine the bathymetry mapping of the southwest coast of India (13° 0' 0" N and 74°50' 0" E) by applying the ratio transform algorithm on the blue and green bands of Landsat 8 satellite imagery. The statistical indices such as R2, RMSE and MAE are computed between the algorithm derived value and the hydrographic chart sounding value. The result shows a good correlation between the algorithm derived value and hydrographic chart sounding value. © 2015 The Authors. Published by Elsevier Ltd.