Okinawa Trough geophysical and topographic modeling by GDAL utilities and GRASS GIS

Polina Lemenkova

doi:10.5937/podrad2138087l

Abstract

This paper presents using GDAL utilities and GRASS GIS for topographic analysis of the raster grids based on GEBCO DEM as NetCDF file at 15 arc-second intervals. The focus study area encompasses the area around Okinawa Trough, Ryukyu trench-arc system, southern Japan, East China Sea and the Philippine Sea, West Pacific Ocean. Several GDAL utilities were applied for data processing: gdaldem, gdalwarp, gdalinfo, gdal_translate. The data were imported to GRASS GIS via r.in.gdal. Data visualization highlighted high resolution and accuracy of GEBCO grid, enabling topographic modelling at the advanced level. The algorithm of DEM processing, implemented in GDAL utility gdaldem, was used for generating multi-purpose topographic models: aspect, hillshade, roughness and topographic indices, such as Topographic Position Index (TPI), Terrain Ruggedness Index (TRI). Thematic maps (topography, geoid, marine free-air gravity) were visualized using GRASS GIS modules for raster (d.rast, r.colors, r.contour) and vector (d.vect, v.in.region, d.legend) data processing. The results demonstrated smoother bathymetry in the East China Sea and rugged relief in the Philippine Sea which corresponds to their different geological and geophysical settings. The presented methodology of the topographic analysis based on DEM demonstrated technical aspects of GDAL and GRASS as scripting approach of advanced cartography.

Highlights

This paper presents application of scripting cartographic methods for topographic data analysis and modelling by GDAL, Geospatial Data Abstraction Library (GDAL/OGR contributors, 2020) and open-source GRASS GIS (Neteler, 2001; Neteler and Mitasova, 2008)
The aim of this paper is to perform a topographic analysis of the selected study area by applying various types of topographic modelling: Topographic Index Ruggedness (TRI), Topographic Position Index (TPI), roughness, hillshade, slope orientation aspect, as well as visualizing geoid and gravimetric grids using GDAL utilities and GRASS modules (Figure 1)
Roughness of topography (Figure 6, right) shows a key geomorphometric variable widely used in geosciences (Hobson 1972; Frankel and Dolan, 2007; Grohmann et al, 2009)

Summary

Introduction

This paper presents application of scripting cartographic methods for topographic data analysis and modelling by GDAL, Geospatial Data Abstraction Library (GDAL/OGR contributors, 2020) and open-source GRASS GIS (Neteler, 2001; Neteler and Mitasova, 2008). Automated data processing in geological mapping is presented in the existing literature (Gruber et al, 2017; Maggiori et al, 2017; Krčmar et al, 2020; Bongiovanni et al, 2021; Thiele et al, 2021; Arriagada et al, 2021; Balogun et al, 2021). GRASS GIS, presented in this paper, aimed at topographic modelling for regional physical geographical analysis in the area of the Okinawa Trough and Ryukyu trencharc system. Such methodology has not been qualitatively explored in the existing papers, despite some thematic overlaps (Ohta et al, 2013; Minami and Ohara, 2020; Arai et al, 2016a; Minami et al, 2020; Li et al, 20201; Xu and Chen, 2021)

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Conclusion