GRASS GIS MODULES FOR TOPOGRAPHIC AND GEOPHYSICAL ANALYSIS OF THE ETOPO1 DEM AND
RASTER DATA: NORTH FIJI BASIN, PACIFIC OCEAN
Polina Lemenkova1
1 Schmidt Institute of Physics of the Earth, Russian Academy of
Sciences. Laboratory of Regional Geophysics and Natural Disasters (Nr. 303).
Bolshaya Gruzinskaya St, 10, Bld. 1, Moscow, 123995, Russian Federation. ORCID
ID: 0000-0002-5759-1089. Email:
pauline.lemenkova@gmail.com.
Abstract: - GRASS GIS Modules for Topographic and Geophysical Analysis of
the ETOPO1 DEM and Raster Data: North Fiji Basin, Pacific Ocean The paper
presents topographic analysis based on the raster data (NetCDF and grid formats)
and visualization of the geophysical datasets that resembles the topographic
surface. Geographically, the research focuses on the region of North Fiji Basin,
South Pacific Ocean. North Fiji Basin is one of the marginal basins located at
the converging boundary between the Pacific and Australian tectonic plates and
is notable for complex geological settings. Methodology is based on GRASS GIS
and includes scripting and cartographic visualization. Data include ETOPO1,
GEBCO, EGM96 gravity and geoid raster grids imported to GRASS GIS via GDAL
library (‘r.in.gdal’ module) from NetCDF and GRD formats, evaluated and
visualized. Several GRASS modules were used as a sequential scripting for
displaying and modelling data. Geomorphometric analysis (slopes, curvature,
aspect, elevation) was performed by module ‘r.slope.aspect’ based on ETOPO1
grid. Statistical data analysis (histograms, polar diagram) for topographic and
geoid gravitational fields were visualized by combination of GRASS modules
d.rast, g.region, d.polar, d.histogram, d.grid, d.legend, d.text. Topographic
analysis reveal that free-air gravity anomaly mark the continental shelf-slope
border showing that generally, geophysical settings are dominated by the
topographic effect. These observations are consistent with the inferred
prominent role of the geophysical settings. The histograms reveal that
topography (trenches, abyssal plains, shelf areas) has values between -5,000 and
-1,000 m, and a clear peak with major values between 100 and 350 m above sea
level. This distribution indicates that dominating depths of the ocean floor in
North Fiji Basin are between -1,500 to -3,000 m. The aspect map of the ETOPO1
initial raw raster grid show that the surface has mostly 50°-110° oriented slope
followed by data range in 250°-300° oriented slopes which is well correlating
with submarine topography and general relief forms. The steepening of the
gravity values between 50 and 55 mGal and 58 to 63 mGal indicates geoid
undulations suggesting that bathymetry is controlled by the geological settings
in the study area. Consolebased scripts of GRASS GIS are presented together with
cartographic outputs showing its effectiveness for the geographic spatial
analysis.
Keywords: GRASS GIS, transect, profile, topography, Fiji, Pacific Ocean,
bathymetry
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