Bathymetric grids, with high resolution multibeam where available, and radar
altimetry/single beam where nothing better exists.
- Connect to
http://www.marine-geo.org/tools/maps_grids.php
- Use the small black square icon on the top center to graphically select
a region.
- If you want to merge regions, type in coordinates. At the highest
resolution (stated as about 61 m, but actually in arc seconds), you can get
grids over 150 MB in size.
- Click on the mask below Base layers in the upper right to see the ship
tracks and where there will be high resolution bathymtery. The grids
include land, but typically have a gap in shallow water where
mulitbeams can only collect very narrow swaths.
- Pick if you want
masked or unmasked data.
- Pick geotiff format.
- Pick maximum grid resolution. If the resolution in the
upper right does not match what you picked, your region is too large, and
you should select a smaller region. You should be able to get a grid
size of about 61 m.
- You can Open and merge DEMs, so if you
cannot get all of your region at 61 m resolution, you can break it into
smaller segments for the download, and then merge them.
- If you have a really large region, you can get a lower resolution
for the entire area (or just use
ETOPO1 ,
and then get the 61 m resolution for interesting areas.
- Of course the 61 m resolution only makes sense if the area has good
multibeam bathymetery.
- Format
- The ArcASCII version is larger (twice the size of the Geotiff)and
loads more slowly, but works correctly as of 5/4/2021. Do a Save DEM
as and pick the MD format after it loads.
- Other formats will be much harder to use. The GMT v3 Compatible NetCDF works if you have
GDAL installed. You might have to multiply
the values by -1.
- The Geotiff export made multiple changes
during spring 2019 and both MICRODEM and QGIS had problems. This
appeared to be fixed. As of 5/4/2021, the Geotiffs have no
registration information, just the corner coordinates but no indication
of the projection.
OpenTopography also has GMRT, with limited
registration information.
Open Grid/DEM to view the map.
Reference:
- Ryan, W.B.F., S.M. Carbotte, J.O. Coplan, S. O'Hara, A. Melkonian, R.
Arko, R.A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, J. Bonczkowski,
and R. Zemsky (2009), Global Multi-Resolution Topography synthesis, Geochem.
Geophys. Geosyst., 10, Q03014, doi:
10.1029/2008GC002332
Last revision 4/6/2021