satbath (Mapping Toolbox)

Read predicted global 2-minute (4 km) topography from satellite bathymetry

Syntax

[latgrat,longrat,map] = satbath
[latgrat,longrat,map] = satbath(scalefactor)
[latgrat,longrat,map] = satbath(scalefactor,latlim,lonlim)
[latgrat,longrat,map] = satbath(scalefactor,latlim,lonlim,gsize)

Background

This is a global bathymetric model derived from ship soundings and satellite altimetry by W.H.F. Smith and D. T. Sandwell. The model was developed by iteratively adjusting gravity anomaly data from Geosat and ERS-1 against historical track line soundings. This technique takes advantage of the fact that gravity mirrors the large variations in the ocean floor as small variations in the height of the oceans surface. The computational procedure uses the ship track line data to calibrate the scaling between the observed surface undulations and the inferred bathymetry. Land elevations are reduced resolution versions of GTOPO30 data.

Description

[latgrat,longrat,map] = satbath reads the global topography file for the entire world, returning every 50th point. The result is returned as a general matrix map.

[latgrat,longrat,map] = satbath(scalefactor) returns the data for the entire world, subsampled by the integer scalefactor. A scalefactor of 10 returns every 10th point. The matrix at full resolution has 6336 by 10800 points.

[latgrat,longrat,map] = satbath(scalefactor,latlim,lonlim) returns data for the specified region. The returned data will extend slightly beyond the requested area. If omitted, the entire area covered by the data file is returned. The limits are two-element vectors in units of degrees, with latlim in the range [-90 90] and lonlim in the range [-180 180].

[latgrat,longrat,map] = satbath(scalefactor,latlim,lonlim,gsize) controls the size of the graticule matrices. gsize is a two-element vector containing the number of rows and columns desired. If omitted, a graticule the size of the map is returned.

Remarks

Land elevations are given in meters above mean sea level. The data is stored in a Mercator projection grid. As a result, spatial resolution varies with latitude. The grid spacing is 2 minutes (about 4 kilometers) at the equator.

This data is available over the Internet, but subject to copyright. The data file is binary, and should be transferred with no line-ending conversion or byte-swapping. This function carries out any byte-swapping that may be required. The data requires about 133 Megabytes uncompressed.

The data is available over the Internet via anonymous FTP from

<ftp://topex.ucsd.edu/pub/global_topo_2min/>.

Download the latest version of file topo_x.2.img, where x is the version number, and rename it topo_6.w.img for compatibility with the satbath function.

Some documentation is also available over the World-Wide-Web from

 <http://topex.ucsd.edu/marine_topo/mar_topo.html>

and

 <http://www.ngdc.noaa.gov/mgg/announcements/
announce_predict.html>.

Examples

Read the data for the Falklands Islands (Islas Malvinas) at full resolution.

[latgrat,longrat,mat] = satbath(1,[-55 -50],[-65 -55]);
whos
  Name          Size         Bytes  Class

  latgrat     247x301       594776  double array
  longrat     247x301       594776  double array
  mat         247x301       594776  double array

See Also

tbase
TerrainBase Global 5-Min digital terrain data extraction

gtopo30
30-Arc-Sec global digital elevation data extraction

egm96geoid
15-minute gridded geoid heights from the EGM96 geoid model of the Earth

`tbase`	TerrainBase Global 5-Min digital terrain data extraction
`gtopo30`	30-Arc-Sec global digital elevation data extraction
`egm96geoid`	15-minute gridded geoid heights from the EGM96 geoid model of the Earth

readfk5 tbase