Marine Science: Difference between revisions

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: http://osdir.com/ml/gis.gmt.user/2005-04/msg00087.html
: http://osdir.com/ml/gis.gmt.user/2005-04/msg00087.html


   img2grd topo_10.1b.img -T1 -S1 -V -R0/360/-80.738/80.738 -m1 -D -Gtopo_all.grd
   img2grd topo_10.1.img -T1 -S1 -V -R0/360/-80.738/80.738 -m1 -D -Gtopo_all.grd
   # (out of memory, needs 1.4gb)
   # (out of memory, needs 1.4gb)
   # try just for NZ  (W/E/S/N bounds)
   # try just for NZ  (W/E/S/N bounds)
   REGION=160/180/-50/-30
   REGION=160/180/-50/-30
   img2grd topo_10.1b.img -T1 -S1 -V -R"$REGION" -m1 -D -Gtopo_NZ.grd
   img2grd topo_10.1.img -T1 -S1 -V -R"$REGION" -m1 -D -Gtopo_NZ.grd
   grd2xyz topo_NZ.grd -S > topo_NZ.xyz
   grd2xyz topo_NZ.grd -S > topo_NZ.xyz
   
   

Revision as of 05:49, 18 September 2008

this page is a work in progress

Tools for marine scientists

Bathymetry processing

Please expand


Bathymetric data

ETOPO2v2 data download
  • Smith and Sandwell 1-minute global elevation v10.1, May 13, 2008
http://topex.ucsd.edu/marine_topo/mar_topo.html (712mb)

global_topo_1min/README_V10.1.txt file:

Version 9.1 has a very different FORMAT than V8.2
The main differences are that the grid spacing in 
longitude is now 1 minute rather than 2 minutes.
In addition, the latitude range is increased to 
+/- 80.738.  Like the old versions, the elevation(+)
and depth(-) are stored as 2-byte integers to the nearest meter.
An odd depth of say -2001m signifies that this pixel was constrained
by a real depth sounding while an even depth of say -2000m is
a predicted depth.

Here are the parameters for the old and new versions:
param    V8.2     V9.2
___________________________
nlon     10800    21600
nlat     12672    17280
rlt0   -72.006  -80.738
rltf    72.006   80.738
___________________________

The binary format of the integers is bigendian so the bytes need to be 
swapped if you are running on an Intel processor.
Here is a typical command for swapping bytes:
dd if=topo_9.1.img of=topo_9.1.img.swab bs=21600 conv=swab.
  • GMT's img2grd + grd2xyz shows FP elevation values to the nearest cm not meter. Are these from contributed datasets? How does that fit with the odd/even real/interpolated soundings?


Import using GMT

Process with GMT's img2grd to convert from spherical Mercator projection to geographic coordinates, then import into GRASS

http://osdir.com/ml/gis.gmt.user/2005-04/msg00087.html
 img2grd topo_10.1.img -T1 -S1 -V -R0/360/-80.738/80.738 -m1 -D -Gtopo_all.grd
 # (out of memory, needs 1.4gb)
 # try just for NZ   (W/E/S/N bounds)
 REGION=160/180/-50/-30
 img2grd topo_10.1.img -T1 -S1 -V -R"$REGION" -m1 -D -Gtopo_NZ.grd
 grd2xyz topo_NZ.grd -S > topo_NZ.xyz

 # get adjusted region bounds and resolution from img2grd output
 # ** check that rows and columns match **
 g.region n=-29.9945810754 s=-50.0056468984 w=160E e=180 \
    ewres=0:01 nsres=0.0126094 -p

 r.in.xyz in=topo_NZ.xyz out=topo_NZ_1min fs=tab
 r.colors output=topo_NZ_1min color=etopo2

To save a step or some disk space, in the above you could set the region first then pipe grd2xyz directly into r.in.xyz instead of creating the .xyz file.

 # create a r.in.xyz "n" map to test input point coverage
 r.in.xyz in=topo_NZ.xyz out=topo_NZ_1min_n fs=tab method=n
 # check rast map stats, min=max=1 and there should be no null cells
 r.univar topo_NZ_1min_n
 # cleanup
 g.remove topo_NZ_1min_n

or, import GMT .grd file directly (old GMT grd format introduces FP +0.005 elev shift error??). New GMT netCDF format .grd files can be imported with the r.in.gdal module.

 # convert COARDS-compliant netCDF grdfile to old GMT native .grd
 grdreformat topo_NZ.grd topo_NZ_old.grd=bf
 # import
 r.in.bin -hf in=topo_NZ_old.grd out=topo_NZ_old
Import directly

To load it into GRASS lat/lon location (spherical):

Location setup:
http://thread.gmane.org/gmane.comp.gis.gmt.user/918
http://article.gmane.org/gmane.comp.gis.proj-4.devel/192/

Is it even possible to load directly into GRASS?

Set up Mercator/Sphere location:

  • g.setproj commands for manual projection settings
Projection type> D "other"
proj> merc
No datum
ellipsoid> sphere
radius> default (doesn't matter)
Scale Factor> 1.0
Latitude of True Scale> 0
Central Meridian> 0

Which creates:

G63> g.proj -j
+proj=merc
+k_0=1.0000000000
+lat_ts=0.0000000000
+lon_0=0.0000000000
+a=6370997
+b=6370997
+no_defs
+to_meter=1.0

G63> g.proj -w
PROJCS["Mercator",
   GEOGCS["unnamed",
       DATUM["unknown",
           SPHEROID["unnamed",6370997,"inf"]],
       PRIMEM["Greenwich",0],
       UNIT["degree",0.0174532925199433]],
   PROJECTION["Mercator_2SP"],
   PARAMETER["standard_parallel_1",0],
   PARAMETER["latitude_of_origin",0],
   PARAMETER["central_meridian",0],
   PARAMETER["false_easting",0],
   PARAMETER["false_northing",0],
   UNIT["meter",1]]


MRWORLD:PROJCS["unnamed",PROJECTION["Mercator_1SP"],
 PARAMETER["latitude_of_origin",0],
 PARAMETER["central_meridian",0],
 PARAMETER["scale_factor",1],
 PARAMETER["false_easting",20000000],
 PARAMETER["false_northing",0]]

Note Mercator_1SP vs. Mercator_2SP in the above. (does 2 std parallels merc with only one defined == 1 std par merc?)


  • Load using r.in.bin
 # the following does not work correctly, just a trial
 # offset n,s,e,w by 1/2 a grid cell?
 r.in.bin input=topo_9.1b.img output=topo_9.1b \
      title="1' worldwide relief (1.852 km-sq)" \
      -b -s bytes=2 rows=17280 cols=21600 \
      n=80.738 s=-80.738 w=0 e=360

  r.colors output=topo_9.1b color=etopo2
Official coloring

Download the "official" GMT color rules from:

wget ftp://topex.ucsd.edu/pub/global_topo_1min/gmt_examples/map/topo.cpt

Convert HSV GMT cpt color rules to RGB GRASS color rules with the r.cpt2grass add-on script.

r.cpt2grass in=topo.cpt out=palette_topo.gcolors

(HSV -> RGB conversion in that script is now partially functional)

Multibeam sonar processing

MB-System

  • MB-System is Free software for the processing and display of swath sonar data. It can handle both multibeam bathymetry and sidescan sonar image data.
Import into GRASS
See also the GRASS and GMT wiki help page.


  • Ungridded data points may be piped directly from mblist to GRASS's v.in.ascii module. See the v.colors addon script for colorizing point data in GRASS (v.colors may be unsuitable for massive datasets).

Examples:

1) Export Lat/Lon + depth data from XTF datafile into a GRASS Lat/Lon location

mblist -I 074.XTF -OXYz | v.in.ascii out=track074 x=1 y=2 fs=tab

2) Export Lat/Lon from the XTF datafile, reproject into the current GRASS location's projection, and import into GRASS with v.in.ascii

mblist -I 074.XTF -OXY | m.proj -i | cut -f1 -d' ' | \
  v.in.ascii out=track074 x=1 y=2 fs=tab

Idea: write a v.in.cdl script that will parse a NetCDF/CDL file and automatically set v.in.ascii's column= option with column names and types.

Sidescan sonar processing

  • i.warp script for georectifying and mosaicking scanned paper rolls into a GeoTIFF with GDAL's gdalwarp program

Wave exposure

  • Using GRASS to prepare and process data for the SWAN Wave Model

Circulation models

  • Preparing input grids
    • r.in.mat and r.out.mat

Tutorials

Remote Sensing

  • Importing MODIS Aqua SST and chlorophyll-a data, SeaWiFS chlorophyll-a, and Pathfinder AVHRR SST satellite images.

Mapping and Cartography