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README.EUMETSAT
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README.EUMETSAT
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Using EUMETSAT grib2 fields
Some of the EUMETSAT data is on a space view perspective grid.
-sh-3.00$ wgrib2 LMPEF_CLM_110328_0945.grib2 -grid
1:0:grid_template=90:winds(N/S):
Space view perspective or orographic grid (3712 x 3712) units 1e-06
input EW:SN output WE:SN res 0
sub-sat point: lat 0.000000 lon 0.000000 ix=1856.000000 iy=1856.000000
diameter of earth dx=3622 dy=3610 grid cells ori_angle 0.000000
sat. altitude=6.610700 (equatorial radii) grid_origin Xo=0 Yo=0
wgrib2 v1.9.3 adds support for space view perspective grids with the restriction
that orientation angle (ori_angle) is 0 and sub-sat point has a latitude of 0.
The rest of the text assumes that you have a space view perspective file.
Displaying with GrADS
My version of GrADS is not using the latest g2clib can couldn't handle product
definition template 4.30. So here is what I did.
* make a copy of the grib file product with def template 4.0
wgrib2 LMPEF_CLM_110328_0945.grib2 -set_pdt 0 -set_var CLOUDM -grib new.grb
1:0:d=2011032809:CLOUDM:no_level:-1 missing fcst:
* make a control file
g2ctl -raw new.grb >new.ctl
* make a index file
gribmap -i new.ctl
Note that my grib file only had one field. Some EUMETSAT grib files have
mutiple fields on different grids. g2ctl will get confused files that have
more than one grid. Your grib file must only have one grid.
When you run GrADS on your file, you will see the raw satellite data.
Getting grid point information
To get the value of the grid point nearest to a specified lat-lon.
-sh-3.00$ wgrib2 new.grb -lon 10 30
experimental space_view2ll scan=12
experimental space_view2ij
1:0:lon=10.009994,lat=30.005756,val=1
To get the value of a grid point
-sh-3.00$ wgrib2 new.grb -ijlat 1 1
experimental space_view2ll scan=12
1:0:(1,1),lon=999.000000,lat=999.000000,val=3
-sh-3.00$ wgrib2 new.grb -ijlat 1000 1000
experimental space_view2ll scan=12
1:0:(1000,1000),lon=-27.386283,lat=-24.929402,val=0
If the grid point is off the earth, a lat-lon of 999 is used.
The convention of (i,j) is different that used by EUMETSAT. (1,1) is
the bottom left corner which is consistent with wgrib2 convention.
Regridding the data
To space view perspective is not as convenient as a latitude-longitude grid
for many plotting programs. You can use the -lola option to regrid the
data to a lola grid.
* converting to lola grid by nearest neighbor
-sh-3.00$ wgrib2 new.grb -lola -60:1201:.1 -60:1201:.1 lola.grb grib
experimental space_view2ll scan=12
experimental space_view2ij
1:0:d=2011032809:CLOUDM:no_level:-1 missing fcst:
* the grid of lola.grb
-sh-3.00$ wgrib2 -V lola.grb
1:0:vt=2011032809:no_level:-1 missing fcst:CLOUDM Cloud Mask [-]:
ndata=1442401:undef=0:mean=1.53046:min=0:max=3
grid_template=0:winds(N/S):
lat-lon grid:(1201 x 1201) units 1e-06 input WE:SN output WE:SN res 48
lat -60.000000 to 60.000000 by 0.100000
lon 300.000000 to 60.000000 by 0.100000 #points=1442401