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Re: [ferret_users] Sea area demarcation

Hi -
If you want to flag your data according to whether it's over land or sea, you can use a topography/bathymetry data set as Ryo suggested, and create a land/sea mask. There are a couple of higher-resolution data sets I know of which are available via DODS. For example using the ETOPO 5-minute data set, we can make a mask which is 1 where there is water, and missing over land.

set data "http://www.ferret.noaa.gov/cgi-bin/dods/nph-dods/data/etopo5.nc";
let mask = if rose lt 0 then 1
shade mask

! To work with this and your data, regrid the mask to the grid of your data, and multiply.
! If your data were in a file called my_data.nc, and a variable called var:

cancel data/all

set data "http://www.ferret.noaa.gov/cgi-bin/dods/nph-dods/data/etopo5.nc";
set data my_data.nc

let mask = if rose[d=1,gxy=my_var[d=2]] lt 0 then 1
set region/x=80w:55w/y=65n:80N

shade mask * var

For finer detail, I was going to suggest the Smith-Sandwell data, which is available via DODS, but this data set does not go farther north than 72 degrees. Does anyone on the list have a suggestion for topography data in the far north?

set data "http://ferret.pmel.noaa.gov/cgi-bin/dods/nph-dods/data/PMEL/smith_sandwell_topo.nc";


Juanxiong He wrote:

Dear all,
I would like to know where I can find the sea area demarcation data, such as the boundary line between Arctic Archipelago and Baffin Bay. It's a terrible thing to using eyes identifying the boundary line poin by point.

Thanks in advance!


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