Re: EASE Ice Motion Vectors

Hi Graham,
I don't have any experience reading in EASE binary files, so I don't
know if you are reading them into NCL correctly or not. However, I
notice that you are saying that the binary files contain short values.
To plot them appropriately in NCL you will need to convert them to float
or double values. Do you know if the data has any add_offset and/or
scale_factor values (common in arrays where short values are stored)? If
so, you should set them as attributes (along with any other information
about the data, including units), and then convert the array to float
using short2flt:

dataT=fbindirread("icemotion.mean.jan-dec.1978-2006.s",0,-1,"short")
dataT@add_offset = 101.2 ; fictional setting
dataT@scale_factor = 0.01 ; fictional setting
dataT@units = "m/s"
data = short2flt(dataT)
delete(dataT)

http://www.ncl.ucar.edu/Document/Functions/Contributed/short2flt.shtml

Hope that helps.. Adam

On 10/02/2012 07:56 PM, Graham Simpkins wrote:
> Thanks Will.
>
> I've attached the code I'm using to read in the binary ice motion and lat/lon data, and then plot. I'm very new to NCL (coming from Matlab), so I apologise if I've made a really stupid mistake; I have tried plotting in Matlab too and I seem to get the same problem, so perhaps it is the way I'm reading in and handling the binary arrays...
>
> I have set the lat2d and lon2d attributes, but whenever I add the "triangularmesh" resource, it fails to plot anything and comes up as "zero field" on the figure.
>
> ________________________________________
> From: whobbs [Will.Hobbs@utas.edu.au]
> Sent: Wednesday, 3 October 2012 11:14 AM
> To: Graham Simpkins
> Cc: ncl-talk@ucar.edu
> Subject: Re: EASE Ice Motion Vectors
>
> Graham
>
> I've worked a fairly extensively with the NSIDC ice motion vectors on NCL, without problem. Without seeing your script then it's difficult to know where your problem lies: I assume you've seen the EASE grid example on the NCL examples (i.e. http://www.ncl.ucar.edu/Applications/ease.shtml)?
>
> Although that example is for a scalar rather than a vector, the same approach to plotting works, i.e. set the trGridType resource to "triangularmesh", and set the data arrays lat2d and lon2d attributes.
>
> If you're already plotting using this approach, it may be something to do with how you're handling the binary arrays; have you, for example, looked at any of the data values for the Ross Sea to see if the actual numbers are inconsistent with climatology?
>
> Will
>
> ----- Original Message -----
> From: Graham Simpkins <g.simpkins@unsw.edu.au>
> Date: Tuesday, October 2, 2012 16:14
> Subject: EASE Ice Motion Vectors
> To: "ncl-talk@ucar.edu" <ncl-talk@ucar.edu>
>
>
>> Hi all,
>>
>> I just wondered if anyone has been able to successfully (and correctly) plot EASE-grid ice motion vectors from the NSIDC for the Antarctic region?
>>
>> I have obtained climatological U and V fields for the southern hemisphere from the binary files. I can plot these as vectors, but the resultant figure is not correct, i.e. it differs rather substantially from previously published ice climatologies, and those figures available at NSIDC. For example, in the Ross Sea region, the flow is southward instead of northward...If anyone has any advice on how to go about plotting this data it would be much appreciated as I'm not sure why it is doing this. All I'm doing is simply extracting the data from the binary files and plotting.
>>
>> I also saw in the archives that an ncl function is available to convert the original binary format to netcdf (http://www.ncl.ucar.edu/Support/talk_archives/2007/1799.html). Does anybody know where this is available from? I can't seem to find it anywhere.
>>
>> Thanks in advance,
>> Graham
>
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-- 
______________________________________________________________
Adam Phillips                                asphilli@ucar.edu
NCAR/Climate and Global Dynamics Division       (303) 497-1726
P.O. Box 3000				
Boulder, CO 80307-3000    http://www.cgd.ucar.edu/cas/asphilli

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Received on Wed Oct 3 12:39:01 2012