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20010925: Two McIDAS Questions



>From: "J.D. Cetola" <address@hidden>
>Organization: NCSU
>Keywords: 200109251800.f8PI0N120779 McIDAS IMGREMAP AXFORM

Jeff,

>I have two (what I hope are) fairly simple McIDAS questions.
>I am attempting to ingest satellite and radar imagery into a mesoscale
>model (MASS) in an effort to come closer to reality in my simulations.  In
>order to do this, I am using the McIDAS commands IMGREMAP (to map the data
>into polar stereographic format) and AXFORM (to write to ascii so I can
>use the data in the model preprocessor) in an effort to accomplish this.

OK, sounds good.

>My questions are as follows:
>
>1.  I successfully remapped the satellite image and used AXFORM to write
>the data to ascii (I am trying to retrieve the cloud top temperatures).
>AXFORM created four files -- a temperature file, a lat file, a lon file,
>and a header file.  The header file includes an SSEC Navigation Block
>section where non-zero information is provided.  What are these
>parameters?

>The file  lists: 1. PS 2. 1    3. 10000   4. 400000  5. 6000
>6. 780000   7. 6378388   8. 81992   11. 900000

The parameters listed are those needed for the McIDAS navigation module
for Polar Stereographic projections.  The meaning of the parameters is
as follows:

        your
word    value     meaning
-------+---------+--------------------------------------------------------
1.      PS        Polar Stereographic projection
2.      1         image line of the North Pole
3.      10000     image element of the North Pole
4.      400000    standard latitude, [DDDMMSS]
5.      6000      spacing at standard latitude [M]
6.      780000    normal longitude [DDDMMSS]
7.      6378388   radius of the planet [M]
8.      81992     eccentricity of the planet * 1000000
9.                coordinate type, >=0 planetodetic, > 0 planetocentric
10.               longitude convention, >=0 west positive, <=0 west negative
11.     900000    pole latitude [DDDMMSS]
12-120            (reserved)
121-128           memo entry; up to 32 characters of comments

>I know from IMGREMAP the PS is for polar stereographic, the 400000 is
>likely the standard latitude, the 6000 may be resolution im meters, and
>the 780000 is likely standard longitude.  Is there any documentation that
>would tell me what these values are?  I believe I need this information
>before I can write a reader for the preprocessor to access the temperature
>file and properly map it to my I,J grid.

I could not find detailed listings of the exact meanings of navigation
words in the current version of the McIDAS Programmer's Reference
Manual.  The values above are from an old copy of the same that, to my
mind, had a lot more useful information than the current one.  I will
but SSEC about this glaring omission (or be directed by them to where
the information really is).

>2.  My next questions involves radar imagery.  Can I use the same process
>in McIDAS to convert radar imagery to Polar Stereographic and ascii text
>so that I can use it in the model preprocessor?

The procedure you used will work for any image data understood by McIDAS.
For the NEXRAD Level III products (the free radar imagery available through
the IDD), the projection will be local stereographic.

>Secondly, it is my
>understanding I can not use the same process of requesting data as I did
>for satellite imagery (requested through ssec/wisc.  Will data I request
>from NWS or NCDC work in McIDAS?

If I understand you correctly, the answer is yes.  The NEXRAD Level III
products available by FTP from the NWS FTP site is usable in Unidata
McIDAS.  There may come a time (if not now) that a new product that is
made available on these FTP sites is not supported by McIDAS.  If/when
that becomes the case, we need to know so we can update the NEXRAD
Level III product server to support the new product(s).

If you are referring to some imagery than NEXRAD Level III products, then
I would need to know which ones before being able to say whether or not
McIDAS will work with them.

>Any help you can provide will be greatly appreciated.

Please let me know if the above does not provide the information you need.

>Many thanks,
>Jeff.
>
>**********************************
>Jeffrey D. Cetola
>PhD Candidate NC State University
>address@hidden
>address@hidden
>(919) 515-1437
>**********************************

Tom Yoksas


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