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20020417: NIDS conversion from binary to ascii (cont.)



>From: "Emily K. Grover" <address@hidden>
>Organization: Penn State
>Keywords: 200204171535.g3HFZ9a22421 NEXRAD Level III ASCII

Emily,

>Thank you for getting back to me.  Can you give me any information
>about what is in the header of the files?  For example, the header of a
>file looks like:
>
>
>979
>SDUS51 KCLE 162348
>NCRCLE
>
>Most of it it self explanatory (e.g, station, date, time).  I need to
>be able to identify what mode the radar is in.  Where in this header is
>that information?

The format of the NEXRAD Level III files that are being delivered in
NOAAPORT (and, hence, by the Unidata IDD) is not simple.  The beginning
part of the header is not compressed, but the data portion is.  The
best thing I can offer you is the following schematic I used when developing
the McIDAS code that serves the data:

    /*
    ** Copy header bytes to decompression buffer.  The objective is to
    ** create an output buffer that looks like an uncompressed NOAAPORT
    ** NEXRAD product:
    **
    **   Section               Product               Example             End
    **            +--------------------------------+
    **            |                                |
    **      1     |        start of product        | CTRL-A              \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      2     |        sequence number         | 237                 \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      3     |          WMO header            | SDUS53 KARX 062213  \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      4     |             PIL                | N0RARX              \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      5     |                                | AAO130006R2 CH-1
    **            |                                | Interface Control
    **            |             CCB                | Document (ICD)
    **            |                                | for the NWS NWSTG
    **            |                                | Figure 7-1 p 38
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      6     |          WMO header            | SDUS53 KARX 062213  \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      7     |             PIL                | N0RARX              \r\r\n
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **            |                                |
    **            |                                |
    **            |                                |
    **      8     |            image               |
    **            |                                |
    **            |                                |
    **            |                                |
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **      9     |            trailer             | \r\r\nETX
    **            |                                |
    **            +--------------------------------+
    **            |                                |
    **     10     |     Unidata floater trailer    | \0\0
    **            |                                |
    **            +--------------------------------+
    **
    ** Sections 5-8 are zlib compressed.  They must be uncompressed and
    ** read to find out where the image begins.  When this is done, sections
    ** 5-7 are thrown away and 8 is returned immediately following 4.
    ** Section 9 and, if it is there, section 10 are also thrown away.
    **
    */

If you are planning on writing your own routine that will read the
product and then dump ASCII values, then you should get a copy of the
AAO130006R2 CH-1 Interface Control Document (ICD) for the NWS NWSTG
that is published by NOAA.  A good place to start looking for this
document is the 'NOAAPORT Users Page':

http://205.156.54.206/noaaport/html/noaaport.shtml

Look through the downloadable PDF files accessible from the
'NOAAPORT Reference Documentation' link on the above page.

Good luck with your project.

Tom