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[Datastream #XQI-115437]: unidata imagery data stream

Hi Julia,

> I am using McIDAS to access unidata2.ssec.wisc.edu. There are 3 groups:
> GOESEAST, EAST, and WEST. I found out that the area files are different
> among these three groups.

That is correct.  The EAST and WEST datasets are composed of multibanded
images. The GOESEAST dataset is composed of single-banded images.

Please note that all of the IR images in the GOESEAST dataset are identical
to the ones sent in the Unidata-Wisconsin IDD datastream (UNIWISC).  They
are also available from the RTIMAGES dataset on several servers.  The only
image that is significantly different is the 1 km Visible one.  The Visible
images sent in the Unidata-Wisconsin datastream have all been blown-down
to an effective 4 km resolution.

> For example, area files of band 1 from EAST or
> WEST are GVAR/RAW file with 2 bytes/pixel, while the area file of band 1
> from GOESEAST is VISR/BRIT file with 1 byte/pixel. Can anyone explain the
> difference among them?

The EAST and WEST datasets are populated by GOES ingest machines.  The
images are all 10-bit and are oversampled in the element dimension.

The images in the GOESEAST dataset are created from images in the EAST and
SOUTH datasets (SOUTH is hosted on goessouth.unidata.ucar.edu; it contains
realtime images from GOES-10 which is now being used to scan South America).
The GOESEAST images have the element oversampling removed (MAG=1 -2) and
have been converted in to 8-bit (1-byte) images.

> When using IMGDISP EAST/CONUS.0 1 BAND=1, the satellite image was not
> displayed.

This is strange.  Perhaps you tried loading the image when one would not
expect Visible data because it was dark?  I just tried loading the VIS
band (BAND=1) from the latest EAST/CONUS image and I also got a blank.
The IR images were fine, however.  This will take some more investigation
on my part.

> But IMGDISP GOESEAST/WH-4KVIS.0 1 BAND=1 can. Is it because
> EAST/CONUS.0 is a GVAR/RAW file?

No. The use of the different types of images in McIDAS is transparent.

> When using AXFORM to convert EAST/CONUS area file to ASCII, is the digital
> count converted directly from the 2-byte raw data? Or from the 10-bit
> value?

The two-byte data _IS_ the 10-bit data.

To answer your question, however, I must point out that AXFORM works on
local AREA files.  If the AREA file you are dumping values from has 10-bit
data, then AXFORM converts the counts from the 10-bit data.  If the AREA
file you are working with contains 1-byte data, then AXFORM is converting
the 1-byte data.

> In the document of
> McIDAS data structure, it specifies that GVAR data has 10 bits formatted
> as:
> |0|x|x|x|x|x|x|x|x|x|x|0|0|0|0|0|

Correct.  Images tagged as GVAR should contain 10-bit data.  Images tagged
as VISR should contain 1-byte data.

> Thanks,

No worries.


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Ticket Details
Ticket ID: XQI-115437
Department: Support McIDAS
Priority: Normal
Status: Closed

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