GRIPS 2: Government Rast…rocessing Software & Data/GRIPS_2.cdr/readmes/hub_lsat.rmf

Text File | 1990-06-20 | 6KB | 120 lines

                         HUBBARD GLACIER
                      THEMATIC MAPPER DATA

In early June 1986, the advancing face of Hubbard Glacier, located
in Southeastern Alaska, closed off the entrance to Russell Fiord
with an ice dam that created the world's largest known modern
glacier-dammed lake.  A location map of the Hubbard Glacier area
is provided on this disk in an image file named HUBMAP.DAT.

Over 70 miles long, the Hubbard is North America's largest
tidewater glacier.  The Valerie Glacier, a tributary to the
Hubbard, moved at rates of up to 130 feet per day causing the
Hubbard to advance more than a mile during the Summer of 1986.  The
current advance is part of a long-term cycle of advance and
retreat.  About 800 years ago, the glacier extended all the way to
the mouth of Yakutat Bay. Over the next several hundred years this
cycle may be repeated.

Because of the ice dam, Russell Fiord became a lake and water level
rose at a very rapid rate during the summer months.  Marine mammals
(porpoise and seals) and other marine life were trapped.  If the
lake had continued to rise, it was predicted that it would overflow
to the south within a year.  The dam formed by the surging glacier
broke on October 8, 1986, restoring the dammed-up lake to a fiord,
and recovering the vital sea-water environment for the marine life.
It is expected that the glacier will continue to surge and form
another dam in the future as the cycle continues.

Satellite images were used to monitor the movement of the Hubbard
Glacier and the increase in the size of Russell Lake.  The images
on this disk are portions of Landsat Thematic Mapper scenes
acquired over southeastern Alaska on August 7, 1985 (4100 lines x
3040 samples), and September 11, 1986 (4100 lines x 2932 samples).
The area around Hubbard Glacier was extracted from the Landsat
Thematic Mapper digital data and spectral bands 4, 3, and 2
composited into an 8-bit image with an associated color lookup
table to convey the appearance of a color infra-red image.  The
data have not been geometrically corrected or registered to any map
base.  The color composited raster image files for the two dates
are on the disk as HUB85.DAT (the associated color lookup tables,
or palette file, is HUB85.PAL) and HUB86.DAT (color palette
HUB86.PAL).  In these images healthy vegetation are shown in shades
of red, water appears as shades of blue and black, and ice and snow
appear white.  A snow mask was applied to both data sets to enhance
details in the ice and snow covered areas.  The individual
satellite bands have also been provided on this disk.  These bands
are named HUB85_4.DAT, HUB85_3.DAT, and HUB85_2.DAT for the August
1985 bands 4,3, and 2.  The bands of satellite data collected in
September 1986 right before the ice dam broke are named
HUB86_4.DAT, HUB86_3.DAT, and HUB86_2.DAT.
All three bands for both dates were mapped (contrast stretched)
using the following values:

        RED    From: 0 17 110 220 255
            To:   0  0 175 245 255

        GRN    From: 0 12  80 170 235 255
            To:   0  0 175 215 255 255

        BLUE    From: 0 17  80 170 231 255
            To:     0  0 175 215 255 255

DATA FORMAT

All satellite image files for the Hubbard Glacier are fixed length
8-bit byte records.  Each fixed physical length record maps
directly to the logical image line length.  The file format is
consistent with NASA's IMAGE Object Format used as a standard
published by NASA's Planetary Data System (PDS) group. This image
interchange format is documented in NASA's Jet Propulsion Lab (JPL)
document D-4683. The format allows inclusion of the label records
describing the image at the front of the file, or as a seperate
label file.  To facilitate use of the Hubbard images by other
systems than those supporting the PDS interchange format, all
Hubbard Glacier label records on this disk are found in a seperate
file whose file name is the same as the DAT file where the actual
image data are stored, but the file extension is LBL.  For example,
the HUB85.DAT image file contains raster data values only.  Its
associated HUB85.LBL label file contains all descriptive
information about that image that is required by such image display
systems as JPL's IMDISP public domain PC image display software.
The user can then access and display the image without knowing
details about image size or data type.  Those users who wish to
access the image on other raster image processing systems can print
out the label files to get the descriptive information they need
to build any system specific header files for the system they are
using.


DEMONSTRATION INSTRUCTIONS

If you want to take a quick look at the TM images for the Hubbard
area using the IMDISP program provided with this disk, follow these
steps:
     1. Change to the disk designation where your CD-ROM disk is
        loaded (usually L:).

     2. Make sure the IMDISP floppy disk is in your A: drive and
        start the automated demo display program by typing:

             SET IMDISP=PARADISE  or  SET IMDISP=ORCHID

        (whichever is appropriate for the graphics card in your PC)

        then type:

             A:IMDISP DEMO.CMD

        (This will run the IMDISP batch command file to display the
        August and September Hubbard images sequentially and label
        geographic feature names on the screen, then display the
        TM band 7 images for 1985 and 1986 side by side).

     3. After the two date comparison images have been displayed,
        try the HELP FILE and HELP DISPLAY command to see what
        other IMDISP features you can use to take a closer look at
        the Hubbard images.

     4. Type EXIT when you have finished using the IMDISP program.