ASTER Satellite Data and Silcast
The global ASTER DEM is available
A Global one-second (~30m) DEM mosaic, version 2, from 83S
to 83N, built from 1.4 million ASTER scenes, is now available.
I do not expect the 30m data spacing to be a substantial loss of data
quality form the 15m product.
People who want visual and IR bands will continue to order
This page, when complete, will discuss my experiences (helpful hints and
all that) with ASTER images and the silcast program. It will will also
serve as an index to my raw and processed images, making them
available to everyone with whom I have permission to share.
My SILCAST prohibits distribution of products to third
parties, which I take to mean those outside the University of Washington.)
Anyone in the department can contact Harvey directly.
Silcast produces 15-meter DEMs (doing some oversampling) for individual
images. Adjacent DEMs will not match perfectly.
As of April 1, 2016 ,
all ASTER scenes are free.
Go to NASA
and request L1A Reconstructed Unprocessed Images. Enter the geographic range.
Most people will want to specify daytime images. Click the Search button and
wait 3-10 minutes for the list of matching images to appear.
Make sure that your page is configured to
show the cloud cover (not always accurate) for each quadrant of the image.
If in doubt about coverage, open the browse image in another tab.
Check the images you want and continue to the next page. Click on ordering
options and select FTPpull.
Files are available as hdf or geotiff. I have been downloading as hdf, as
I have never tried geotiff as input to silcast.
Files will typically be available for download in several hours. The name
of the file begins with LA1_003, followed by the date and time of image
acquisition, following by the date and time of processing. There will
be a binary .hdf file and an ascii .met metadata file.
We in ESS are fortunate in having a license to process these files in house.
To process the raw files, you need
Start by dragging the Silcast icon onto the IDLrte icon. Within a minute,
a splash window will appear. Click the button and a menu bar will appear
after several seconds. Select "DEM+Ortho". A window will appear in which
you will select your .hdf file. The the main configuration window will
appear. You can process all 14 bands, but I usually select VNIR (visible
ad near infrared). If you select a different option, you must deselect "All".
At the bottom, you can enter the full pathname and root of the output files.
Entering this info into the box and tricky, so it is easier to browse.
You can give the output file any name, but I like to use the date/time.
Silcast may take about ten minutes to process the image. It will create a
directory containing one geotiff file for each band (including 3R, the
back-looking near-IR band) and VH elevation file. (If you create shortwave
and thermal images, there will also be DEMs at the resolution of those files.)
The view the images in ArcMap, you must use the composite tool to build a
three-band img file.
- silcast software. I have version 1.10 (There is a different numbering
scheme for releases.) loaded on brook, ray, and prism.
(Version 2.00 is out, and we are considering the $700 upgrade.)
- the idl runtime library. I had trouble loading version 7.0, but 6.4 was
easy and sufficient.
- the USB license dongle. See Harvey for this.
There does not seem to be a way to make the dongle work under WIN7.
Browsing for input and output files within silcast can be tedious, as it
always requires full pathnames and browsing starts at the desktop.
A few unix csh commands can create a list of files to copy and paste into
the silcast windows. For example:
@ count = 1
foreach fil (*hdf)
set root = `echo $fil | cut -c5-7,12-25`
@ count = $count + 1
Obviously, the pathnames will vary.
The root name is arbitrary. You can follow the convention of putting each scene
in its own directory, or you can put them in the same place.
You can keep the NASA names or you can give them names like
north, south, lastyear or wickersham.
I have chosen to preserve the time of image
acquistion (MMDDYYYYHHMMSS). Note that successive images differ by
I like to run this command in cygwin,
which runs under windows. It works only under a form of the C shell
(e.g. csh or tcsh), which can be reached from the Bourne shell (usually the
default) with "csh" if it was part of the unix/cygwin installation.
Paste these commands add a csh prompt in a directory containing your
hdf files. An example of the output would be:
For the first file, You would paste the pathname into the silcast input window
and paste the next line into the silcast output window.
Output files would be
Files at the University of Washington Department of Earth and Space Sciences
Contact Harvey to access these files, within the bounds of ASTER and SILCAST licensing.
- Gail's imagery:
|Gail Yamada compiled and indexed many scenes and DEMs before leaving the University.
Harvey has explored the Tsangpo and Siang scenes, and incorporated them in the atlases
used in the Tsangpo Expedition and the 2008 Siang expedition. Some work was also done with
Carajas (ASTER_DEM20020717160053.hdf), SE Brasil and Hammersley.
- More scenes were acquired for the Siang.
sample atlas page
- Olympics Mountains, for spectral anlysis of clearcut by Karen Hutten, NPS.
- Devon Island (for Sanjoy Som)
- Tierra del Fuego, for use with SAR ice-velocity maps.
- Parts of Antarctic Peninsula, for use with SAR ice-velocity maps.
- Central Chile for Phillippe Ruprecht's volcano studies
- Matanuska (Alaska) scenes for the basis of
"Late Quarternary Megafloods from Glacial Lake Atna, Southcentral Alaska, U.S.A.",
submission #129017 to Science
- Scenes of Mount Redoubt.
- Pack Forest, Washington. AST_L1A_00308142002191448_20090428205300_26310.hdf
- Scenes of Croatia for topographic and sprectral analysis of karst by Gabe Casale and Marijana Surkovic
- Dry Valleys of Antarctica (including night and cloudy scenes)
- Kuril Islands
- Mount Everest AST_L1A_00310232003045929_20090616120515_27260.hdf
Note to Adam
I went ahead and imported the data because this is the first image that anyone ordered in both formats. This is interesting:
a) Arcmap can read the HDF file directly. That gives you the 4100x4200 pixel VNIR data at sensor resolution, with an affine transformation to approximate lat-long space. If you zoom in, you see that pixels are tilted.
b) The tiff files are that you ordered are the same size. They are displayed a few pixels out of register with HDF layer.
c) When 3 tiff images are composited into a gridstack, they are 4934x4200 pixels as a tilted rectangle in a square edged with no-data cells.
d) When 3 tiff images are composited into an img file, there are 4100x4200 pixels, and they are rectangular.
e)When the HDF files are processed by silcast, they are projected to UTM and orthorectified. They are 4992 by 4776 pixels as a tilted rectangle within another rectangle. The image bands and the DEM cover a smaller area than the raw image. Only HDF files can be input to silcast.
Harvey Greenberg . . . . .
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