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 individual scenes.

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.

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)
   echo $count
   set root = `echo $fil | cut -c5-7,12-25`
   echo y:\\\\topog\\\\areas\\\\russia\\\\aster\\\\$fil
   echo y:\\\\topog\\\\areas\\\\russia\\\\aster\\\\$root\\\\$root
   @ 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 9 seconds. 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. More observations

Web Curator: Harvey Greenberg . . . . . about this site . . . . . What's New . . . .sorry