TMSB Tutorial 2: OnEarth Satellite Imagery

article by Ben Lincoln

Once you've familiarized yourself with using The Mirror's Surface Breaks using the instructions in TMSB Tutorial 1: Basic Use, you're ready to proceed to using the same general technique to process imagery from NASA's OnEarth website.

For the most part, the process is very similar. The main body of this article was going to be about how to obtain the source data for yourself, but unfortunately NASA shut down the non-tiled OnEarth WMS service (apparently indefinitely) around the beginning of 2011. If anyone knows of a way to obtain this type of image data now, in a losslessly-compressed format (PNG or TIFF preferred), please let me know.

Dear NASA staff: can you please turn that functionality back on? It was really great, and one of the few places that ordinary citizens could get ahold of losslessly-compressed mid-infrared and thermal images, among other things.

OnEarth Image Data

Prior to being shut down, the following distinct layers of satellite data were made available by the OnEarth server:

Microwave RADAR reflectance, from the Shuttle Radar Topography Mission
Elevation data with a resolution of 90m, derived from the SRTM data
Elevation data with a resolution of 30m (confined to the area within the borders of the United States)
Thermal infrared in high- and low-gain variations (from LandSat 7)
Two mid-infrared bands (from LandSat 7)
Near infrared (from LandSat 7)
Red (from LandSat 7)
Green (from LandSat 7)
Blue (from LandSat 7)
Panchromatic - a swathe from blue to near-infrared (from LandSat 7)

For more information on the specific LandSat 7 wavelengths, see the list near the end of the Calculated Greyscale Images article. The SRTM data is an unspecified combination of C- and X-band RADAR reflectance.

In keeping with the conventions used in the OnEarth URLs, the TMSB configuration which uses them uses this naming convention for the input files:

Elevation = either the 90m or 30m data, as determined by the user who saved the file
SRTM = SRTM RADAR reflectance image
ThH = high-gain thermal infrared image
ThL = low-gain thermal infrared image
IR3 = longer-wavelength (2220nm peak) mid-infrared image
IR2 = shorter-wavelength (1625nm peak) mid-infrared image
IR1 = near infrared image
Red = red image
Green = green image
Blue = blue image
Pan = panchromatic image

Working With OnEarth Data in TMSB

In order to fit in with the TMSB processing model, all of the images mentioned above are treated as "spectral bands", even though elevation is not a spectral band. This is a lot of source data, and if you include all of these bands in your input directory, you will generally end up with an extremely large number of input permutations. Therefore, there are three recommendations for cutting the number down a bit:

Leave out the elevation image unless you're really sure you want to include it.
If you are including the elevation image, consider using one of the "Alternate" satellite data configurations, which only allow elevation to be used as the luminance channel, as opposed to one of the channels in three-channel false colour images.
Include only one or the other of ThH and ThL. They are the same data, really, except that one has been amplified more. Generally, this means that one of them will be a "good" image, and the other will either be "blown out" or extremely dark. Remove the poorer-quality of the two from the input directory.

Once you have your source images, the process is the same as in The Mirror's Surface Breaks, with the following exceptions:

You'll need to select one of the OnEarth input configurations, or TMSB won't do anything useful.
You should consider using a processing configuration that generates fewer permutations, at least at first. Especially if you are running low on disk space.
You'll be able to use (effectively) the satellite-imagery-specific processing configurations, and also usually obtain more (or at least different) results from the general-purpose configurations. For example, the vegetation index processing configurations will generate a lot more variations (due to the mid-infrared data), including the mysterious "tasseled cap" images.

OnEarth Processing Screenshots

Your source directories should look something like this

Be sure to select an OnEarth input configuration!

New and exciting processing configurations can be used

Processing satellite imagery

Download
File	Size	Version	Release Date	Author
Big Bend National Park	47 MiB	1.0	2011-02-21	NASA
A sample OnEarth image set for use with the TMSB tutorials. This set will generate output images that occupy about 20 MiB on disk for each variation in the selected processing configuration.

Download
File	Size	Version	Release Date	Author
Yellowstone National Park (And Cody, Wyoming)	67 MiB	1.0	2011-02-21	NASA
A sample OnEarth image set for use with the TMSB tutorials. This set will generate output images that occupy about 25 MiB on disk for each variation in the selected processing configuration.

Download
File	Size	Version	Release Date	Author
New York City (and Surrounding Area)	9 MiB	1.0	2011-02-21	NASA
A sample OnEarth image set for use with the TMSB tutorials. This set will generate output images that occupy about 5 MiB on disk for each variation in the selected processing configuration.

Download
File	Size	Version	Release Date	Author
Egypt (near Luxor)	13 MiB	1.0	2011-02-21	NASA
A sample OnEarth image set for use with the TMSB tutorials. This set will generate output images that occupy about 5 MiB on disk for each variation in the selected processing configuration.

Download
File	Size	Version	Release Date	Author
Global View of the Earth	4 MiB	1.0	2011-02-21	NASA
A sample OnEarth image set for use with the TMSB tutorials. This set will generate output images that occupy about 2 MiB on disk for each variation in the selected processing configuration. Note: not all spectral bands contain the full global view, so you may experience a "patchwork" effect.