Getting and Using Satellite
Access raw LANDSAT satellite imagery and use it for graphical work.
By Ryan Foss
This tutorial describes how to get raw Landsat
7 satellite data from NASA repositories and convert it into
usable, full color imagery.
Obtaining Raw Landsat-7 Data
First you have to find your area of interest. Go to the
Science Data Interface (ESDI) and click on Map
Search. Map searching will allow you to browse
the world for various image data using an interactive map.
Since you want to search the datasets for Landsat-7 image
data, check the ETM+ checkbox on the upper left.
The Map Search Tool makes it easy to find image
data. The tool is pretty self explanatory, so just
try it. The easiest way is to just click the map until
you're close, then select the arrow+ icon and click
What you will end up with is an area selection similar
to Figure 2.
Now click on the Preview & Download
button to get access to the image datasets. If there
is more than one dataset available, you'll need to
select one that fits your desires, either by date
or area coverage. Select the dataset by clicking the
[ID], then click the download button. This will bring
you to direct FTP access to the image data.
Figure 1. The Map Search tool at the ESDI web site
makes it easy to find image data.
Landat-7 is a multi-band satellite, thus the data
is represented with multiple grayscale images, each
representing different spectrums of light. Since we
want a true-color image, we need to work with the
visible spectrum. You'll need to download three images,
each representing the basic color spectrums of an
RGB image, red, green, blue.
The names of the images may seem confusing, but what's
important is the number at the end of the filename.
Figure 2. Single band image from a Landsat-7 dataset.
Download the first three bands (files ending with numbers
10, 20, and 30), uncompress them and open them in Photoshop.
Without getting to much in the details, you'll want to download
files that look similar in format to these. They (most likely)
are compressed TIFF files, so you'll need a program such
as WinZIP or WinRAR to extract the images.
FYI, the file names are actually useful, corresponding to
Path and Row information, satellite and capture date. The
image dataset above, p027r029 is path 27, row 29. This makes
it easy to find the dataset again, if you should need to come
back to it.
Combining Bands into True Color
Each of these bands represents a basic spectrum
of color. We need to combine them to produce a true color
Band 1 is Blue
Band 2 is Green
Band 3 is Red
|With the three images open in Photoshop, go to the
channels pallet. Using the little triangle icon on the
right, select “Merge Channels”. Merge the
channels into a 3 color RGB image. Set the bands appropriately,
3 is red, 2 is green and 1 is blue.
Figure 3. Photoshop channel pallet.
Note: There is another method to combine bands.
Essentially, open each image and copy paste it into the
appropriate color channel. Here’s step by step how
to. Open the band 3 image and convert it to RGB via Image>Mode>RGB
Color. Open band 2 image and select all (Ctrl-A) and copy
(Ctrl-C). Close the band 2 image and go to the Channel pallet
of the band 3 image. Select the Green channel and paste.
Open band 1 and repeat the process, copy it to the Blue
This is the most difficult step. Depending on the quality
of the images from the satellite, and other factors like
time of day or haze. Regardless, you'll most likely want
to adjust the color. Image>Adjustments>Auto Color
usually does a decent job.
There you have it. This image data is in 30m data. This means that
each pixel represents approximately 30 meters length. Not really
good, but does well for large areas. This can be improved upon by
using Band 8, the panchromatic band, to effectively double the resolution
to 15 meter. I outline the methods in the next tutorial: Doubling
Landsat-7 Image Resolution.
If you’re interested in better resolution imagery, then you’re
going to have to pay a service.
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