THIS IS A DRAFT
This document is intended
to help users find, download, and use free Landsat
data for almost any land surface
in the world using a freeware
software program, MultiSpec©.
Free Software | Getting the Free Data |
Using Compression Software | Preparing
the Thermal Band | Linking Bands
of Data | Subsetting Images
for Smaller File Size | Helpful Tips
General Note: When following the steps in this tutorial, it may help you to read all the notes about each step before taking it.
Many professional and educational programs use satellite data
and images to study our changing Earth. In particular, the Landsat
Program has provided over 30 years
of calibrated high spatial resolution data of the Earth's surface
to a broad and varied user community, including agribusiness,
global change researchers, academia, state and local governments, commercial
users, military, and the international community. This uninterrupted record
provides abundant opportunity for "before and after" comparisons
of Earth's land surface throughout the past 30 years.
To read more about Landsat data and its uses please visit http://landsat.gsfc.nasa.gov
For details about the data and use of the data please examine the Landsat Data Users Handbook.
This tutorial provides instruction on how
to obtain and import free Landsat data
into a free software program, make subsets of the
data, and create images that can be used to examine change over
The data used in this tutorial are from
the Global Land Cover Facility (GLCF)
at the University of Maryland's Institute for Advanced
Computer Studies in College Park, MD. The two data sets (one from circa
1990, and one from circa 2000) cover the entire globe except Antarctica.
Together these data sets constitute the "Landsat
Geocover Data Set."
The free software used in this tutorial
is MultiSpec©, developed at Purdue University, West
Lafayette, IN, by David Landgrebe and Larry Biehl from the School of
Electrical Computer Engineering, Agronomy and Laboratory for Applications of Remote Sensing.
It is recommended that users take the MultiSpec© tutorial
before using the software. The
tutorial is available through the GLOBE program at:
Software Step 1:
http://dynamo.ecn.purdue.edu/~biehl/MultiSpec/ and download MultiSpec ©.
Make sure to download the correct version for your computer.
There are versions for Macintosh and Windows software. MultiSpec© is
updated regularly with additional features. Users who want to conduct
more advanced operations may want to visit the site
and upgrade their software twice a year.
About the Data: Landsat observations of the Earth's surface are divided
into "scenes," each of which is approximately 185 km by 172 km. A
grid system of "paths" and "rows" is used to provide
a reference number for each scene. The satellite is in a circumpolar orbit that
provides repeat coverage of the same area every 16 days. The data used in this
tutorial are orthorectified. Orthorectified scenes are georeferenced, meaning
that if one lays a scene from one locality directly on top of another scene from
that same locality, all of the map locations will match up exactly. This makes
Orthorectified Landsat scenes especially useful for detecting change over time.
More information about change detection is available from NASA's
Landsat Change Detection subset pair web site.
[URL to this will be provided here
prior to publication.]
Data Step 1: Go to the Global
Land Cover Facility's
web site at: http://glcf.umiacs.umd.edu/index.shtml
The Global Land Cover Facility (GLCF) provides Earth science
data and products free to anyone via FTP.
The GLCF provides other datasets in addition to the
one used in this tutorial. The Landsat GeoCover data
set is the subject of this tutorial.
Data Step 2: At the Global Land Cover
Web site, select the Earth Science Data
Interface by clicking on the ESDI image
within the Download
Data option (at right of screen).
Data Step 3: Select the Map Search option.
You can also use the Map Search to browse and query
using an interactive map. You must use the
Map Search when looking for Landsat GeoCover data. The
Map Search will provide two gofer scenes for anywhere in the
United States from around 1990 and 2000. These scenes
are excellent for change detection.
Data Step 4: Select all three instruments from the Landsat
Imagery box (Ignore the other options.)
"ETM+", "TM", and "MSS" refer
to different sensors that have flown on different
Landsat satellites through the years.
The GeoCover 1990 data is Landsat TM data and
the GeoCover 2000 data is Landsat ETM+. Data
from other years may be available for your chosen
geographic location, so select all three instruments.
Data Step 5: Select the "Place" tab.
When looking for data, the place function is the easiest
Data Step 6: Enter the major place name nearest your area of interest.
At the bottom of the new window is a blank
box labeled "Place." In
this box enter a major place (city, for example.)
The database currently contains the following place names that can be searched:
Note: For more information regarding the place name search refer to the "searching tips" available at the Earth Science Data Interface (ESDI) at the Global Land Cover Facility.
Or, click the link directly above where the place name is entered.
Worldwide states, provinces, and equivalent country
administrative units (e.g., Oblasts).
Major world cities.
United States cities with population greater than 10,000 (circa 1998).
Data Step 7: Select Update Map (just below the map).
Note: If you want to change a location you must go back to the world view before proceeding.
Data Step 8: Once a place name has been indicated,
select the Preview & Download
button (just below the map).
When the selection area is displayed, a red square (or a few squares)
will appear on the map, representing the extent of the Landsat scene(s) you
have selected. If your desired location is not in the area covered by the red square(s),
go back and select using "map area" instead of "place."
Note: The Preview & Download option will
not work if no scene has been selected.
In the Preview & Download results window, seen below, there are numerous
features. All of the scenes of the user's selected
location available from the GLCF are listed. Yellowish
highlight indicates a selected scene. A thumbnail
of that selected scene appears at the upper left side
of the screen. (The thumbnail is a false color composite
image (usually a 4,3,2 band combination, which means
that vegetation is shown as red.) Additionally, this
screen includes a reference map indicating the spatial
extent covered by the scene. (The reference map is
especially helpful when there are multiple scenes in
Data Step 9: Choose a Landsat scene (data) from the list.
If there are more than two scenes in the list,
the best scenes to select are the ETM+ (Landsat 7)
scenes. ETM+ scenes if they are available will
result in higher quality images, though a user may wish to
choose data based upon date, depending upon need.
To select another scene in the list, select its
[ID] number or the "Next" button.
A preview image and a table will be displayed at
the top of the Web page.
In the Attribute column, "Ortho, GeoCover" refers
to orthorectified, a process that corrects and improves the geographic
coordinates associated with the scenes.
Data Step 10: Re-sort the list of scenes if desired.
Use the lists [Acq. Date] function to re-sort the list. Click it once to sort the data with the oldest scene/data at top and click again to reverse the order, with the oldest scene/data at bottom.
Data Step 11: Choose the desired scene (for example, the most recent) from the list.
Click on the identification [ID] number to select the scene.
Data Step 12: Open the download page for the selected scene.
Note: In the example below, the downloadable file
is 171 MB. The download rate will depend greatly
on the type of Internet connection being used. Downloading
is a one-time process, and can be done anywhere
with access to a high speed Internet connection.
Additionally, Landsat scenes are separated into
individual files, so each one is not very large.
The process may take some time, but should be manageable. Click the Download button.
Data Step 13: Understanding the file name protocol
At the top of the page you will see the file name for your selected scene; below this you will find a list of file names. The
file names follow a protocol, and contain important information.
The GLCF scene file-naming protocol may appear a
bit complex to a novice user. In our example, the file names
begin with p015r33_5t879516. So what is in the Landsat
data file name?
Landsat 7 orbits the Earth in a preplanned
ground track. The sensor onboard the spacecraft obtains
data along the ground track at a fixed width or
swath. When mapped, the swaths are called "paths." The
concept of path is somewhat analogous to longitude. Thus, p015 stands for
Path 15. Our scene example shows Washington, D.C. Path 14 is to the east, and path 16 is to
the west, of Washington D.C.
r33 means Row 33, which signifies how far
down from the North Pole the scene was acquired. There are no negative rows
5t870516 tells us that the scene is from
Landsat 5, and the date is shortened from 1987, May 16th to 870516.
Note: Our example uses Landsat 5 TM data files (signified by the
5t in the file name p015r33_5t870516). Landsat 7 data files have a L7 in the front of the file name (L71015033),
and Landsat 1-4 MSS data have a 1 to a 4 with an m after it (p016r33_1m1972).
Note that all the files begin with the path/row and date. The remaining portion
of the file names vary as follows:
browse.jpg's a jpeg color composite
hdr is header file, and it is not always included.
met stands for metadata. It is a very important file, especially
if you plan to use the scene in GIS applications. It includes all of the Landsat scene
information specific to how and when this scene was acquired. Additionally, all the processing
and geographic information is included in the met file.
preview.jpg is a smaller version of the browse.jpg image.
The remaining file names represent the Landsat data itself. They are listed in numerical order,
and the number represents the band. For example, nn10tif.gz signifies band 1, nn20.tif.gz
signifies band 2 and so on.
Table 1, "Landsat Data Characterizations for the Various Missions," indicates the bands
of data used by the various Landsat satellites. Notice that the numbers and wavelengths have changed over
time, with different Landsat satellites. Landsat 7 has nine bands of data; Landsat 1-3 have only four bands
Data Step 14: Download and uncompress the selected scene files.
Click on each link and download only one file at a time.
Download all the files and place them in a folder. (It is important that they all
be placed in the same folder.) The data is a compressed TIFF file. The gz at
the end as in, nn7.tif.gz, means that the file is compressed.
Note: The files are quite large (about 50mb each) and may take time to download.
Some files may not automatically download, but may open in your browser or other
image viewing software (such as Preview). In those cases, you must manually save them to
your folder. To manually download and save the files with a Windows program, right-click
the file name and select "Download the Link to Disk" or "Save Target
As." With a Mac, hold down the Control key, "ctrl", and click on the file.
Then select the "Download the Link to Disk."
(This image is from Mac OS X.)
Your computer may give you a message stating that you cannot save
a ".tar" file without ".jpg" at the end. That is OK;
go ahead and allow ".jpg" to be added to the file name.
After each manual file save, use the "Back" button to return to the list
of files to be downloaded if necessary.
Hint: It may help you to keep track of which files you
have successfully downloaded if you copy the list from the Web site and paste
it into a Word document. You can mark each file downloaded
as you proceed through the list.
Once the files are downloaded, most computers will automatically uncompress the files.
If they do not do so, double click the file. The compression software should open and
ask you to uncompress the files.
What if the computer does not open the files?
In this case, your computer does not have compression software. (Most computers do have this software.)
Use the steps below, under "Using Compression Software," to download the software, and then
extract or uncompress the files.
To help with file management, it is recommended that
the user create a new folder for all the data. In educational
settings, the Landsat TM band 6 or Landsat ETM+ bands
of data 61, 62 or 80, are not typically used, so
most teachers or students would not need to download them.
These file names end with either B80.L1G.gz for band 8 (panchromatic) or B62.L1G.gz
62 (thermal). Also note that Landsat MSS data has only four
bands of data (no blue data, but green, visible red and two
infrared bands). More information about the files is available
in Table 1 below.
Example of typical set of downloaded Landsat files:
||Actual Size\ |
|| 61625338 bytes
|| 26405598 bytes
||MSS - MultiSpectral Scanner
||MSS - MultiSpectral Scanner &
ETM+ - Enhanced Thematic Mapper Plus
|Mission coverage dates
||August 7, 1972 to February 7, 1983
||August 17, 1982 to October 1999
||July 1999 to present
||(bands 1-5, 7)
||(bands 1-5, 7)
|Bands (microns, µ)
||(bands 61 & 62)
|Bands (microns, µ)
||10.4-12.5 (Landsat 5 only)
|Bands (microns, µ)
Note: Bands 6, 61,62 and 8 are not typicaly used in an educational setting. Avoid downloading if you don't require them in order to conserve time.
Decompression Step 1: Open the folder on your computer where
the images are downloaded.
Decompression Step 2: Highlight all the files and right-click.
Decompression Step 3: Select the "Extract files" or "Open with WinZip" option
and follow the steps.
Note: Users who do not have the "Extract files" option
will need to download compression software. It is available from WinZip,
Download the Unzip Wizard, which is needed to unzip the Landsat data. Make sure to download the correct version
for your computer.
If you do not
have the compression software, go to Aladdin Systems, Inc. StuffIt Expander for Macintosh
or StuffIt Expander for Windows
StuffIt Expander easily expands, decodes, and unzips the data. Make sure to download the correct
version for your computer.
Decompression Step 1: Open the folder where
the images are downloaded.
Decompression Step 2: Highlight
all the files, hold down the control key and
mouse click. This will open the menu shown below (for OS X platform).
Decompression Step 3: Select the "Open With" option and select "Stuffit
Decompression Step 4: The uncompressed files will be opened
into the same folder.
Note: Compression software is available from Aladdin Systems,
Inc. StuffIt Expander for Macintosh or StuffIt Expander for Windows
StuffIt Expander easily expands and decodes
all the Landsat files you downloaded from the Web. Make
sure to download the correct version for your computer.
If you plan on using all the Landsat bands of data, you will
need to modify band 6 (thermal data) to work with the 30-meter band data.
As noted in Table 1, all Landsat missions had different spatial
resolutions for the thermal band data and the multispectral data. The Landsat 7
MultiSpectral data have a resolution of 30 meters, whereas the Thermal data
have a resolution of 60 meters. Study the images below to see the spatial resolution
differences between the two Landsat bands.
In MultiSpec©, if the 30 meter and 60 meter data are
linked without modifying the 60 meter thermal data, the software
will automatically degrade the other bands of 30 meter data
resolution to 60 meter resolution. Instead, you can use MultiSpec© to
increase the thermal band area and file size to match the other bands,
thus preserving the 30-meter resolution of the data.
Part of Washington D.C. where bridges cross the Potomac
River, in Near Infrared Band 4 (30 meter resolution, upper) and Thermal
Band 6 (60 meter resolution, lower)
Note: Currently the preparation
of the thermal data can be done only in MultiSpec© Mac
versions (as of April 1, 2005). The same preparation
can be done on other platforms using image or photo software such PhotoShop,
by doubling the image size for both lines and columns.
Steps to preparing Thermal band data:
Thermal Step 1: Open MultiSpec©. Open the Thermal band 6 (TM) or
61 (ETM+) band data file.
Go to File>Open Image, then select the thermal band data (example of file name on GLCF:
A box that asks for specifications will appear. Click "OK".
Click "OK" for the next screen as well.
The computer will now compute image statistics and ask you to save this new file.
You must change the name of the file from the default, or
the program will write this file over your original data file. Simply
change the name of the file and save it to your data folder. Now an image
in grey scale will appear
Thermal Step 2: Under the "Processor" menu select "Reformat," and
then the "Rectify Image" option.
Thermal Step 3: The "Set Image Rectification Parameters" window
will open. Change the "Rectification Settings" Scale
to 2 for both the Lines and Columns windows. Click "OK".
Note: this step will take quite some time
to complete if you are doing this for a full scene.
Thermal Step 4: Save the Image in the same folder as the
other satellite images. Remember to save the image with both the date
and the band number. See the example in the image below:
Thermal Step 5: Compare the new image file to the other
data files, and make sure that the new one is the same file size and
also covers the same area (that is, be sure the path and row are the same for each file).
Before the scaling (Thermal Step 4):
After the scaling:
Now the Thermal band is ready to be linked with the other bands.
(Combining Landsat bands into one image file) TOP
Linking Step 1: Open MultiSpec©. Under "File" go
to "Open Image." Locate your downloaded image files (see Data Step 12), and
highlight the blue band (band 1) image file.
(For a description of the file names see Data Step 14: Understanding the file name protocol, above.)
Note: If the image file names do not appear when you open the folder,
select the "All Files" option in the "Files of Type" pull down menu.
Linking Step 2: Click on "open." A box that
asks for specifications will appear. Click "OK."
Click "OK" for the next screen as well. The computer will now compute image statistics and
ask you to save this new file.
You must change the name of the file from the default, or the program
will write this file over your original data file. Simply change the name of the
file and save it to your data folder. Now an image in grey scale will appear. Linking
Step 3: Go back to "File" and again click on "Open Image".
Highlight …B20.tif file name, and before you click OK, click the box beside "
Link to active image window ". Then click "open".
Linking Step 4: Continue this process
until you have opened and linked all the data files. Link them in numerical order
starting with the lowest number (B10, B20, B30, B40, B50, B61, B70). Once all of
the files you need have been opened, click "Cancel".
Open and link only the Landsat data files (example of data file name: L71015033_03320020618_B10.tif),
Avoid linking the other kinds of files, as it will confuse the software.
Note: At the top of the image (see example
above), the file name should read, "L7…" This
signifies that you have linked seven bands together. Make sure
that the number of files you intended to link is the same as the file name shows.
Note: If the images open in separate windows,
the images were opened without the "Link to active image window" box
being selected. Close the windows and restart the linking process from Linking Step 1.
Note: if you want to work with the entire Landsat
scene, save the image with all the linked bands using the reformat
function in MultiSpec©.
(Pull down the Processor menu, select Reformat, then Image File Format).
Now you are ready to subset the scene.
Many users of Landsat data find that they do not need the
entire scene for analysis. Teachers often find that large spatial areas,
especially an entire scene, will overwhelm students and their computers.
If you want to subset an area from a large Landsat image, follow these steps.
Subsetting Single Images
The data files must be linked prior to following the subsetting instructions! See section
above "Linking Bands of Data."
Subsetting: Single Image Step
1: Select the area on the image to be subset.
A recommended area would not be larger
than 2000 pixels by 2000. In MultiSpec© you can see how
large the selection area is by using the coordinate view. Pull
down the "Window" menu and select the "Show
Coordinate View" option.
This will show the Coordinates of the image at the
top. On the top left there is a pull down menu showing the MultiSpec© default
Coordinate View of Lines-Columns.
Using the Coordinate View you can select an area
to subset. The "Number pixels" function gives you a
good clue about how many pixels have been selected. To select an
area, place your cursor at the upper left corner
of the area you wish to select, click the mouse and drag down to
the lower right. The coordinates will change, and the number of pixels in the
selected area will be calculated. For a 2000 by 2000 pixel area
there are 4,000,000 pixels.
Teachers note: If the "number
pixels" is higher than 4,000,000 it may be too large of
an area to work with for students.
Subsetting: Single Image Step 2: Pull down the "Processor" menu,
and select "Reformat." A box will appear; select "Change Image File Format."
Subsetting: Single Image
Step 3: In the "Image File Format Change
Options" window, find the "Header" pull
down menu, and select the GeoTIFF format. (This option
will only work if the Landsat data is originally a
GeoTIFF. The GeoTIFF file format is ideal because
the file header contains all of the geographic information.)
Subsetting: Single Image Step
4: Click "OK". When the next box pops up, don’t change the start and end lines and
columns, but make sure the intervals are set at one.
Subsetting: Single Image Step
5: Click "OK." The
next box to pop up is for you to name and save the multi-channeled image.
Give the image a name such as "name of county" and the date
the image was acquired. End the file name with the file extension ".tif" An
example would be "Seattle_06_23_01.tif" Make sure you are
saving the image to the same file where you have all the previous images. Click "save."
Subsetting: Change Detection Images
The Landsat satellites have been acquiring imagery of the
Earth since 1973. It is the longest record of a MultiSpectral high-resolution global data set. Many data users find observing change over time one of
the most engaging uses for Landsat data. For example, the GLOBE Program
has developed a new change detection protocol (http://www.globe.gov/tctg/land_prot_changedetect.pdf?sectionId=213)
that asks students around the world to document how the Earth is changing.
Subsetting: Change Detection Images Step 1:
(This step requires the most recent version of MultiSpec©.)
Download all the bands of data for each scene
to be used from the Global Land Cover Facility download web site. Be sure
that the scenes you have selected to be compared
have identical path and row numbers.
Subsetting: Change Detection Images
Step 2: If you plan to use the thermal data, band
61, prepare the data using the procedure outlined in Preparing
the Thermal Band (above).
Subsetting: Change Detection
Images Step 3: Link all the
bands you wish to use from one scene. Subset a study area from this same
scene, following directions under Subsetting Single Images, above.
Subsetting: Change Detection Images Step 4: Open
the B1 or blue band of the second scene and link the bands using the procedure outlined
in Linking Bands of Data (above).
Subsetting: Change Detection Images Step 5:
Once all of the bands are linked in the second scene, pull down the "Window" menu
and select "Show Coordinate View."
Subsetting: Change Detection Images
Step 6: Open the subsetted image and select "Show Coordinate
Subsetting: Change Detection Images Step 7:
In each image select the "Coordinate" pull down menu and select
the Lat-Lon (Decimal) option.
Subsetting: Change Detection Images Step 8: Bring
the subset ted image to the front.
Subsetting: Change Detection Images Step 9:
Pull down the Edit menu and Select All to select the entire image. Go back to the
Edit pull down menu, and select "Selection Rectangle." When the
window pops up, click on the "Units" pull down menu, and
change the units to Latitude-Longitude. Check the box labeled "apply to all image windows. "
Follow the next steps for each image:
Subsetting: Change Detection Images Step 10: Pull down the"Processor" menu,
and highlight "Reformat image." A box will appear; select "Change
Image File Format."
Subsetting: Change Detection Images Step 11:
In the "Image File Format Change Options" window find the "header" pull
down menu, and select GeoTIFF format. (This option will only work if the Landsat data
is originally a GeoTIFF. The GeoTIFF file format is ideal because the file header contains all
of the geographic information.)
Subsetting: Change Detection Images Step 12:
Click "OK". When the next box pops up, don’t change the start and
end lines and columns, but make sure the intervals are set at one. Click OK.
Subsetting: Change Detection Images Step 13: The
next box to pop up is for you to name and save the multi-channeled image. Give the
image a name such as "name of county" and the date the image was taken.
End the file name with the file extension ".tif" An
example would be "Seattle_06_23_01.tif" Make sure you are
saving the image to the same file where you have all the previous images.
Subsetting: Change Detection Images Step 14:
Repeat the steps 10 through 12 for the second image.
Once each image is created, you are ready to study how the area
has changed over time.
To help with this procedure you can use
GLOBE Program's Change Detection protocol
NASA's Grow Smarter website
or the NASA Landsat Change Detection website.
To determine the amount of storage capacity
required by Landsat data, use the following formula: multiple the number of lines by the number of columns
by the number of bands you are using. for example, the GLOBE program's Landsat scenes
are 512 X 512 pixels, and include only the first 5 Landsat bands of data. (This format was selected
partly so that the image file would fit on a floppy disk.) The GLOBE program's Landsat
file is 1.31 MB.(512 lines x 512 columns x 5 bands = 1,310,720 bytes or 1.31 MB) The area a 512 X 512
pixel image covers is 15.36 Km by 15.36 Km. Remember that each pixel is 30 meters by 30 meters.
The largest area that will fit on a floppy disc if
you are using all 7 bands of data is 430 X 430 pixels
The area a 450 X 450 pixel image covers is 13.50 Km
by 13.50 Km. If you want to make an image with a
larger spatial extent be aware that these images will test both
the CPU speed
and RAM memory of your computer. A laptop computer
with 192 RAM and a CPU speed of http://www.nasa.gov/about/highlights/HP_Privacy.html466
loads full Landsat scenes very slowly and MultiSpec© has
difficulty displaying these scenes at full resolution. A full
Landsat scene has approximately 7,000 lines or rows by 8,000
columns of pixel data