Lab 2 - Due 7 PM on Sept 13, 2011
Geo5053/4093 - Remote Sensing, UTSA
http://www.utsa.edu/LRSG/
Student name: _______________
Page 1 of 3
Get Starting with ENVI
Objective: Understand several basic concepts and get started with professional software
for image processing: ENVI
A. Explain these basic concepts
(1) Remote Sensing
(2) Sun-synchronous satellite
(3) Geostationary satellite
(4) Spatial resolution and coverage
(5) Spectral resolution and coverage
(6) Radiometric resolution and coverage
(7) Temporal resolution and coverage
(8) FOV and IFOV
B. Lab Preparation
(1) Create your own sub-folder C:\UserData_ENVI\yourname\
For example, C:\UserData_ENVI\Xie\
(2) Go to the LRSG server (\\129.115.25.240\XIE_misc\Fall08-RS\) and copy the Lab2
folder into your sub-folder. [The server is accessible only from the UTSA lab computers].
Control-click the link above, or copy-paste it into the Windows Explorer address bar and hit
Enter. You will see the Lab2 folder. Drag-and-drop or copy-paste Lab2 to your sub-folder.
(3) Open your copy of the Lab2 folder and look for two files, which are a subset of
LandSat ETM+ image from path27, row 40, acquired on July 21, 2001.
Header file: ETMp27r40y01m7d21.hdr, storing the coordinate and projection
information as a 1 KB text file.
Image file: ETMp27r40y01m7d21.img, storing all of the digital numbers and image
bands as a 22 MB data file.
Lab 2 - Due 7 PM on Sept 13, 2011
Geo5053/4093 - Remote Sensing, UTSA
http://www.utsa.edu/LRSG/
Student name: _______________
Page 2 of 3
C. Starting with ENVI
ENVI is professional image processing software commonly used for image processing and
analysis by remote sensing scientists. In this class, you will use the "ENVI 4.8" and "ENVI
online manuals and tutorials", which are great materials for you to learn how to use the ENVI
package. ENVI is very powerful and user-friendly software. We cannot practice all of its
functions in class, so you are encouraged to explore them yourself with the help of tutorials.
(1) To start ENVI, select Windows Start -> All Programs -> ENVI 4.8 -> ENVI, or
you can try to create an ENVI 4.8 icon on your desktop. The ENVI + IDL 4.8 icon also works,
but it uses unnecessary computer resources (IDL is the ENVI programming language, and is not
covered in this class). Select ENVI toolbar -> File menu -> Open Image File, which opens the
Enter Data Filenames window. The default data directory (C:\Program Files\ITT\IDL\IDL80\
products\envi48\data) contains some datasets for you to freely use, however you must be careful
to never store any lab results in this location. Navigate to your subfolder (i.e.
C:\UserData_ENVI\Xie) and choose ETMp27r40y01m7d2.img. This opens the Available
Bands List window that lets you select specific Landsat ETM+ bands to view. Note the decimal
numbers at the far right of each band name (i.e. 0.4850), which corresponds to that band's center
wavelength in micrometers. For ETM+ image, Band 1 represents blue wavelengths, Band 2 is
green, Band 3 is red, and Bands 4, 5 and 7 are near infrared. Note Band 6 is a thermal band
(10.4-12.5 micrometers), which is not included in the dataset for this lab.
(2) You can view the image in Gray Scale (single band mode) or RGB Color (three
band mode). For a gray scale example, click on Band 3, then the Load Band button at the
bottom of the Available Bands List window. For a color example, sequentially click on Band 5,
Band 4, then Band 3, then the Load RGB button. This opens an image of San Antonio, and
displays it using 3 windows.
(3) Please get familiar with these 3 windows (Image, Scroll, and Zoom). Try to find
Loop 410, Loop 1604, the UTSA main campus, downtown San Antonio, and other places you
are interested in and familiar with.
Question 1: What are the main differences of the 3 windows?
Questions 2: Illustrate and mark three or more targets you find in the image. You might use the
ENVI toolbar -> Basic Tools menu -> Measurement Tool to measure the extent or area of
each target. Use Alt + PrintScrn to copy/paste snapshots of these targets into your lab report.
(4) You can open the same image using multiple sets of bands. First: on the Available
Bands List window, select the RGB Color option, sequentially click on Band 5, Band 4, then
Band 3, then Load RGB onto Display #1. Next: on the Available Bands List window, click the
Display drop-down menu (at the bottom) and select New Display. Then select RGB Color
again, but this time sequentially click on Band 3, Band 2, then Band 1, then the Load RGB
button for Display #2. This will display another type of color image, which is not so colorful
compared with the first image.
Lab 2 - Due 7 PM on Sept 13, 2011
Geo5053/4093 - Remote Sensing, UTSA
http://www.utsa.edu/LRSG/
Student name: _______________
Page 3 of 3
Available Band List window
(5) You can link these two sets of display windows for comparison. On one of the Image
windows, select the ENVI toolbar -> Tools menu -> Link -> Link Displays, and click OK.
Now when you click on one display window, the image bands from the other display are
overlaid. Also when you move any of the red navigation squares, both sets of display windows
move together. This is a powerful tool to view the same image using different sets of bands.
(6) There is another powerful tool to see the image data values. Select the Image
Display toolbar -> Tools menu -> Cursor Location/Value. A small popup window gives you
the location (x, y in pixels), screen values, projection, coordinates in meters and
latitude/longitude, and band data values for the pixel that the cursor is pointing to. If you have
two display windows linked, the popup window shows this information for the same pixel of
both displays.
Question 3: Compare the two composite images (RGB bands 5-4-3 and RGB bands 3-2-1),
based on what you have learned so far about remote sensing. Use the tools covered above and
any other tools you may find useful. Give some general interpretation, what you found, what are
the differences, the reasons for the differences, and anything else you can see or think about. I
do not have a standard answer for this question. Anything you can see or give a reasonable
explanation, it is fine with me.