Lab Instructions
Lab 2, due 5:30 pm September 18, 2007
EES5053/ES4093: Remote Sensing, UTSA
Continuing with ENVI
Objective: understanding the basic principle of Remote Sensing and further
familiarize with some basic operations in ENVI such as enhance display, subset/clip
image, statistics tool, and input and output image.
Part I: Questions and Concepts
1. Passive and active remote sensing
2. Explain the two basic remote sensor systems and give an example on how to
calculate the dwell time and calculate them (for example, using pixel size of 30 m,
keeping other variables the same as in the slide)
3. What are the three characters of EMR, and what is their relationship?
4. What’s radiance?
5. Please explain the processes/path and interactions as energy transfer from sun to
earth and back to sun?
6. Use Stefan-Boltzmann Law to calculate the radiation energy emitted from the
Sun, the Earth, and the Mars. Given the average surface temperatures of the Sun,
Earth, and Mars are 6000 K, 300 K, and 210 K, respectively. What’s the energy
fraction of the Earth and Mars compared to the Sun?
7.
Use Wien’s Displacement Law, Given the surface temperatures of the Sun,
Earth, and Mars are 6600 K, 330 K, and 220 K, respectively, to calculate the
wavelength of the peak radiation of Sun, Earth, and Mars. Discuss the wavelength
differences and energy content differences among them using the quantum theory.
Part II: Lab
1. Preparation:
(1). Create a new directory Lab2 under c:\Fall2007-RS\YourName\. Launch
ENVI. The same image used in the Lab1 will be used in this lab. So you do not need to
copy any image. But save your results to the Lab2 directory.
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2. Image Tools
(1). Enhance display: Open the image used in Lab 1 and upload a RGB composite
image band 5 (R) + band 4 (G) + band 3 (B); in the image window, click “Enhance”,
there are six default enhance methods for each of the three windows: image, zoom, and
scroll; these enhancements rescale pixel values of the image to make the image a better
contrast, based on pixel values in the image, zoom, or the scroll, while applying to the
entire scroll image. Before you do any performance, please follow the following steps to
find what those method mean.
To find what those six methods mean, you can find them in the ENVI Help (which is
what I recommend you to do it all the time). From the main ENVI menu, click Help ->
Start ENVI Help. A new ENVI Help window popup. Click the Contents -> ENVI User’s
Guide -> Interactive Displays -> Applying Default (Quick) Stretches. You then should be
able to find what they means.
Questions 1: use your own words to explain each of the 6 methods and use the enhance
for [Image] to help you understand each of the methods.
Questions 2: When we use different enhance display, does it really change the pixel
value of the image? Why do they display different color? (use the Cursor Location/Value
tool to help you answer the question)
Questions 3: Load the same image (543) into two other Display windows. Now, you
have three Display windows of the same image. I want you to use the same enhance tool
to [Image], [Zoom], and [Scroll] and tell what are the differences. (use the Link and
Cursor Location/Value tools to help you answer the question)
In the very end of the Enhance tools, there are two advanced enhance tools you may use:
Histogram Matching and Interactive Stretching. There are both very important tools
and will be lectured in the image processing class (will be offered next spring). If you are
interested in learning them by yourself in this class, you are welcomed to do so.
(2) Subset image: Close two sets of Display window; leave only one for this part. In the
ENVI main menu, Click Basic Tool->Resize Data (Spatial/Spectral) (which means that
you can subset your image spatially and/or spectrally). Select the *.img file in the Input
File window, click Spatial Subset. A new Spatial Subset window popup. You can see
there many different ways to subset your image spatially. It can be based on samples and
lines, an image, a map, a file, or a ROI/EVF. In this exercise, you may just use the tool
based on Image. Click Image, an image window will popup. You can move the red
square to anywhere you want or resize to any size you want. Then click Ok, click Ok.
Now, you can also subset your spectral from 6 bands to 3 bands or 1 band. Click the
Spectral Subset button, you can select any band or bands to subset. In this lab, you may
keep all of them, click Ok and OK. A Resize Data Parameters window popup. In this
window, you can change the pixel size to larger, smaller, or the same. You can also select
different resampling methods: Nearest Neighbor, Bilinear, or Cubic (again, what these
tools means will not be lectured or required in this class but in the image processing
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class. If you are interested in, you may check the ENVI Help or come to ask me). For this
lab, please keep the default parameters or method. To output the results, we have two
ways. 1. Output Results to File, Choose the output path and folder (Lab2 directory, in
this lab), or you can check to Memory (temporary save to there, usually for test or for
temporary results, it will lose after closing the ENVI).
Questions 4: Illustrate your subset image and give the size of the image and the specific
area of the subset image.
(3). Statistic tool: Click Basic Tool-> Statistic-> Compute Statistic, then choose your
input *.img file, keep all default parameters, click ok, Then check basic stats and
Histogram, click Ok. You also can change the parameters and output the statistic results
to file. Please try it by yourself. Also do the statistic for the subset image.
Questions 5: Show and compare the statistics of the original image and the subset image
(plot the histogram and legend of 6 bands in one figure as below). Give your basic
interpretation and understanding of the statistics and differences for the two images.
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