Lab 4

Displaying and Understanding a Digital Image      

Geog 418/518, Fundamentals of Remote Sensing

Name 1                                                       Name 2                                            

Go into the Lab 4 folder and open the Landsat Thematic Mapper image lanier.img from Georgia. 

1. The lanier.img image has seven bands (“layers” in ERDAS) that cover the spectral ranges shown in the table below.  Based on what you have learned in class, label the name of the spectra covered by each band (be as precise as possible, e.g., state “red” rather than “visible”).  Check out the Field Guide if you cannot remember which spectral ranges correspond to different names (You will note that spectral ranges for certain IR band widths differ slightly from what I gave you in class.  This is typical – there is not a single widely accepted definition of the spectral range for these different IR bands.)

2. Fill in the minimum value, the maximum value, and the mode value for each band using the Utility/Layer Info command.

3. Why do the minimum values from band 1 through band 7 (excluding band 6) vary in this way?  Be specific in describing which bands are most affected by certain processes.

4. Why does band 6 not fit this pattern?  Specifically, why is its minimum value higher than those for bands 5 and 7.

5. Considering the entire image, why do all values range between 0 and 255?

6. If you were trying to detect subtle differences in reflectance from the surface, would you rather have higher radiometric resolution (e.g., 10 bit) or lower (e.g. 6 bit) resolution?  Why?

7. How can you tell the image is a raster image rather than a vector image? (There are many possible ways to determine this).

8. In terms of the precision of boundaries and point locations, what differences are there between a raster image and a vector or paper map?  Which is preferable for this purpose?

9. In terms of showing subtle variations in landcover (e.g., variations within a forest), is a raster or a vector image preferable?  Why?

10. What is the size of one pixel on the image?  What are two ways to determine this?

11. What geographic coordinate system is the image projected onto? 

12. What is the 0,0 point (the origin) for the pixels (NOT for the geographic coordinate system) and in what direction do the pixel counts get higher?  For example, does the x file coordinate get higher as one moves up or down the image?  What about the y coordinate value for the pixels?

13. How did you determine your answer for number 12?

14.  Use the software to determine the approximate distance (to the nearest 100 meters) along the major freeway cutting from SW to NE across the image?  How did you determine this?

15. Use the Spectral Profile Tool to fill in the table below.  The numbers refer to the pixel file coordinates. 

16. Using the data above, fill in the graph below, using different colors or symbols for the different lines.  Label each line.  If you wish, you may print out your graph from the Spectral Profile window and attach it with this lab, but be sure to edit the graph so that the different lines are clearly identifiable.

Please answer the following questions with respect to absorption, scattering, and reflection.

17.  Why are the values for water so consistently low?

18.  Why is it that the forest values are relatively low in bands 1, 2 and 3, but abruptly increase in bands 4 and 5?

19.    Why do you think the fields have higher values in all bands than the forest?

20.  Which of the various surfaces is the warmest?  Why is this?

21.  Speculate on the nature of the mystery area based on a comparison of its spectral graph relative to other materials.

22.  How might you use the kind of spectral information you have gathered to find or classify similar features in the rest of the image?