RSCC Volume 1
Introduction to Photo Interpretation and Photogrammetry


Table of Contents
Module 1
Module 2
Module 3.1
Module 3.2
Module 4
Module 5
Module 6
Module 7
Module 8
Labs

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These materials may be used for study, research, and education, but please credit the author and the project (Remote Sensing Core Curriculum). All commercial rights reserved. Copyright 1998.

Lab  #3 - Reflectance, Energy Interactions & Earth Surface Features

The purpose of this exercise is to gain an awareness of several fundamental aspects of reflected radiation and spectral response patterns for different features, e.g. vegetation, soil and water. Although satellite images of this type, with the different ranges of the spectrum separated, are different than aerial photography, which combines all the colors, knowledge of how different surfaces reflect in certain wavelength regions is important for air photo interpretation.

In this exercise, it is assumed that filters are used to effectively block out all available energy except the wavelength regions given, i.e. the "blue band" is only the reflected blue light, the "red band" is only the reflected red light etc. 

The idea here is to familiarize yourself with which wavelengths maximize class separability, knowledge of this may be able to help you choose the proper film and/or filter combinations for a given aerial photographic application.

Band 1 (0.45 to 0.515um, 30m), Band 2 (0.525 to 0.605um, 30m, Band 3 (0.63 to .69um, 30m),
Band 4 (0.75 to .90, 30m), Band 5 (1.55 to 1.75um, 30m), Band 6 (10.40 to 12.5um, 60m), 
Band 7 (2.09 to 2.35um, 30m), Band Pan (0.52 to 0.90um, 15m)

More information, and images, available on this page
(http://www.geog.ucsb.edu/~jeff/115a/remote_sensing/landsat7/landsat7bandspalmsprings.html)

In principle, the higher the reflectance contrast between two objects, the easier it should be to distinguish between them. The Santa Barbara satellite image that will be used for this exercise was acquired in September of 1999 by the Landsat Enhanced Thematic Mapper (ETM) Instrument.  The multispectral image characteristics are broken apart into six different wavelength images, one for each band of wavelengths.

 

Band 1 = 0.45-0.52 (blue)

Band 2 = 0.52-0.60 (green)

Band 3 = 0.63-0.69 (red)

Band 4 = 0.76-0.90 (near-infrared)

Band 5 = 1.55-1.75 (mid-infrared)

Band 7 = 2.08-2.35 (mid-infrared)
Composite images are created by putting three bands together. See additive color for a visual explanation of how the  different bands combine, the "natural color composite" is called that because it is supposed to mimic how it would look naturally to your eyes (and how it looks in natural color photography), the "false color composite" is supposed to mimic color infrared photography (healthy vegetation is red, like color infared photographs).

bands 3,2,1
(natural color composite)

bands 4,3,2 
(false color composite)
Questions

1. In the band 4 image the water (i.e. the slough) is easy to distinguish compared to the band 1 image.  Why?

2. Can you determine from the shadows in this image, whether it was taken in the morning or the afternoon?  How can you tell?  Were some wavelengths more informative than others?  Which ones? 

3. Find the airport runways.  In some of the images the runways are darker than the surrounding ground and vegetation.  In some images the reverse is true.  Still in others, the runways are difficult to identify.  Why is this so?

4. Identify some thing whose reflectance, as a function of wavelength, is similar to the runway. Compare their appearance on the image with that of the runway.  Explain why they are similar?

5. Identify the following features using those bands in which they are most discernible:  grass (golf course), water (slough), sand (beach), and cement (runway).  Plot and connect each features' spectral signature (high-white, medium-gray, low-black) on the four graphs provided below.

6. Combine the individual curves on the final Combined Spectral Plots graph in a decipherable manner using colored pencils or different line symbols, provide a legend identify which lines correspond with which surfaces.

7. From the results obtained in #6, determine the bands of the electromagnetic spectrum which allow the optimum discrimination of any one target from another.  Record your answers in Table 4, in the white boxes label which bands are best for telling the difference between the two classes, i.e. which band(s) show the best seperability between cement and grass, between water and cement etc.

8. Select the bands which are optimum for discriminating among the three general classes of vegetation, water, and sand/cement. Record your answers in Table 5.  Discuss the rationale for your decision; why were these the best bands? (feel free to use the class webpage or your text book)

9. Why is it important to investigate the nature of wavelength reflectance from targets when planning aerial photography missions?


 
 

 
 
Table 4. After you have plotted the combined spectral signatures, use that the graphs to decided which band of wavelengths separate cement vs. grass, water vs. grass, water vs. cement etc. Fill in the white box with the band number or the name of the wavelength region (blue, green, red, infrared etc.) 

Table 5. Using the same reasoning, decide which band of wavelengths are best for interpreting between these three broad types of surfaces. (which band is best for separating water and vegetation? etc.)

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