Study Guide for 1st Midterm Exam
BOT/GEOG 4111/5111
Fall 2015
The exam will be short answer and problem solving. Bring a calculator! If you
understand how to answer the questions in this study guide you will be in good shape
for the exam. I will give you the values of any necessary constants, etc. (except the
speed of light!), so you don’t need to memorize them. The exam will include material
covered through the end of the lecture on resolution. Any topics on this review sheet
that we do not cover by then will not be on the exam.
The first midterm exam is on October 6!
Remote Sensing History
1. What is a “camera obscura” and how does it work? Why are the images in a
camera obscura upside down?
2. What were some of the problems that early aerial photographers had to deal
with when photographing from airplanes? How were some of these problems
solved?
3. What innovation by Eastman Kodak was crucial in the development of aerial
photography, and why was it important?
4. What were some early platforms used to carry cameras aloft, and what were
some associated problems?
5. What was one major contribution to civilian remote sensing of Robert Colwell in
the 1950s (see textbook)?
Electromagnetic Radiation – Basic Physics
1. Understand the relationship between the wavelength, frequency, and energy of
electromagnetic radiation. Be able to calculate frequency and energy if you
know wavelength and vice versa. (c = νλ and Q=hv). Be careful with your units,
and be able to convert between them! I will give you the values of any constants
(e.g., Planck’s constant, h) that are used in equations. Be aware that some
values may be expressed in scientific notation (e.g., c = 2.98 x 108 m/sec) and be
able to deal with that. You must know the speed of light in m/s.
2. Be able to draw a diagram showing the main regions of the electromagnetic
spectrum. Label each region with their common names (e.g. visible, near
infrared, gamma, radio, etc.). You do not have to know specific wavelengths, but
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you do need to know which end is the short wavelength end of the spectrum vs.
the longer wavelength end, and you need to be able to put the common names
of the regions in the right order.
3. Be able to name the 3 additive primary colors and the colors that result when
they are mixed in equal proportions (the colored circle diagram).
4. Understand why color theory is important for image interpretation and how to
assign colors to bands to make features display in particular colors (e.g., how
would you display an image to make vegetation look red?; blue?).
5. What is the relationship between the temperature of an object and the amount
of energy it emits? Know the equation that describes this. What is the peak
wavelength emitted by an object of know temperature? Know this equation.
6. Be able to define the terms irradiance, reflectance, transmittance, and radiance.
Know the equations for irradiance and reflectance at the earth’s surface, and
radiance at the satellite.
7. Why is it important to distinguish between reflectance and radiance in remote
sensing? Do satellites measure reflectance? What do you have to know to
convert satellite radiance to reflectance?
8. Be able to describe the three models of remote sensing described in your
textbook. Which have we been discussing to date?
Reflectance Spectra
1. What is a spectral reflectance curve?
2. What is the difference between reflecting light and emitting light?
3. What is the difference between specular and diffuse reflectance? Which is
necessary for most remote sensing to be possible?
4. What does BRDF mean? Why might it be important in some applications (see
textbook)?
5. Be able to draw typical spectral reflectance curves for green vegetation, soil, and
water and to label the x-axis appropriately with the wavelength region
corresponding to each part of the curves (e.g. blue, green, red, NIR, etc.).
6. What properties of plants control the shape of different parts of the vegetation
spectral curve in the visible, NIR, and mid-IR?
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7. Show how changing leaf water content can affect the shape of the spectral curve
for vegetation.
8. Be able to define and draw the “red edge.” Why is the red edge important?
9. Be able to draw the effect on the spectral reflectance curve for green vegetation
as you increase the number of layers of leaves. Is this change linear or nonlinear? Why?
Digital Data
1. What is a pixel? What is a digital number (DN)? How many DNs are there for
each pixel in an image?
2. What is a satellite “band” (also sometimes called a “channel”)?
3. What is the difference between BIP, BIL and BSQ schemes for storing image data
in files? What is a header?
4. What is a histogram? Be able to draw a hypothetical histogram and to label the
x and y axes. What determines the scale (range of numbers) on the x axis?
5. What is the difference between image coordinates and “real world” coordinates
(like latitude/longitude), and why is it important to assign the latter to images?
6. Why is contrast stretching a useful procedure? Why is it often applied
temporarily rather than permanently?
7. Be able to explain how density slicing works and why it might be useful (see
textbook).
Image Resolution
1. Be able to name and define the 4 types of resolution used to describe remotely
sensed data.
2. Understand the trade-offs for each type of resolution and among different types
of resolution (e.g., why do we often need bigger pixels to have narrower
bands?).
3. What is a mixed pixel? How does the spatial resolution affect the likelihood of
having mixed pixels in an image? (See textbook)
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4. Given several satellite bands, be able to draw a vegetation spectral curve based
only on those bands.
5. Why is the signal to noise ratio (S/N) important in the context of resolution?
Understand the relationship between S/N and a) pixel size and b) the width of
the spectral bands.
6. Define a polar orbit, a sun synchronous orbit, and a geosynchronous orbit.
Explain why one might choose each.
7. What is return time (temporal resolution)? Why might this be important for
tropical remote sensing?
8. What is a panchromatic band and why do they often have higher spatial
resolution than individual red, green or blue bands?
Earth Observing Satellites
1. Using your “cheatsheet” from the October 1 in-class activity, be able to choose
an appropriate satellite for a particular application (e.g., examining global
change in sea ice extent; measuring the effect of drought on Laramie Basin
plants)
NOTE: Any of the above material not covered in lecture by the end of class on
October 1 will NOT be on the exam.
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