This midterm is worth a total of 45 points (25% of your total grade). Read the questions carefully and provide specific answers. Please feel free to ask for help if any of the questions confuse you.

All answers must be in complete sentences to receive credit, unless stated otherwise. Do not provide one word, bulleted responses. Please, make an effort to be neat with your answers.

1. What are key factors that determine if remote sensing is the most effective method to map some parameter of an urban area? Specifically, what circumstances would suggest to you that remote sensing is the best approach. (4 points).

A range of answers can be given here – any four of the points below are acceptable. Probably most critical are: (1) the size of the area to be mapped- which in turn relates to the cost savings that result from using remote sensing; (2) the number of times the area would be re-mapped; (3) the frequency of mapping you need (e.g., daily, monthly, annual; (4) the required timing(e.g., passive remote sensing might not work in winter in Eugene); (5) whether the parameter can be “seen” using remote sensing (e.g. subsurface sewers systems probably cannot be mapped remotely); and/or (6) the spatial resolution that is required. . In general terms, the bigger the area to be mapped, the more often it will be mapped, and the larger the spatial resolution, the more sense it makes to use remote sensing

2. What are major components of the remote sensing system around which this class is structured? A list of terms is okay. (3 points)

3. Given that 1 nanometer (nm) = 10^-9 m, 1 micrometer = 10^-6 m and 1 millimeter (mm) = 10^-3 m: a) how many nanometers in a micrometer; and b) how many micrometers units in a mm? (2 points)

4. On the graph below, draw and label the electromagnetic spectrum as it is recorded at the top of the earth’s atmosphere for emissions from the earth and from the sun. Specifically:

a) Draw a curve showing the spectra and intensity of energy emitted by the earth. Label the curve with “Earth.” (1 point)

b) Draw a curve showing the spectra and intensity of energy emitted by the sun. Label the curve with “Sun.” (1 point)

c) On the x axis, label the ranges that constitute: visible light, mid-range IR, ultraviolet light, thermal IR, SWIR radiation, and near IR radiation (3 points)

Visible: 0.4 – 0.7 um

5. Fill in the table below with the colors that the human eye would perceive if you mixed together the following wavelengths of light (3 points):

Colors	Result
Blue +red =	Magenta
Red + yellow =	Green
Blue + green + red =	White
Black + white =	Gray
Green + near infrared =	Green
Near infrared + thermal infrared =	Black

6. Imagine yourself at a computer screen with red, green and blue “guns.” If vegetations reflects strongly in the shortwave IR range and relatively weakly in the red and green range, what dominant color will the vegetation appear to be on the screen if you assign the near IR band to the red gun, the red band to the green gun, and the green band to the blue gun? (1 point)

7. Why is vegetation green to the human eye? Explain in terms of how scattering, absorption, reflection, and/or transmission processes interact with blue, green and red light (2 points).

Because chlorophyll primarily uses (absorbs) blue and red light for photosynthesis and reflects or transmits relatively more green light.

8. Why are bricks on the Oregon campus reddish in hue to the human eye? Explain in terms of how scattering, absorption, reflection, and/or transmission processes affect blue, green and red light (1 points).

Because the bricks primarily absorb relatively more blue and green light and reflect relatively more red light.

9. Imagine you have a paint that seems colorless to the human eye, but absorbs blue light (light a blue camera filter can absorb blue light). How would the color of the Oregon bricks change (if at all) if you painted them with this paint? Explain your answer. (2 points)

The color would not change. Red and green light would still be transmitted through the paint to the bricks. The bricks would absorb the green light and continue to reflect the red, leaving them the same color.

10. , In the shortwave IR wavelengths, why does water appear black relative to other features on the images we have looked at in lab? (1 point)

Because water absorbs almost all incoming SWIR radiation and none is reflected back to the sensor.

11. What are atmospheric windows and why are they so important to climate and life on earth? Discuss both solar and terrestrial emissivity (i.e., radiation emitted by both the sun and earth) (3 pts).

An atmospheric window is a spectral band in which radiation is largely transmitted through the atmosphere without being absorbed or reflected.

Visible light windows: The earth’s atmosphere allows visible light to reach the earth’s surface. This is very important because this is the peak emissivity range of the sun. If this light was reflected or absorbed very high in the atmosphere, the earth would be very cold. Alternatively, if the visible light were absorbed in the troposphere, we would be very hot as all the sun light would be trapped near the earth. Because this is the peak emissivity range of the su

Thermal radiation windows: The earth’s atmosphere also transmits thermal (terrestrial) radiation. If the atmosphere did not allow this energy to escape, the earth’s surface would be much hotter as all the energy would be trapped near the surface.

12. Under what circumstances does Rayleigh scattering occur and what are two steps you could take to avoid having Rayleigh scattering affect your imagery? (3 points).

Rayleigh scattering occurs when short wave lengths of light encounter molecular sized matter. The greatest Rayleigh scattering is in the shortest wavelengths, because the amount of Rayleigh scattering is proportional to 1/(wavelength)⁴. Blue wavelengths, the shortest in the visible spectra, are therefore more affected by Rayleigh scattering than are green or red spectra. Any two of the following are ways to avoid Rayleigh scattering:

- Collect imagery from times when the sun angle is high, which shortens the atmospheric path length that the light travels through

- Use atmospheric correction programs (e.g., ATRIM, ACORN, MODTRAN) or image enhance approaches to mathematically “remove” scatter.

13. What is radiometric resolution? Provide an example by explaining the difference between 6 bit and 8 bit radiometric resolution.. (2 points)

The number of divisions that the range of data is divided into. For example, an image with 6 bit resolution is split into 64 divisions (values from 0 to 63), while the same image with 8 bit radiometric resolution, is split into 256 divisions (Values from 0 to 255).

14. Fill in the table below to indicate the relative merits of along track and cross track sensors. Use the terms in parentheses to describe the characteristic. Assume that the two sensors are at the same elevation on platforms moving at the same velocity and are using focusing devices with the same degree of magnification (5 points).

Characteristic:

Along Track

Cross Track

Area Covered by an Image (larger or smaller?)

Smaller

Larger

Geometric Distortion

(more or less?)

Less

More

Spatial resolution

(pixels cover larger or smaller area?)

Smaller pixel possible

Larger pixel

Spectral Resolution

(narrow or broad?)

More narrow is possible

Broader

Repeat Period of Imagery

(more or less frequent)

Longer

Shorter

15. Put an ‘S’ for Systematic or an ‘N’ for Non-systematic on the list of potential sources for error on remote sensing imagery below (3 points):

16. You have a digital image from a cross track scanner mounted on an airborne platform. The image looks distorted, with the scale varying across the image and features looking vaguely misshapen. What steps would you take to restore the image to give it a consistent scale across the image and improve its appearance? Specifically:

a) What data do you need to restore the image and where might you acquire these data? List at least two sources for these data. (3 points)

Data that are required are ground control points (1 point). GCPs require that you have sites with known coordinates on the ground that you can also find on the image. You could collect these data through use of (any two):

b) How would you apply these data to restore the image to its proper appearance? (2 points).

- The ground control points would be used to georectify the image – i.e., mathematically stretch the distorted image to fit the GCPs, and

- The image must be resampled (e.g,, nearest neighbor, bilinear, cubic convolution) to match pixel values to the new locations