Remote Sensing
In this lab, we will explore a multispectral remote sensing image acquired by one of the Landsat satellites. The dataset for this lab is very large, so you will need to be patient with the download and display of the dataset. Begin by downloading the Salt Lake County Landsat Data.kmz file from Canvas.
Once the file has downloaded, the "True Color Composite" of the Landsat scene should be displayed in Google Earth. It is called a true color composite because it uses three bands (blue, green, and red wavelengths) to produce an image that replicates what we might see with our own eyes.
This image was acquired by the Enhanced Thematic Mapper+ (ETM+) sensor on Landsat 7 on May 31, 2001. Zoom in to examine the image more closely. You will notice that the spatial resolution of the image does not dramatically improve when you zoom in - the spatial resolution of this image is 30 meters.
Once you have had a chance to explore the image, create placemarks on each of the following surface types. We will use these placemarks as reference points to understand how each surface reflects or emits electromagnetic radiation at different wavelengths:
1. Green vegetation
2. Soil/brown vegetation
3. Water
4. Snow
5. Salt flat
Make sure you label each placemark so you don't forget what surface it is marking.
Next, turn off the "True Color Composite" layer and turn on the layer labeled "Blue Band". This layer shows only the band that measures the blue portion of the visible spectrum. Once you have looked at each of your placemarks, also examine the "Green Band" and "Red Band" layers.
We can also display bands that are outside of the visible spectrum. When you have finished looking at "Blue Band", "Green Band", and "Red Band", turn on the "Near Infrared Band" layer. This layer contains a band that is slightly longer in wavelength that the visible region of the spectrum. The near infrared is still reflected solar radiation. Again, look at each of your placemarks. Note that green vegetation should be much brighter in this layer than it was in the visible layers.
We can combine multiple bands to create a "False Color Composite". In this example, the near infrared wavelength band is displayed as the color red, the red wavelength band is displayed as the color green, and the green wavelength band is displayed as the color blue. If this confuses you, think of the wavelengths used to create the color image as shifted to longer wavelengths so we can visualize wavelengths we normally can't see.
When you display the "False Color Composite" layer, vegetation should now appear red. This is because vegetation has a high near infrared reflectance, and the near infrared band is being displayed as the color red.
Next, turn on the "Shortwave Infrared Band" layer. This band is still reflected solar radiation, but at an even longer wavelength than the near infrared. Note how the brightness of the image changes at each placemark. Snow should now be much darker than it was in the visible or near infrared.
The "Thermal Infrared Band" layer contains a measurement of emitted radiation. Brighter tones indicate warmer temperatures, and darker tones indicate cooler temperatures. Adding some color to the thermal infrared data will help us interpret the temperatures of different surfaces. Display the "Thermal Infrared Color" layer. In this image, we have made the coolest temperature black or blue and the warmest temperatures orange or red.
Once you have visited each of your placemarks for each data layer, answer the following questions. For question 7, all information should be contained within a KML file. Submit your answers (questions 1-6) and KMZ to Canvas by 1:00 PM, Monday, 25 May.
1. Which of your placemarked surfaces is brightest in the green band? Which surface is darkest?
2. Which surface is brightest in the shortwave infrared band? Which surface is darkest?
3. Which surface is hottest, as indicated by the thermal infrared band? Which surface is coolest?
4. How does the quantity of light reflected by green vegetation change from the visible to the near infrared?
5. How does the quantity of light reflected by snow change from the near infrared to the shortwave infrared?
6. Using the Thermal Infrared Color layer, describe the apparent relationship between temperature and elevation.
7. Create a short tour comprised of the following three placemarks.
a. First placemark will take the viewer to the location you consider to be your hometown. Include:
- Name of town
- 1-2 sentence description
- Range of 2500m
- Heading facing north
- Tilt of 0°
b. Second placemark takes the viewer to a location you traveled to this past year (this must be different than the location you set for 7a).
Include:
- Name of location
- 1-2 sentence description
- Range of your choosing
- Heading facing south
- Tilt of 45°
c. Third placemark takes the viewer to a location you would like to travel to in the future (this must be different than the locations you selected for 7a and 7b).
Include:
- Name of location
- 1-2 sentence description
- Range of 4000m
- Heading facing east
- Tilt of 70°