ARSET EO4IM Webinar Session 2 Homework
The purpose of this exercise is to expand on the Landsat Explorer Application demonstration from Session 2 of the EO4IM Webinar. This service is a great method for visualizing the concepts explored in the webinar. It is also useful for quickly examining and analyzing remote sensing data. The completion of this homework fulfills the Homework 2 requirement for the certificate of completion. For credit, you only need to complete the required questions (marked by the red asterisk). Correct answers are not required for completion credit; the intention of the exercise is to encourage participants to become familiar with the application. If finishing this assignment is not possible, you can reach out to eo4imarset@gmail.com. Please complete this homework by the beginning of next week’s webinar session.
Name of participant *
Your answer
Email address of participant *
Your answer
***Correct answers are not required for credit; the intention of the exercise is to encourage participants to become familiar with the application. Answers can be viewed at the end for personal grading and comparison. This exercise will only be marked for completion.***
Your answer
1. This homework will be an extension of the Landsat Explorer application demonstration from the Webinar. To begin, visit the Landsat Explorer application at http://landsatexplorer.esri.com/. For additional help using the application, click the “App Tutorial” button (seen below) along the sidebar.
2. Using the search bar in Landsat Explorer, navigate to Porto Velho, Rondônia, Brazil.
3. Porto Velho is the capital city of Rondônia, Brazil, one of the most deforested areas of the Amazon. Imagery of this region is interesting because it will show a wide variety of landscapes, including urban, agriculture, forest, and rivers. You can also see shrinking forests and expanding urban and agricultural areas when you look at a time series or perform a change detection. All these phenomena will be examined during this exercise.
Your answer
4. Use the Render icon (seen below) to choose difference band combinations.
5. Examine urban expansion and agricultural activities in deforested areas.
a. Which rendering shows what a human would see from space? *
Your answer
b. What color is vegetation using "Color Infrared”? *
Your answer
c. What color is vegetation using “Short-wave Infrared”? *
Your answer
d. Choose the rendering that best distinguishes vegetation from water and bare soil. *
Your answer
6. Click on the “Identify” icon (seen below) on the toolbar.
7. Select a point of interest on the current imagery around Porto Velho. This will show a spectral profile graph (as discussed in the webinar) of that point, providing the spectral value of the point in each of the eight Landsat 8 bands. You can turn on and off various typical spectral profiles for comparison. Examine which typical profile your point most closely resembles. Click a few other points to view their spectral profiles.
8. Click the “Mask” icon (seen below) to open the Mask window. The default index presented is the Normalized Difference Vegetation Index (NDVI), a measurement of the difference between the near-infrared and red bands. Vegetation strongly absorbs red light and strongly reflects near-infrared light, so healthy vegetation will register higher NDVI values in the -1 to 1 scale.
9. The mask feature displays, visually and numerically, the amount of vegetation in the region by highlighting, or masking, regions with user defined NDVI values. You can also view a specific area by checking the box next to “Define Area of Interest” and drawing a shape over the imagery. This allows you to view important areas that you want to study.
10. Experiment by adjusting the range of values on the “Mask” slider.
Your answer
a. What is the range of values for the vegetation index (NDVI)? *
Your answer
b. What does setting the mask value to 1 do? Then 0.8? How about 0? *
Your answer
c. What NDVI value range do you think represents forests? *
Your answer
11. Using the dropdown menu in the Mask box, select other indices to view, such as the Soil Adjusted Vegetation Index or the Urban Index.
Your answer
12. Ensure that you are still viewing Porto Velho, Rondônia, Brazil. If necessary, enter the city in the search bar to find it.
Your answer
13. While zoomed into the Porto Velho, click the “Time Selector” icon (seen below).
14. Choose the calendar icon (seen below) to show the dates in a drop down list.
15. Select the date July 24, 2018 (a cloudless image). (Different locations have imagery taken at different times. If these dates do not appear in your “Time Selector”, make sure to navigate to Porto Velho. These dates are available when viewing the city.)
16. Click a point on the map around Porto Velho to view a temporal graph of that location. You can view multiple indices at once by checking the boxes next to NDMI Moisture, Urban, and NDVI Vegetation at the bottom of the graph. This graph shows how these various indices change over time at that point.
a. What does this graph say about this location? Is it predominantly forest, agriculture, urban or other? *
Your answer
b. How does it change seasonally and over time? What could account for these changes? *
Your answer
17. Exit out of the temporal graph by minimizing the window.
Your answer
18. Ensure that you are zoomed in on Porto Velho, Rondônia, Brazil. Click the “Time Selector” icon again. Choose the calendar icon ("Show dates in drop down list") to select the date 1/8/2001 and select “Set Current as Secondary Layer” (downwards arrow at the top right corner of the window seen below). Then choose the scene from 24/7/2018 for a comparison date. (Different locations have imagery taken at different times. If these dates do not appear in your “Time Selector”, make sure to navigate to Porto Velho. These dates are available when viewing the city.)
19. Choose the swipe icon (seen below) to compare the two images side by side. Move the swipe window to the left and right to view differences. Think about what changes you see.
20. Click the change detection icon (seen below) to view the results.
21. If done correctly, the "Change Detection" window seen below should appear. Just as in the Mask function, you can define an area of interest to focus on specific regions.
22. The default index used in this change detection is a vegetation index, and the default mode for this change detection is a Difference Image, which shows how features have changed through time. Play with the transparency slider to view the satellite imagery under the difference image.
Your answer
a. What do the areas that are green and magenta represent in the landscape? *
Your answer
23. Experiment with changing the index; try the Urban Index to see how much Porto Velho has grown.
Your answer
24. Click the “Mode” dropdown and select “Difference Mask”. This mode functions similarly to the mask that we used before, although instead of masking current NDVI values, this time you are masking pixels based on the change in their NDVI between the two dates. When the user specifies a range, the regions that have experienced the NDVI change on the upper and lower ends of the distribution are highlighted in green and magenta. This allows for the examination of the most extreme change between the two dates.
a. What do the different colors using the urban index indicate about changes in the landscape? *
Your answer
25. Set both positive and negative vegetation index sliders to values of your choosing. This allows you to visualize, measure, and understand the change that has happened in the region.
Your answer
a. At the ranges you selected, how many square kilometers of change are there in the positive and negative direction? *
Your answer
b. What do you think change in the negative direction shows? *
Your answer
***One important point to note is that this method of change detection is very cursory. Without validation, this map is not necessarily a very accurate portrayal of the change over the years. This method can be very useful for a rapid assessment to get a general idea of landscape trends and to indicate locations of potential ecosystem threats for further investigation.***
Your answer
Bonus Steps
1. Click the “Add Data from ArcGIS Online” icon (seen below). When you are prompted to sign in to your account, just click the X in the top right corner. In this pop-up window, you can search for additional data layers on the internet. If you click the “File” tab, you can also select data, such as GPS points or a shapefile, from your computer. Boundary shapefiles could be used to draw an area of interest in both the Mask and Change Detection functions.
2. Click on the “Stories” icon (seen below) on the toolbar. The pop-up window contains multiple different stories created using the Landsat Explorer. These stories show the power and potential of this tool in earth observation and land monitoring. Look through any stories that interest you. Use the arrows at the top and bottom of the left panel to move between pages of the story.
Submit
Never submit passwords through Google Forms.
This content is neither created nor endorsed by Google. Report Abuse - Terms of Service - Privacy Policy