UT GEO 371C - The Desertification of the Gobi Desert and Its Effect on Beijing

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Lauren Welker 12/7/09 The Desertification of the Gobi Desert and Its Effect on Beijing I. Goal Asses the rate of desertification of the Gobi desert, and determine, at its current rate, how long until it spans into Beijing, China’s second largest city. I will do so using data stored in a variety of formats (shapefile, geodatabase feature classes, and raster .sid), obtained from various sources, such as the USGS, Encarta Encyclopedia, and the Nasa Zulu database. II. Problem Even though the Gobi is distant from China’s capital, Beijing, dunes are forming just 70 km from the city, and may be drifting south at 20-25 km a year, with conservative estimates saying 3 km a year. Despite massive spending by the Chinese government on land reclamation and replanting, China cannot keep up with the rapid expansion of the desert. Only 7% of Chinese land is viable farmland, and half of China’s 617 largest cities face water deficits. Beijing is among the cities which will be most affected. By analyzing the obtained data, hopefully I will be able to answer, at its current rate of expansion, how long until the Gobi’s boarders reach Beijing? Furthermore, I can compare my results to current projections to gauge how accurate my approach is. III. Data The Data used from my project was obtained by three sources: 1. The Lab 2: Map Projections and Coordinate Systems file, specifically the world30 file 2. A gif imaga of the Gobi desert from http://images.encarta.msn.com/xrefmedia/aencmed/targets/maps/map/T028749A.gif 3. MrSid files of landsat data from 1990 and 2000 from Nasa Zulu website. IV. Procedure The procedure involves the following general steps: 1. Create Map area of Mongolia and China 2. Geofrenence the gif image of the Gobi desert to a map of China and Mongolia to get an approximation of the perimeter of the Gobi; 3. Digitize a desert area polygon; 4. Mosaic individual .sid files into a single .sid file;5. Calculate the rate of desertification of the southwest corner of the Gobi from 1990 to 2000 by using spatial analysis. A. Create a Map Area of Mongolia and China 1. Open ArcMap and create a new, empty map. 2. Load the Open ArcMap and create a new, empty map. 3. Load the cntry94 feature class from the geodatabase Mapproj.mdb, found in the Lab 2 folder. 4. Use the selection tool to highlight the countries of Mongolia and China 5. Use the clip tool located in ArcToolBox under Coverage Tools, to extract the selected data. Save the new file under Mon_Chin. The result should resemble figure 1 Figure 1- clipped countries from world map B. Georeferencing 1. Load the .gif file of the Gobi desert into ArcMap. Establish the spatial reference of the photo as 2. Open the ”view link table” 3. Use the add control points tool to pick 3-5 points where the .gif image will link up to the map of Mongloia and China. Zoom into the .gif image layer first and pick the first point, then zoominto the Mon_Chin layer and pick the second point lines up with the first point picked on the .gif image. Continue this process until the maps line up appropriately. 4. Save the links in the Project/my_data folder. 5. Rectify the new georeferenced map, using nearest neighbor resampling, and a cell size of 1, in the spatial reference data frame GCS_North_American_1983. Figure 2-Rectified Georefrenced Map C. Create a Personal Geodatabase 1. We will want to create a personal geodatabase to create feature classes in. 2. Within ArcCatalof, browse to the project folder, right-click on the folder, select “New”, then Personal Geodatabase. 3. Name the new Geodatabase “Gobiproj.mdb” D. Create a Feature Dataset 1. Within ArcCatalog, browse to the project folder, right-click on the Gobiproj geodatabase, select “New”, then “Feature Dataset”. 2. Name the new Feature Dataset “Gobi” and click the “next” button to bring up the Spatial Reference Properties window. 3. Because we will be mainly working in UTM 49N, Browse to Projected Coordinate System>UTM>WGS_1984> WGS_1984 UTM 49N.prj and select, then click “Next”. 4. Accept all defaults and click “Finish”E. Create Feature Classes within the Feature Dataset 1. Right-click on the Geology Feature Dataset, select “new”, then “Feature Class” 2. Name the feature class “Desert_Area”, then select polygon features from the drop down menu for the type; select “Next” The window should resemble figure 2 below Figure 3- Feature Class Set-up 3. Except all defaults and click “Finish”. F. Digitizing the Desert_Area Polygon 1. Open ArcMap and load the rectified Mon_Chin map and the new feature class that was just created. 2. Open the editing toolbar a. From the editing toolbar menu, click “Start Editing” b. On the toolbar set Target to the file you will digitize to (Desert_Area) c. On the toolbar, Choose task- “Create New Feature” d. Select Tool-Pencil e. Begin outlining the perimeter of the Gobi desert featured on the map . f. Once you have fully outlined the perimeter of the Gobi, finish the feature outline with a double click. The selected polygon is featured in figure 4.Figure 4-Saving the edits made for the newly created polygon g. Click “Save Edits” on the editor toolbar h. Click “Stop Editing” on the editor toolbar i. Change the symbology of the polygon to “No Fill”, with a bright red outline 1 point wide. G. Using Satellite Images to Determine How Far the Gobi has Expanded in the Southeast corner, during 1990-2000. 1. Upload the 6 MrSid files obtained from the Nasa Zulu website into ArcMap. 2. Set the spatial reference for each of the files by going into ArcToolBox, Data Management Tools, Projections and Transformations, Raster, and then click on Define Projection. 3. Set the Spatial Reference according to the UTM zone the data is located in. WGS_1984_UTM 49N for the data located in UTM Zone 49N, and WGS_1984_UTM 50N for the data located in UTM Zone 50N. 4. Check the boxes so only the 3 MrSid files containing the satellite images from 1990, and the gobi desert outline is displayed, like in figure 5.Figure 5- Gobi Desert Perimeter Outline and 1990 Satellite Images 5. The edge of Gobi Desert Outline doesn’t quite match up with outline of the desert seen in the satellite images. This is ok! The first outline was just to give us a rough idea of the desert’s location, now we can edit the polygon in the Southeast corner to match up with the desert


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UT GEO 371C - The Desertification of the Gobi Desert and Its Effect on Beijing

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