Page 1 of 16 Appendix 2.3 Terrain Analysis with USGS DEMs OBJECTIVES The objectives of this exercise are to teach readers to: Calculate terrain attributes and create hillshade maps and contour maps. use, automate, and create high quality maps with ArcGIS REQUIREMENTS To complete this exercise, the readers must have the following: Microsoft Windows -based system with a web browser and ArcGIS Desktop 10.1 Advanced (with the latest service pack); and completed the step-by-step exercises in Appendix 2.1 and 2.2 (from this book) so that they will have 1) the USGS DEM data required to complete this exercise, and 2) a beginners level knowledge of the ArcGIS Desktop applications (i.e., ArcMap, ArcCatalog, and ModelBuilder ). INSTRUCTIONS Carefully follow each step below. Refer to the book chapter (Mueller et al., 2014) for background information and context. Installing TauDEM Go to the Taudem website (http://hydrology.usu.edu/taudem/). Click on Downloads. Click on the TauDEM 5.1.2 Self extracting zip file install package or latest version. Install this software on your computer. Open and Configure ArcMap, create a Geodatabase, Adjust Map settings, and Create a Model Open ArcMap. Click Cancel at the Getting Started window to close it. The ArcMap Spatial Analyst extension should still be enabled. If not, refer to Appendix 2.2 for instructions to activate it. Click on View on the main menu and then click Data View. On the main menu of ArcGIS, go to File, Map Document Properties click in the box next to Store relative pathnames to data source and click OK. Save the map by clicking File on the top menu and then click Save As. Navigate to the C:\GIS4Cons\Chap02 folder, and enter Terrain as the file name. Click Save. If Catalog and Search boxes are not visible on the right side of your window, click on the Catalog (Figure 2.3.1, Arrow a) and Search (Arrow b) on the main menu to turn them on. Click on the Catalog tab in the lower right (Arrow c). Save your map document (on the main menu, click on File and Save). Create a Model and Add and Project Elevation Data Catalog should have a split window as shown in the figure. If it does not, click on the Toggle Contents Window button (Arrow d) until you see the split windows. In Catalog, navigate to C:\GIS4Cons\Chap02, click on the Chap02.tbx (you will see the existing tools open),
Page 2 of 16 right click on the Chap02.tbx toolbox, and chose New and then Model. A ModelBuilder window will open named Model. Close the ModelBuilder window. In the toolbox right click on Model, click Rename, and type the new name TerrainAttributes. Right click on the TerrainAttributes model and select Edit. In the menu of ModelBuilder, click Model and then Model Properties. Next, click on the Environments tab, scroll down and click on the check box next to workspace. Click the Values button. Click on the word Workspace. Click on the yellow folders and set both the current and scratch workspace to C:\GIS4Cons\Chap02\Results. Click OK twice to close the windows. Figure 2.3.1. Adding elevation data to the terrain analysis model. In the Catalog (on the right side of your ArcMap window), navigate to the DEM directory and click to open it. There is a subdirectory within the DEM directory. Drag the elevation data (Fig. 2.3.1, Arrow e) from the Catalog tab and move it to the model (Arrow f). Your file name will be different than ours and your file might have a.tif extension. You will need to transform the coordinates of your elevation data because they are in geographic coordinates (i.e., latitude and longitude). Since you will be calculating slope gradient, the coordinates must have units of distance (e.g., feet, meters) rather than angles (e.g., decimal degrees). First examine the properties of the data as you downloaded your DEM from the National Map. Right click on the elevation DEM in ArcCatalog (Fig 2.3.1, Arrow e) and chose Properties. A Raster Dataset Properties pop-up box (Arrow g) will appear. Read through this information box and write down the following information about your NAIP imagery: number of bands, cell size, spatial reference, and angular units. In our case, we had 1 band, a 9.2592593e- 005, 9.2592593e-005 cell size, a GCS_North_American_1983 spatial reference, and angular units of degrees. In other words, the raster was a 1-band DEM with angular geographic coordinates that used the North American Datum of 1983 (NAD1983). Click OK to close the dialog box.
Page 3 of 16 Determine and Change the Spatial Reference of Elevation Data Click on the search tab (Fig 2.3.2, Arrow a) and search for the words Project Raster (Arrow b). While holding your shift key down, click and hold on the Project Raster (Data Management) text (Arrow c) and drag it to the model (Arrow d). Click on the text Transforms the raster dataset from one proj (Arrow e) and a popup box will appear with a description of the tool (Arrow f). After a cursory examination of this information, click on the close button (Arrow g) to close this box. Hover your mouse over the text toolboxes\system toolboxes\data managem (Arrow h) and you will see the full text is toolboxes\system toolboxes\data management.tbs\projections and Transformations\raster\project raster. This information is the name and location of the tool within Arc Toolbox. Figure 2.3.2. Examining Tools in ArcCatalog.
Page 4 of 16 Click on the toolbox icon (Fig 2.3.3, Arrow a) to add ArcToolbox to the right hand side of your screen as shown in (Arrow b). Recall the name and location of the Project Raster Tool from the previous step (i.e., toolboxes\system toolboxes\data management.tbs\projections and Transformations\raster\project raster ). The text data management.tbs refers to the Data Management toolbox (Arrow c) which is a file on your hard drive in the directory c:\program files (x86)\arcgis\desktop10.1\arctoolbox\toolboxes. Within that file, there are tool sets which contain either tools or more tools sets. The Project Raster tool (Arrow d) is a tool from the Raster toolset (Arrow e) located in the Projections and Transformation toolset (Arrow f) which is located in the Data Management toolbox (Arrow c). Explore the toolbox to learn about other tools are available. Expand the size of your model by grabbing the right side (Arrow g) with your mouse and dragging it to the right. Observe that you can find ArcToolbox from now on by clicking on the toolbox tab at the bottom of the right hand side window (Arrow h). Recall that you can go back and forth between windows on the right side of your screen. For example, click on the search window (Arrow i). Save your model. Figure 2.3.3. Exploring ArcToolBox.
Page 5 of 16 Use the Connect tool (Fig 2.3.4, Arrow a) to connect the DEM (Arrow b) to the Project Raster tool (Arrow c). Select Input Raster when prompted. Click on the select tool (Arrow d) and double click on the Project Raster tool (Arrow c). When the project raster popup box appears (Arrow e), delete the contents of the Output Raster Dataset Field and type in the name USGS_DEM.tif (Arrow f). Click on your keyboard tab key and a path to your results directory will appear. To the right of the Output Coordinate System field (Arrow g), click on the icon to change your settings (Arrow h). In the Spatial Reference Properties box, double click on Projected Coordinate Systems, then UTM, and double click on the spatial reference file that represents the same coordinate system that your NAIP was downloaded in as determined in Appendix A.2.2. For our example, the spatial reference of our NAIP data was UTM zone 16 with the NAD 1983 datum. In our case we clicked on NAD1983UTM Zone 16N because we were in Zone 16 (Arrow i). Since the input and output datums are the same, you do not need to enter a geographic transformation. Set the Resampling Technique to BILINEAR (Arrow j) for bilinear interpolation. Interpolation is necessary because the geographic and UTM coordinates do not line up on the same grid. Use the default output cell size (Arrow k). In our case, it was about 9.261174 (close to 30 ft), approximately the original scale of the DEM. Click OK to close the projection windows. Save your model. Click on run (Arrow l). Save your model again. Save your ArcMap Document. Figure 2.3.4. Projecting elevation data in ModelBuilder. Extract and Fill DEM and Calculate Flow Direction and Flow Accumulation In your model move the green USGS_DEM.tif output circle to just below the Project Raster Tool (Fig. 2.3.5, Arrow a). Because the geographic extent of your DEM will be very large, it could cause your computer to crash unless you have a system with sufficient power. To resolve this problem, you will clip out your DEM to the extent of your NAIP imagery. Go to ArcToolbox, and contract the Data Management Tools Toolbox by clicking on the minus sign if it is still expanded. Click on the plus sign next to the Spatial
Page 6 of 16 Analyst Toolbox to expand it, and then open the Extraction toolset. Drag the Extract by Mask tool (Arrow b) to your model below the USGS_DEM.tif output (Arrow c). Now click on the Catalog Tab (Arrow d) and navigate to Results. Grab the NAIP raster and move it to your model to the left of the Extract by Mask Tool (Arrow e). Click on the Connect tool and connect the USGS_DEM.tif to the Extract by Mask Tool (set as Input Raster). Then connect your NAIP imagery from the previous exercise to the Extract by Mask Tool (set as Input Raster or Feature Mask Data). Select the Extract by Mask Tool and change the output raster name to DEM_ext.tif. Then move DEM_ext.tif to just below the Extract by Mask Tool. Save your model. Click on Run (Arrow f). You should see a shadow on your green output circles indicating the layers have been created. Save your model again. Figure 2.3.5. Extracting a sub area from the USGS DEM. Next we will add the TauDEM Toolbox to ArcToolbox. Scroll to the top of the ArcToolbox, right click on ArcToolbox (Fig. 2.3.6, Arrow a), click on Add Toolbox. Browse to the TauDEM install directory (C:\Program Files\TauDEM\TauDEM5Arc), click on the TauDEM_Tools.tbx file, and click Open. You will see a TauDEM toolbox in your ArcToolbox (Arrow b). Open the Basic Grid Analysis Toolset (Arrow c). Grab and drag Pit Remove (Arrow d), D-Infinity Flow Directions (Arrow e), and D-Infinity Contributing Area (Arrow f) into your model, placing them at the locations indicated by Arrows g, h, and i in Figure 2.3.6. Be sure to relocate the green output data sets as shown in the figure. Connect DEM_ext.tif to Pit Remove (set as Input Elevation Grid). Rename the output to NoPits.tif. Then connect NoPits.tif to D-Infinity Flow Directions (select Input Pit Filled elevation Grid). Double click on D-Infinity Flow Direction. Change the name of the first flow direction output to FlowDir.tif. Then change the second output to SlopeFrac.tif which means that the slope output is a fraction (rise over run) rather than percentages or degrees. Click OK. Make sure the slope output is above the flow direction output. Connection the Flow_Dir.tif output to D-infinity Contributing Area (select Input Infinity Flow Direction Grid). Change the third output name to FlowAcc.tif. Save your
Page 7 of 16 model. Run your model and save it again. It should appear as given in Fig. 2.3.6. Figure 2.3.6. Creating a depressionless DEM and calculating slope, flow direction, and flow accumulation with TauDEM. Next, Raster Calculator will be used to conduct grid math. In ArcToolbox, close the TauDem Tools and expand the Map Algebra toolset in the Spatial Analyst Tools toolbox. Drag Raster Calculator (Fig. 2.3.7, Arrow a) thrice into your model at the three locations indicated by Arrows b, c, and d. Be sure to reposition the output datasets as shown in the image. Figure 2.3.7. Calculate adjusted slope, specific catchment area, and topographic wetness index. To rename the output rasters, double click on the output circle, delete the information in the text box, and type a new name. Specifically, the new name for the uppermost Raster
Page 8 of 16 Calculator tool (2.3.7, Arrow e) will be Slope, an abbreviation for Adjusted Slope. The new name for middle Raster Calculator (Arrow f) will be Wetness, an abbreviation for Topographic Wetness Index. Rename the lower Raster Calculator (Arrow g) output SCA, an abbreviation for Specific Catchment Area. The output slope map from TauDEM (Arrow e) must be adjusted because slope will be used in the denominator in the calculation of the topographic Wetness Index (Arrow f). Since it is not possible to divide by zero and your slope map will likely have areas with slope values of zero, replace all zero values with a small number (i.e., 0.000001). To do this, use the Conditional Evaluation (Con) function. To perform this operation, double click on the top Raster Calculator (2.3.7, Arrow b) and click with the mouse on the Layers and Variables, the numbers and operators, the mathematical functions, and the comma key on your keyboard to enter the following formula: Con("%SlopeFrac.tif%" > 0.0,"%SlopeFrac.tif%",0.000001) Click OK. Observe how connector lines were draw for you by the software. You can interpret this formula as follows: for input slope raster values that are greater than 0, then the output will be equal to the value of the slope raster; otherwise, values on the slope raster will be equal to 0.000001. Click OK. Then right click on Raster Calculator and click Run. If the procedure ran correctly, you will see a grey shadow behind the green output circle. If you receive an error message, carefully examine your formula. Next, the specific catchment area will be calculated from the flow accumulation output. The output for Flow Accumulation calculated with TauDEM was the sum of all upslope grid cells times the grid increment. To calculate the specific catchment area, multiply the Flow Accumulation output by the grid increment. Recall that in our case the projected DEM grid increment was 9.261174 m. The value you recorded in your notes for your projected raster may have been somewhat different. Double click on the third Raster Calculator (3) tool (Arrow d) next to the SCA output. Using your mouse, input the formula to multiply the Flow Accumulation output by your recorded grid increment. Click OK. Then right click on Raster Calculator (3) and click Run. Is the grey shadow behind the green output circle? If you receive an error message, carefully examine your formula. The next task is to calculate the topographic wetness index. To calculate this terrain attribute, you will need to refer to Eq. 2.4 in Chapter 2 of the book. Double click on the second Raster Calculator (2) (Arrow c). Use the mouse to key in the function. Note that you will need to use the natural log function {i.e., ln()}. Additionally, Tanβ is the fractional slope (i.e., rise over run) and you just calculated this with raster calculator using the Conditional Evaluation function. After you have entered the formula, click OK. Run Raster Calculator (2). Do you see the grey shadow? Your model should look similar to our example in Fig. 2.3.7. Next, more terrain modeling tools will be added to the model. The Spatial Analyst tool box should still be open in ArcToolbox. Compress the Map Algebra toolset (by clicking the minus sign, Fig. 2.3.8, Arrow a), and expand the Surface toolset (by clicking on the plus sign, Arrow b). Drag the Aspect (Arrow c), Curvature (Arrow d), Contour (Arrow e), and Hillshade (Arrow f) tools to your map to the locations on your model indicated by Arrows g, h, i, and j. Be sure to move the output circles to the locations as shown in Figure 2.3.8. Double click on the output datasets and change the file names to SAspect (Arrow k), CurveGen (Arrow l) CurveProf (Arrow m), CurvePlan (Arrow n), Contours.shp (Arrow o), and HillSh (Arrow p). Now click on the Connect tool in ModelBuilder and connect NoPits (Arrow q) to
Page 9 of 16 the four terrain tools (Arrows g, h, i, j). The colors should have changed for all except the Contour tool (Arrow p) and its output. Double click on the Contour tool and set the Contour Interval to 1-m. Click OK. Double click on the Curvature tool and check the last two fields. The raster names for Output Curvature Raster should be CurveGen, the name for Output Profile Curvature Raster should be CurveProf, and the name for Output Plan Curvature Raster should be CurvePlan. Right click on each of these four tools and run. Figure 2.3.8. Calculate Aspect, Curvature, Contour, and Hillshade.
Page 10 of 16 Close the Surface toolset within the Spatial Analyst toolbox and open the Math toolset. Grab and drag the Times tool (Fig. 2.3.9, Arrow a) with your mouse to the location indicated in the model Arrow b). Reposition the output as indicated in the figure (Arrow c). Then double click on the output circle (Arrow c) and set the name of the raster to PerSlope. You will use the Times tool to multiply slope times 100 so that you your slope map will have units of %. Use the Connect tool to draw a line from the Slope output to the Times tool (Chose Input Raster or Constant Value 1). Double click on the Times tool. Set Input Raster or Constant Value 2 to 100. Click OK. Move the blue input raster to the location indicated in the figure (Arrow d). Right click on the blue circle and rename it 100. Figure 2.3.9. Calculate percent slope
Page 11 of 16 The raw topographic wetness index and the specific catchment index maps will be difficult to visualize for conservation planning in their current form. Within the Math Toolset expand the Logical Toolset. Grab and drag two copies of the Greater Than tool (Fig. 2.3.10, Arrow a) and place them in the model as indicated in the figure (Arrows b and c). Then, reposition the output rasters as shown in the example (Arrows d and e), rename the top raster GR_WET (Arrow d), and rename the lower raster GR_SCA (Arrow e). Next, connect the Wetness output (Arrow f) to the top Greater Than tool (Arrow b; select Input raster or Constant Value 1) and connect the SCA output (Arrow g select; Input raster or Constant Value 1) to the lower Greater Than tool (Arrow c). Double click on the upper Greater Than tool (Arrow b) and set Input raster or Constant Value 2 to 14. Double click on the lower Greater Than tool (Arrow b) and set Input raster or Constant Value 2 to 1000. Reposition the two new blue input circles to the locations indicated in the figure (Arrows f and g). Use a right mouse click to rename the top input Wetness Threshold (Arrow f) and the lower input SCA Threshold (Arrow g). Save your model. Run both Greater Than tools. Figure 2.3.10. Adding thresholds for the Topographic Wetness Index and SCA.
Page 12 of 16 Creating Maps Now you will create attractive maps. Minimize your ModelBuilder (the minus symbol in the upper right). Then click on the Catalog tab on the right side of the screen. Navigate to the Results directory. Find your NAIP dataset. In our case, this raster was named NAIP12. Drag it to your map window. Right click on the NAIP imagery in the layer tab and select properties. Click on the Symbology tab and set the stretch type to Standard Deviation and set the Standard Deviation to 1. Turn off the Gama Stretch. Set the stretch statistics to From Current Display Extent. Contour Maps. Your map window should look as it does in Fig. 2.3.11. Figure 2.3.11. Contour map of field. In the lower left hand corner, Model Builder will be minimized. Restore the window by clicking on the first icon with double rectangles. Right click on the green HillSh circle, click Add to Display, and then minimize model builder. In the table of contents, right click on the hillshade map and select properties. For stretch type, chose Standard Deviations. Change the Standard Deviation to 1. Scroll down and change the drop down box under Statistics to From Current Display Extent. Click on the display tab and change the transparency to 50%. Click OK. This map was created from USGS DEMs. If it had been created from LiDAR, you would be able to see much more detail. In the map Table of contents, turn off the Hillshade layer. Does your example look similar to our example in 2.3.12?
Page 13 of 16 Figure 2.3.12. Hillshade map of field. Next, you will create a slope map with contours. Turn off the HillShade Map, restore ModelBuilder, right click on PerSlope, add it to the display, and view Map Properties. On the Symbology tab, set Show to Classified. Open the classification method by selecting the Classify button. Set the classification method to Quantile, and click OK. Set the classes to 5 and click OK. Select the color ramp that goes from yellow to red. Right click in the white area below labels and chose Format Labels. Under Rounding, click on the circle next to Number of Decimal Places. Set the number to 1. Click OK. Click OK again. Go to ModelBuilder and add the generated shapefile Contours to your view. On the Symbology tab for Contours, change the color of your lines to black and the width of your lines to 1.5. If you are in an area of rapidly varying terrain, you may need to reduce the width of the contour lines. Your map should look similar in some ways to our example in Fig. 2.3.13. Does this map help you better visualize the slope map? Figure 2.3.13. Contours.
Page 14 of 16 Your contours, with other layers, can also help you visualize terrain. You can also turn off your slope map and turn on your Hillshade map for a different perspective (e.g. Fig. 2.3.14). Does your map with contours, semi-transparent hillshade, and NAIP imagery in the background help you visualize valleys and ridges? Next, make a Plan Curvature Map. From ModelBuilder, add the CurvProf layer to ArcMap. Right click on properties, chose the color ramp that goes from red to green, change the stretch type to Standard Deviation, change the n to 1, and the stretch Statistics to From Current Display Extent. In our map, there were striking differences in curvature associated with landscape position (Fig. 2.3.14). Look in Chapter 2 of the text for help interpreting your map. Figure 2.3.14. Contours with HillShade Next, create a Specific Catchment Crea map. From ModelBuilder add GR_SCA. Select the display Layer Symbology tab, and double click on the color tile next to the 0 value and set to No Color. Change the color tile next to the 1 to black. Click on the display tab and set transparency to 25%. How does the map created with USGS 10-m DEM data (Fig. 2.3.15) compare with the specific catchment area threshold maps created in Chapter 2 of the textbook, that were created with LiDAR data? How does our map compare to yours? If you are not happy with your map you can try using a different threshold value when calculating the SCA in ModelBuilder. To do this, it is wise to save the map style so you do not have to reset it. First, in ArcMap go to the table of contents and right click on gr_sca. Then click as Save as Layer File. Navigate to the c:\gis4cons\chap02\ directory, save as Terrain_thresh.lyr, and click SAVE. Then go to Model Builder and associate the style to the raster output. To do this, right click on GRA_SCA, select Properties, click the Layer Symbology, click on the folder icon, navigate to the c:\gis4cons\chap02\ directory, click on Terrain_thresh.lyr, click Add, and then click OK.
Page 15 of 16 To reset the threshold, double click on SCA Threshold in your TerrainAttributes model in ModelBuilder and enter a different value. Then right click on the Greater Than (2) yellow tool and click Run. Then right click on GR_SCA, turn off Add To Display and right click again to turn it back on. It will be added to your map again. In the future if you want to change the threshold again you only need to do two things. First adjust the threshold and then turn on and off the layer from Model Builder. Go back and save layer files for all previously created maps and link the layer files to your output data files in Model Builder. Figure 2.3.15 Specific Catchment Area.
Page 16 of 16 Finally you will make a Topographic Wetness Index Map. Turn off the gr_sca layer. In Model Builder, right click on GR_WET and chose Properties. Under Layer Symbology, click the yellow folder and click on Terrain_thresh.lyr. Click Add and OK. Then right click on GR_Wet and add it to the map. Our topographic wetness index map (Fig. 2.3.16) was similar to (Figure 2.3.15). How did this map compare to the one we created with ArcGIS? How does it compare with your map? How could you use this map for conservation planning? Troubleshooting Figure 2.3.16. Topographic wetness index. Errors when using ModelBuilder are not uncommon. It is recommend to perform these steps sequentially to see if the problems can be resolved. In ModelBuilder, go to Model, Delete Intermediate Data. Then go to Model, Validate Data. Try to run the model again. If you still get errors, go to the next step. Save your work, close and restart ArcGIS. If errors persist, go to the next step. Save the Model and your ArcMap file. Shut down Arcmap. Go to the Windows Start Menu, click on All Programs, ArcGIS, and ArcCatalog. Navigate to C:\GIS4Cons\Chap02\Terrain.gdb and delete the entire contents of the geodatabase. Then delete Terrain.gdb. Right click on the Chap02 folder, create a new file geodatabase, and name the geodatabase Terrain.gdb. Restart ArcGIS. Try to rerun your model.