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Exercise 10 Spatial Analysis on Antarctica

Due: Thursday, February 27 by classtime. You will have 2 class periods to work on this lab and since it is so long it will count double for your assignment grade.

Goal: Using ArcMap’s Spatial Analyst tools for digital elevation models and rasters.

Datasets:

• Bed elevation raster dataset of orthometric elevations

• Ice thickness raster dataset of ice thickness

• Surface elevation raster dataset of orthometric surface elevations

• Coastline a polygon of Antarctica and the permanent ice shelves

• RockOutcrop a polygon of rock outcroppings

• Southpole a point shapefile with the location of the south pole

These data came from two sources: The Antarctic BEDMAP project and The Scientific Committee on Antarctic Research (SCAR) Antarctic Digital Database (ADD).

Data can be found in our class folder under Antarctica.zip:

Assignment:

Antarctica has all of the same complexities as the other continents on the globe: mountain ranges, streams, glaciers, valleys, plains, inland seas and islands. However, much of this topography is hidden from our view by the vast glaciers and ice sheets that cover the continent. With recent advances in remote sensing technology, we now have data available to us to make maps of what lies below the ice in Antarctica. These maps can help us answer a wide range of lingering questions about Antarctica. Exactly how much ice is there? What would it look like if all of the ice melts off? Due to isostacy, how high would the land mass rise if the ice were gone?

Part 1 – Spatial Reference

If we look at the metadata as it is, we see that all of the data are currently in a Projected Coordinate System (PCS):

PCS type: South Pole Stereographic Linear Unit: meter Latitude of Origin: -90.00000 Central Meridian: 0.00000 Standard Parallel: -71.00000 False Easting: 0.00000 False Northing: 0.00000 Datum: WGS84

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As of ArcGIS 9 (we are using ArcGIS 10) there is a predefined PCS that matches this. However, for practice we will modify an existing PCS.

• Open a new empty map

• Right click on Layers in the Table of Contents

• Select Properties to open the Data Frame Properties window

• Select the Coordinate Systems Tab

• From here Select a Predefined Coordinate system following the path: Projected Coordinate Systems > Polar > South Pole Stereographic

Notice how the parameters do not match those of the PCS above? We will now modify this existing PCS:

• Double click the coordinate system's name.

• Enter a new name (we will use SCAR Antarctic)

• In the projection Box, under name, use the drop down menu to selectStereographic_South_Pole

• Change the value for the Standard Parallel to match the above value (-71.00000)

• Click ok

• Click the Add to Favorites button so that this PCS can be used again

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If this doesn’t work for you, remember that ArcMap can project “on-the-fly”. By adding any of the data into ArcMap, the PCS will be automatically set, and any other data that are added will take on that PCS. (In ArcMap, the Data Frame always uses the PCS from the first file added.)

Part 2 – Organizing and exploring the data

Add all the files from the Exercise Data.

• Add the following files first: Coastline, South Pole, Rock Outcrop. Note that these are allshapefiles.

• Next, add the Surface Elevation (surfel), Bed Elevation (bedel) and Ice Thickness (icet)files. For the time being, toggle off the Bed Elevation and Ice Thickness files.

• Because the current display is “stretched” the result is a map with little range in thegrayscale.

o To change the “stretch” right click on the file SurfaceElevation to navigate to theLayer Properties window.

o Select the Symbology tab, scroll down, and in the statistics drop down menuselect “From Current Display Extent” and click OK. What do you see now?

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Questions to be handed in!!

1. Right click on the surfel layer, hit source tab, scroll down...what is the resolution or cell size(this value is in meters), pixel type (integer or floating point), pixel depth (in bits) and numberof bands of this raster data set. Make a chart like the one below:

Raster Layer Resolution (km) Pixel Type # of bands Pixel Depth (bits)

2. What are the Mean, Maximum and Minimum elevations of the raster

dataset? (Hint - found in the Source tab of the layer)

3. What is the Default Stretch Type of the Surface Elevation raster?

Back to the Layer Properties window…

Changing Symbology:

• In the Symbology tab, on the left choose Show: Classified.

• (Arc may ask if you want to compute a histogram, if so, choose yes)

• Then, click on the Classify button to the right to bring up a new window.

o Classification Method: Defined Interval; to group the interval by a setting that youchoose

o Interval Size: 200; this is what your contour interval will be

o Click Apply

1b. In your own words, explain what is meant by pixel depth.

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• Once back at the Layer Properties window, choose a color ramp.

o Left clicking once on the “Symbol” bar will allow you to flip the color rampo Click on the “Label” bar to see the formatting for the labels

• Now change the symbology of the Coastline file by double clicking on the coloredsquare. Choose “Hollow”.

o Now move the coastline layer above the elevation file in the table of contents.

Your resulting map shows the elevation at 200 m intervals. It should look like the one below:

Make a screen shot of this map, and save it to your word document. Then, to make the map look nicer, we will remove the boxes around the continent…

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Part 3 – Spatial Analyst Extension

All of the work that we will be doing in this section will be in the Spatial Analyst Extension

• First you’ll need to turn on the Spatial Analyst extension. Do this by clicking onCustomize on the main tool bar. Then choose extensions. In the Extension window,make sure that the Spatial Analyst box is checked.

• You can also right click on the top of the screen and add the Spatial Analyst Toolbox.Analysis Mask

• In the Geoprocessing menu at the top of the page, select Environment settings (seeimage on the next page). Scroll down and extend the Processing Extent tab

o Extent: Default; the extent is what the area of analysis will be. This allows for anarea to be analyzed without being clipped.

Scroll further down to the Raster Analysis tab.

o Cell Size: Maximum of Inputs; this means that when two or more rasters arebeing used, the new raster will not have any cells that are smaller than the cellsfrom any of the input rasters.

o Mask: Coastline; defines the cells within the analysis extent. For us, this meansthat the only cells that will be analyzed will be within the coastline of Antarctica.

• Click OK

Extract by Mask By clipping the elevation file to match the coastline of Antarctica, we will restrict the symbology to just the continent and its ice shelves. So now, the map will match the Analysis mask that we just made.

• Open ArcToolbox and follow the path Spatial Analyst > Extraction > Extract by Mask

• Input Raster: SurfaceElevation; this is the raster that is going to be clipped

• Input Raster or feature mask data: Coastline; this is the layer that defines where to clipthe above raster

• Output Raster: **Browse to the folder that you want this stored in and name the fileSurfClip

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Creating A Hillshade Using a hillshade in conjunction with a semi-transparent elevation grid creates a nice effect.

• In the Spatial Analyst toolbox, expand Surface and select Hillshade

o Input Raster: SurfClip; this is the layer that the hillshade is drawing its informationfrom.

o Output Raster: ***Browse to the folder that you want this stored in and namethe file HillshadeS.

o Leave everything else at its default setting, see Tool Help if you’d like to learnmore about the different parameters.

• Once you have your hillshade made, go to Layer Properties > Symbology, and set theStretch Type to Standard Deviations, with two or less deviations. (In the window this will bethe box that indicates n: and feel free to leave it at two).

• Now, drag your SurfClip layer on top of HillshadeS, and give it 50% transparency.Import the symbology of Surface Elevation layer and then turn off the Surface Elevation layer.

• You might want to turn on the Effects Toolbar and adjust the brightness/contrast of your

hillshade to get a spiffier (less drab) result, or play with the type of stretch in symbology.

Your map should now look something like this (remember to leave your Coastline, SouthPole and RockOutcrop files toggled on so that they appear on the map): Make a screenshot and include in your write-up.

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Questions to be handed in !!!

4. The highest point in Antarctica is the Vinson Massif (a.k.a. Mount Vinson), in the EllsworthMountains.

a. Using the SurfaceElevation raster, find the cell that contains the top of Mt. Vinsonand give its latitude and longitude, in decimal degrees. Hint: the selection toolsin the Selection menu do not work with raster data. Change the symbology tohighlight cells over 4080 meters. Make that class of cells red for ease ofidentification. Zoom in and use the Identity tool from the toolbar (blue circlearound an “I”) to get the highest elevation value. To get locations in decimaldegrees, you can set the display units of the Data Frame in the Data FrameProperties window or the dropdown arrow in the Identify tool results box.

b. Find the height of Mt. Vinson on the internet. What is it? Give a plausible reasonwhy the known height doesn’t match the height in our DEM.

c. What is the elevation of the cell that contains the South Pole?

Continuing on with Part 3 – We will now be working with the bedrock data

The "bedel" raster shows the topography beneath the ice on the continent, and also shows the bathymetry of the sea floor. You’ll notice this layer forms a giant circle- the layer extends to 60° South latitude in all directions.

• Follow the above directions, using the BedElevation file. So in the end, you should havea map that looks just like your SurfaceElevation map does now.

o When you extract by mask, name your new file BedClipo When you make your hillshade, name your new file HillshadeBo Create a similar layout, with HillshadeB being a lower layer, BedClip should be

on top of that layer, with transparency set to 50%

o Again, don’t forget to include the Coastline, SouthPole, and RockOutcrop files.

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Questions to be handed in!!!

5. What are the mean, maximum and minimum elevations for the continent? Hint: Check thesource tab in the file’s properties.

More Spatial Analysis!

Creating a Binary Raster In the map above, some parts are above sea level, and some are below. We can’t tell the difference by just looking. By creating a binary raster, we will have only two values. In this case we will set the values as above sea level, or below sea level. Then we’ll use symbology to create a map that can show us exactly what parts of Antarctica would be below sea level.

• Open the Raster Calculator in ArcToolbox by following the path Spatial Analyst > MapAlgebra > Raster Calculator

• We will be using a conditional statement, so begin by double clicking “Con” listed in thebox on the right

• Then, in the box on the left, double click on BedElevation

• Using the keys in the pad above, your statement should read:

o Con(“BedElevation” <= 0,1)

• Output Raster: **Browse to the folder you want to store this file in, and label itBinaryWater

• Now, make the water areas blue and slightly transparent, and move it above theHillshadeB and BedClip layers in the Table of Contents. Keep the Coastline,SouthPole, and RockOutcrop layers on.

Questions to be handed in!!

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6. Explain, in words that include “if… then…”, the meaning of the conditional statement used togenerate the binary raster above. Hint: Use ArcGIS destop help and search “conditionalstatement” for explanations of similar examples

Creating a Contour Line

Looking at the map you just made, wouldn’t it be nice to add a black line around the water? In this situation, the easiest way to do that is by making a contour line.

• From the Spatial Analyst tool set, select Surface > Contour

o Input raster: BedClip; this is the raster that will provide the data on whichthe contour lines will be set.

o Output polyline features: **Browse to your folder, name the fileBedContour

o Contour Interval: 4440 (this will mean we only have one contour, becausethe highest elevation of the bed is 4364m).

o Base Contour: 0

o Z factor: 1

• Set the contour line to Black in color, with a width of .5

Your map should now look something like this (see image below):

Make a screenshot and include in your write-up!

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Questions to be handed in!!!

7. Although I downloaded this ice thickness raster, we could have created one from the fileswe’ve worked with so far. How? Give your answer in a list of steps (general steps andalso specific steps for doing this in ArcGIS).

8. How thick is the ice at the South Pole? What is the maximum ice thickness and where isit located (in lat/lon decimal degrees)?

Calculating Ice Volume and Area For this, we will be using the 3D Analyst Extension. To turn this on, be sure to go to “Customize” on the main menu, select Extensions, and toggle on 3D Analyst.

• Open ArcToolbox > 3D Analyst > Functional Surface > Surface Volume

• Then use these settings:

o Input Surface: IceThickness; this is the layer that Arc will use to make thecalculations.

o Output Text File: **Browse to your folder and title this file IceTableo Reference Plane: ABOVE; this tells Arc whether to calculate above or

below a certain heighto Plane Height: 0o Z Factor: 1

• Click OK

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• Open your table once the calculations are complete (you’ll have to go to yourfolder to open the file to Excel).

o Do this by opening Excel,o select open from File on the main menu, browse to your foldero Files of type: All fileso Select IceTableo Now you’ll be in the Text Import Wizard window

• Original Data Type: delimited; click Next• Delimiters: Commas; click next• Column Data Format: General; click Finish• Now your data is in a pretty Excel graph

• The statistics given give the 2D area (plan view area), the 3D area (area of

the irregular surface defined by the top of the ice-thickness raster when the baseis assumed to be level) and the Ice Volume (2D area x sum of all cell values).The units for the results are the same as the spatial reference, in our casemeters.

Questions to be handed in!!!

9. What is the volume of the Antarctic ice sheet and ice shelves/tongues, in cubic kilometers?

10. What is the surface area, in square kilometers, of Antarctic ice?

Isostatic Rebound- Spatial Analyst Isostasy refers to a process that restores equilibrium after a load is either added to or removed from a tectonic plate. As ice melts off of Antarctica, it will lighten the load of the plate, and the underlying continent will rebound, rising upward. The total amount of rise can be modeled as being directly proportional to the thickness of the ice and the ratio of the density of the underlying mantle to that of the ice. Specifically, for individual raster cells:

(Density of Ice/Density of Mantle) X (Ice Thickness) = Elevation Change

o Average density of ice: 0.98 g/cm3

o Average density of mantle: 3.34 g/cm3

o For today, use the density ratio of ice to mantle equal to .2825

To obtain an elevation raster for the continent that includes this elevation difference we will:

o Step 1: Multiply an ice thickness raster by 0.2825 to obtain elevation changeo Step 2: Add the resulting raster to the bedrock elevation raster to obtain

isostatically compensated elevations for the Antarctic continent

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Step 1 multiplies an integer raster (ice thickness) by a floating point value, resulting in a floating point raster.

• Open the Raster Calculator (Spatial Analyst > Map Algebra)

• Enter the expression “IceThickness” * 0.2825, using the buttons given

• Browse to your folder and save this file as ElevChange

• Click Okay (this may take a moment, be patient)

• Now, open the Raster Calculator again, and load the new file (ElevChange) and add it(use the + sign from the buttons) to the BedElevation raster.

• Browse to your folder and save this file as BedIsostasy (again, give this a minute toexecute)

Use some symbology to dress up your map:

• Symbolize your new raster

• Create and save a Hillshade

• Create another zero elevation contour

Questions to be handed in!!

11. How do the mean, maximum and minimum elevations for the continent after isostaticrebound differ from those of the sub-ice topography before rebound (see question 5).

Greenhouse Antarctica The south polar ice cap accounts about 91.5% of the ice in the world. If it were to melt, the sea level would rise by about 73 meters. If all of the ice on the planet were to melt, sea level would rise by 80.5 meters. Now, we’ll produce a map that shows higher sea level. SAVE OFTEN!

• Use Raster Calculator to subtract 80.5 meters from the cells of BedIsostasy.

o Name this one yourself, but be sure to remember the file name

• Make a Hillshade of this new raster.

• Create a binary raster of the regions above and below sea level.

o Again, be sure to keep track of your file names

• Create a shoreline

o Think about what contour interval you want to use here!

• Symbolize the results and make an attractive map.

Questions to be handed in!!!

12. Make a screen shot of this final map and paste it into your word document. Be sure toinclude a grid and a scalebar.

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13. Explain why, for this map in particular, it would not make sense to put in a North arrow.

14. The USGS has calculated volumes of ice for Antarctica that are substantially larger than

those you calculated. The USGS calculated 30.1 million km3. Why do you think your resultsare different?

Your final map should resemble something like this…

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Part 4: Final Bits!

Your professor recently returned from searching for meteorites in the Davis nunataks and Mt. Ward region of the southern Transantarctic Mountains.

Download the ANSMET.zip file from the Data folder on our website, unzip it, and add both the PolyData.shp and PointData.shp to your map. The single point is McMurdo Station on the coast of Antarctica. (Right-click on the point layer name and click “Label Features”) The polygons are our search areas while camped out on the ice.

Question to be handed in!!

15. Brian flew from McMurdo Station directly to Davis-Ward on a Basler (DC-3) aircraft, with acruising speed of 330 km/hr. How long did the trip take in this non-pressurized, non-climate-controlled (COLD!) airplane?

16. What is the southernmost latitude Brian went to while searching for meteorites? Report youranswer in decimal degrees. (Hint, under View>Data Frame Properties>Units>Display you canselect decimal degrees and then scroll on the map with the coordinates appearing in the lowerright.)

17. The meteorite team got invited to South Pole Station’s Christmas party (not really, butcontinue). If we navigate crevasses and other hazards at 30 km/hr on our snowmobiles, whenshould we have left camp to get to Christmas Dinner? Dinner was at 6 pm on December 25, butwe wanted to show up at 5:30 for a shower, to wash away the weeks of stank.

Now we want to determine how much area this adventurous team of 8 explored in their quest for space rocks. To calculate area of polygons, you need to first create a new field in the table and then use the “Calculate Geometry” function, as described below.

• Open the polygon attribute table. Add a Field called area__sq_m that is data type: floatwith a value of 10 for both precision and scale.

• Once created, right click on the column heading and select “Calculate Geometry”. Youshould be able to leave all the defaults (Property “Area”, Coordinate System “PCS:South Pole Stereographic” and Units “Square Meters”).

Final question to be handed in!!

18. Given weather and transportation logistics, we spent a total of 30 days actively searchingfor meteorites. How many square kilometers did we have to search per day to cover the totalarea within the polygons?

19. Finally, make a table reporting the maximum, minimum, and average values of Elevationand Ice Thickness within the search areas (polygons). (Hint: You used tools to do this type ofoperation earlier in the lab.)