Hurricane Opal Project Activity These Links Are To Tutorial Activities Remote Sensing / Digital Numbers / Contrast / Brightness / Histograms / Measuring / Density Slicing / Particle Analysis / Density Calibration / DEMs / Elevation Calibration / Animation  / Tutorial Site Map Email: proof@proofofconcepts.com Digital Elevation Models You may print these instructions before starting this activity. USGS Image  The image at the left looks like a typical black and white photo, only fuzzier. It is a DEM. However, instead of displaying an image which shows a landscape or your girlfriend/boyfriend in which pixel values represent gray scale colors, they represent elevation. Download the Mobile.tif.sit image at the left and place it into your working folder. Open NIH Image and open this downloaded image into the NIH program. Drag the mouse cross hair around the image. Notice that the values of the pixel changes as it is moved around the image To learn about the numbers behind these types of images, click on the density profile tool. Then click on Options/Profile Plot Options. This is the dialog box that will appear.
	Do not change any settings, but press OK. Once the above procedures have been accomplished, click the mouse cross hairs on the image and drag it to another point, release the mouse button, once again "marching ants" will appear as well as the plot box. This plot box shows the range of pixel values along the length of the line. It does not show the actual elevation. Do several more of these types of plots. Also experiment with the PLOT OPTIONS by changing Fixed Y-Axis and Fixed Plot Size. For actual elevation the image must be calibrated. Another aspect of working with DEMs in NIH Image, is the ability to show contours of the land. Click on the rectangle tool. Click and drag and release this tool across a portion of the image. Click on Analyze/Surface Plot. The Surface Plot window appears. Leave the dialog box as is, and click OK. A wire frame contour is drawn of the area selected on the DEM. Download this DEM of Salt Lake City (salt.tif.sit) and practice with this image. Develop a surface plot of this DEM. Practice these surface plots and try changing some of the parameters in the Surface Plot window. Other programs can be used to convert DEMs into relief images such as this one of Mt. Madonna, California. Once this DEM is converted, another program can be used to render 3D images of the same DEM like this one of Mt. Madonna. Can you identify the same points on these two images? Look at this converted DEM of Mobile, Alabama. It was produced from the DEM at the top of this page. It shows very little relief compared to the one in California. The difference being that the Mobile DEM has a vertical range of 0 feet to 363 feet - Mt. Madonna has a vertical range from 240 feet to 2281 feet. Hurricane Opal Project Activity These Links Are To Tutorial Activities Remote Sensing / Digital Numbers / Contrast / Brightness / Histograms / Measuring / Density Slicing / Particle Analysis / Density Calibration / DEMs / Elevation Calibration / Animation  / Tutorial Site Map Email: proof@proofofconcepts.com