Introduction to Remote Sensing

 

Viewing Remotely Sensed Imagery in ArcView

 

Start ArcView GIS

 

  1. From, the File menu, choose extensions.
  2. Click the Image Analysis check box.

  3. Click the OK button on the extensions dialog to load the extension.

 

 


View SPOT Image of Moscow

 

  1. Open a new view.
  2. Click the Add Theme Button 
  3. Navigate to the avtutor directory. Double click on the ia_data directory under the avtutor directory.
  4. Click the Data Source Types drop-down list and choose Image Analysis Data Source.
  5. Double-click on Moscow_spot.tiff to add it as a theme.
  6. Click the check box to draw the theme in the view.
  7. With the Moscow_spot.tif theme active, click the Edit Legend button  to display the Legend Editor dialog. Move it so it doesn’t cover the view.
  8. Click the Infrared button on the Legend Editor.

 

 

 

      Apply a Histogram Equalize Stretch to the Image Moscow

Standard Deviations is the default histogram stretch applied to images by the ArcView Image Analysis extension. You can apply a Histogram Equalize stretch to redistribute the data so that each display value has roughly the same number of data points.

 

  1. Click on the advanced button at the bottom of the Legend Editor.
  2. Move the Advanced Options dialog so that it does not cover the view. Notice the position of the input (black) and output (color) histograms prior to the next step.

 

The histogram of an image is a graphic depiction of the number of pixels (measured on the count axis) of each individual value (measured on the value axis) that make up the image. Look at the following example. The black histogram represents the input data file values. These are the actual values that make up the data. The color histogram represents the output values. These are the stretched values. You can alter the histograms of the image in a number of ways, including varying the type of histogram stretch applied to an image.

 

 

 

 


  1. From the Legend Editor, click the Stretch drop-down list and choose Histogram Equalize. Click Apply.
  2. Look at the histograms in the Advanced Options dialog. The values are now more evenly distributed.

 

 

A histogram stretch uses the data file values of the input histogram and a lookup table to reassign pixels to a new output (or stretched) values of the display. The term stretch is used because the data values that make up the original image typically fall in a narrow range of the possible display values. The stretching of the input data file values changes the brightness and contrast of the image as it is displayed in the view so features in the image are distinguishable.

 

  1. In Legend Editor, click and move the Brightness and Contrast slider bars either right or left. Click Apply. Note how the histograms and image change.
  2. You can experiment further with the position of Brightness and Contrast slider bars to see how they change the image. When you are done, click the Stretch drop-down list and choose Standard Deviations. Click Apply. This will return to the default stretch and prepare the image for the next set of steps in this exercise.

 

Apply an Invert Stretch to the Image Moscow

 

  1. In the Legend Editor, check the Invert Stretch  box.  Click Apply.

 

 

  1. Look at how the histograms and lookup tables in the Advanced Options dialog have changed. Click Undo in the Advanced Options dialog. The image is redisplayed with a Standard Deviations stretch applied to it.
  2. Close the Advanced Options dialog and the Legend Editor.