Panchromatic Image Sharpening of Landsat 7 ETM+ Using ENVI


THERE are a number of methods within ENVI that enable pan-sharpening. This tutorial provides step-by-step guidance on how to perform the image transformation. For more information on the differences between the pan-sharpening methods, the preferred pan-sharpening method based on specific user needs, and the output differences resulting from the different methods, please refer to the ENVI help documentation. A header file is required to perform Gram-Schmidt Spectral Sharpening, PC Spectral Sharpening, or CN Spectral Sharpening. Because GeoTIFF files do not have a header file, and all Landsat data are currently distributed in GeoTIFF format, these methods will not be included in the following examples.

The following steps explain how to pan-sharpen Landsat ETM+ imagery in ENVI using either the HSV or Color Normalized (Brovey) methods.

1. Open ENVI
2. From the main menu, click File -> Open External File -> Landsat -> GeoTIFF

ENVI Main Menu
3. Navigate to the folder where the image files are saved, highlight all of the bands using the SHIFT key function and click Open; the Available Bands List display box will appear with the bands that you selected
4. Next, from the main menu, click Transform -> Image Sharpening and select either the HSV or Color Normalized (Brovey) method.
Image Sharpening Options
5. Within the Select Input RGB Input Bands display box, select the multispectral RGB combination that you would like to pan-sharpen and then click OK
6. Next, within the High Resolution Input File, select the panchromatic band (*_B80.TIF)
7. Leave the Spatial Subset as the default of Full Scene and click OK
8. From the next display box, select the resampling method by clicking on the dropdown arrow next to Resampling and select one of the following options: Nearest Neighbor, Bilinear, or Cubic Convolution
9. Next, click Choose and navigate to the location where you would like to save the output data
10. Provide a file name for the output data and click Open
11. Click OK to initiate the resolution merge (please note that it may take a few minutes to run the resolution merge; you will receive an error message if there is not enough space to perform and save the output data to the specified location)
Color Normalized Sharpening Parameters Display Box
12. After the resolution merge has been performed the new pan-sharpened RGB bands will be added to the Available Bands List
13. Ensure that the correct bands are displayed in the RGB fields and click Load RGB to display

Available Bands List
14. To compare the pan-sharpened image to the original three-band multispectral 30-meter composite, click on the Display #1 button within the Available Bands List and select New Display
15. A new set of image windows will appear and the display button will change to Display #2
16. Ensure that the radio button is set to RGB Color and select the three bands that were used during the pan-sharpening process and then click Load RGB
17. To geographically link the two displays together, click Tools -> Link -> Geographic Link... from the menu bar within one of the images
18. Within the Geographic Link display box, click the arrow buttons next to both displays so that they both change to On and then click OK
Geographic Link Display Box
19. The pan-sharpened image and the original 30-meter data are now linked (the images below show a comparison between pan-sharpened Color Normalized (Brovey) data on the left and 30-meter data on the right)

Comparison Between Color Normalized and Original Data

USGS.Gov
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