5. Merging Two Images

Merging two images will show differences between two images of the same location in two different times, such as how the vegetation has changed between 2 years, how a city has grown, or how much area was affected by forest fires over the years.

To merge data from two images, you must have downloaded two images of about the same area but from different times. One of the images should be a subset/smaller area image. It is recommended that you download/subset the earlier date, just to establish a system, but this action will not affect your ability to merge images.

These 2 step directions will help you link a second image to the first subset image so that changes between the two images can be observed. (If the images do not merge, it may be because the size limit was exceeded. Try using a smaller subset.)

First Step: To make the areas in both image be the same location:

1. Open MultiSpecUniv
2. Select File. Select Open Image. Select your subset image. Select OK the on next 2 screens.
3. Select File. Select Open Image. Select the second image. Wait until it loads.
4. Select/bring forward your subset or smaller area image.
5. Select Edit. Select “select all image”.
6. Select Edit. Select “selection rectangle” Select Units: SELECT LAT-LONG. Also, CHECK BOX LABELED “apply to all image windows”. Select on OK. If a window pops up saying minimum or maximum limits are exceeded, check OK. Increase or decrease the lat-long numbers a small amount until the popups stop. There should be a rectangle drawn on the second image.
7. Select the second image to bring it to the front. Select Processor. Select Reformat. Select Change Image File Format. Select OK in next screen. Rename your file with a descriptive name. Be sure to keep .tif extension. Wait until the image is reformatted (100% complete).
8. Close both images. NOT DONE YET.....

Second Step: To link the 2 images together:

1. Select File. Select Open Image. Select the first subset image (.tif file). Click OK in next screen. Wait.
2. Click file. Click open image. Select your second subset image. Select the box labeled: “link to active window” Select Open. Select cancel in next window.
3. Select Processor. Select Reformat. Select Change Image File Format. In next popup (In "Images File Format Change Options" be sure Channels is set to "All".) Select OK. Rename your file -it is recommended to keep the original title, just add a phrase before the title. Keep extension .tif Click Save. Wait. Note: when opened it will start with <L2> indicating 2 images were linked.
4. Close image.
5. To see if it worked: Select File, Select Open Image. Select merged image. Select Processor. Select “Display image” in Type box “select side by side channels”. Zoom out. If the process worked, you will have a sum of the number of images in the original images. Sometimes ratios of bands help detect certain features better, such as a NDVI (Normalized Difference Vegetation Index). To ratio bands go to the page "Spectral Rationing".