Example 2: Hawaii – exploring its waters

Courtesy of USGS Science for a changing world
http://astrogeology.usgs.gov

Mauna Loa on the big island of Hawaii is the highest mountain on earth but we don't think of it that way because the bottom half of it is under water. It has some of the most diverse climate on the planet ranging from tropical rainforest around its biggest town Hilo (infamous for being frequently destroyed by tidal waves), to clear sub-arctic conditions at its summit to desert conditions in its rain shadow.

Step 1:
Open the image-processing program. If you installed IrfanView program open it.

Step 2:
Click on the image of Hawaii to open a larger version and save it to your computer

(Hawaii1.jpg).

This is a multi-spectral can image of Hawaii in false colour from Landsat 5 downloaded from a NASA site in Maryland, West Virginia. The image is supplied in 16 million colours and you will be instructed on how to quantize it to 256 colours. The circular feature on the left is the crater of this enormous volcano.

Step 3:
Open the saved the image of Hawaii from within the image-processing program.

Step 4:
Change the image to 256 colours. Within Irfan's menu select Image > Decrease colour depth > select 256 colours.

Step 5:
To complete the process click O.K.

Now we can enhance the image to find our more about the water.

More about the water

Notice the water in this image has been changed to black. Is there any standing water on the island itself? The answer is yes but the differences are too subtle and the pixel size too small for the human eye to detect. Most of the ocean and some of the volcanic peak appear blue indicating standing water.

From within the image-processing program find the palette.
Within Irfan's menu select Image > Palette > Edit palette (you will have to do this three times).

First time:
Click on the square shown in the top left hand corner and change the black to blue. Click O.K.
You can now see places that have cold water - notice the island is surrounded by cold (deep) water but also that there is a supply of cold (due to the altitude) water in the crater itself.

Second time:
Click on the dark square 11 down and 6 from the left and change it to red. Click O.K.
This shows warm water. Notice it is a very narrow band around the island. The ocean becomes very deep very quickly around the island. Click O.K.

Third time:
Click on the dark square 8 from the left in the top row. Change it to aqua.
This colour shows water in creeks and streams. Some of it is partly obscured by cloud but the enhancement allows you to trace the hidden watercourses.