I have been going through my now annual process of constructing a giant satellite image of Cambodia with images taken from the USGS Earth Explorer site, freely available at http://earthexplorer.usgs.gov/. To construct this ultra high-resolution image I had to search and download over 60 images, taken between mid December 2015 and the 16th Feb 2016. After doing this on a regular basis for some years, I soon came to realize that for 8 months of the year there is little chance of a clear image due to clouds.
If you want to use this site I suggest setting your range of dates to only include December to April each year, otherwise you will be trawling through hundreds of images that are useless. Also there are numerous image sets you can choose from but largely you will just want to select Landsat 8 for today or the older Landsat versions for historical images. Each month you get 3 or 4 pictures of each part of Cambodia and it takes a total of 25 of these images to make up a complete map of Cambodia.
For anyone wanting to put together an image from 2003 to early 2015, you have to contend with images from the faulty Landsat 7 satellite. As you can see they have lines across roughly 80% of the image, which makes them very hard to use.
Putting all these images together is a painstaking process and the end result is a truly ridiculous 5.3GB file. Even with my quite powerful Mac, saving it takes almost 10 minutes. But that’s the easy bit. Sometimes as many as 3 or 4 images are combined so as to remove cloud cover. I put in around 20 hours of moving, erasing, merging, colour correcting and otherwise tweaking the images, but I do have a pretty interesting result. Were you to print the final image at 72dpi it would be an impressive 13m x 7m.
This is a low-resolution version of the completed map.
I have blown up a few areas with comparisons to earlier years to give both an example of the detail of the full sized image and the destruction that’s taking place in Cambodia’s forests.
Below are screen shots from the EarthExplorer site.