Working with Landsat imagery

We recently came across this image from NASA’s Earth Observatory, which shows smoke from fires on the island of Sumatra, Indonesia. Given the scale of the phenomena we thought it should be visible in Landsat imagery.

To get the imagery, we used the technique outlined in this post. Landsat 8 takes 16 days to cover the entire earth and adjacent strips of imagery are captured on different days. We looked for images close to the target date that showed some fire activity.

When you import an image into Google Earth Pro using drag-and-drop, it states that ‘the imported image is larger than the maximum size supported by the hardware’. There are options to create a super overlay, scale or crop the image. However, we found that if you scale the image, you can in fact edit the image overlay and set it back to the original unscaled image without problems.

We wanted to display multiple adjacent images, so we needed to get rid of the black background. We first tried editing the images and making the black background transparent. This did work, but it required saving the images as PNG files, because the JPEG format does not support transparency. But PNG files are significantly larger (about 10 times bigger for these files) and thus not suitable if you wish to share them with others. If you are just using Landsat imagery locally, then transparency might be the easiest solution.

So, what we decided to do was to use a graphics editing program (GIMP) to rotate the images and then crop out the black area, keeping them in the JPEG format. We could then use the previously created image overlays as a guide to create new overlays with our rotated and cropped images. To do this easily, in the properties of the image overlay, go to the ‘Location’ tab and click ‘Convert to LatLonQuad’. This makes it easy to line up all the corners with the existing image overlay.

It must be noted that some slight loss of image quality occurs and that image alignment is not perfect, but for our purposes is is good enough.

To see the results in Google Earth download this KMZ file. When looking at the fires and smoke trails, be sure to look at the scale in Google Earth.

About Timothy Whitehead

Timothy has been using Google Earth since 2004 when it was still called Keyhole before it was renamed Google Earth in 2005 and has been a huge fan ever since. He is a programmer working for Red Wing Aerobatx and lives in Cape Town, South Africa.






PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.

Comments

  1. Rather than rotating and cropping, just use the Magic Wand selection to delete all the black pixels, and save it as a PNG with transparency. I find that Adobe PNGs are smaller than GE PNGs.
    Another trick for replacing the imported image with an edited version is to swap the revised file for the one in your local C:\Users\name\AppData\LocalLow\Google\GoogleEarth\import folder, where all the .PNG files are stored. It’s not a perfect match, but it’s quick and easy.

    • Timothy Whitehead says:

      Using GIMP the PNG’s I got were too big to consider sharing (about 100Mb for all three), but would have been fine to use locally. Maybe Adobe has some better compression methods for PNG. To replace a modified image you can simply edit the overlay properties and select a new image.



PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.