Last week Google added global mosaics in historical imagery for each year going back to 1985. The mosaics are created from mostly Landsat imagery with a bit of Sentinel 2 imagery for the last couple of years (the Sentinel 2 satellite is new). The mosaics are created by gathering all the Landsat/Sentinel 2 imagery for a given year and looking for cloud-free and snow-free pixels then combining the images to create a single global mosaic for the year. Although it is fantastic for viewing long term change, the overall result is that we actually miss out on short term changes.
Back in July we wrote a post about watching sand dunes move with Google Earth imagery. Today we are looking at a similar concept, but with Landsat imagery instead. In August we created a KML file that automatically creates animations using Landsat imagery with thumbnails from Amazon Web Services. We used that tool to create the two GIF animations below:
Sand blowing in the Sahara (southern Libya). Explore original animation.
Sand blowing and irrigation circles in Oman. Note especially south west of the centre of the animation there are wisps of sand moving north west. Explore original animation.
What we found interesting is that established dunes hardly move at all over the three years covered by the animations, but loose sand can clearly be seen moving. It looks no different than sand being blown on the beach. Yet the scales involved in the animations are tens of kilometres and a three year period.
You will also notice in the second animation the dunes to the north east appear to pulse sharper, then softer again. This is because the angle of the sun affects the shadows during the course of the year.