My Google Map Blog

Google has recently done a minor imagery update. The only May image is a DigitalGlobe image of the Fort McMurray wildfire, although it does not include Fort McMurray itself. When we looked at the Fort McMurray wildfire a few days ago we noted that there is a wide variety of satellite imagery available. However, most of it is low resolution imagery not suitable for Google Earth and the high resolution imagery from DigitalGlobe is false colour imagery. We thought this might be a good time to make some observations about false colour imagery.

False colour imagery involves mapping different spectral bands to the colours visible to the human eye: red, green and blue. Read more about false colour imagery on Wikipedia and NASA’s Earth Observatory.

Earth observation satellites, such as Landsat and Sentinel, capture all their images in a number of bands and any image can be rendered in natural colour or various combinations of false colour. However, it would appear this is not the case for at least some of DigitalGlobe’s satellites as they often only have false colour imagery of certain events. False colour imagery is good for highlighting changes to vegetation caused by fire so DigitalGlobe had good reasons for capturing false colour imagery. But the fact that they don’t seem to have true colour imagery suggests that their satellites do not, by default, capture all wavelengths that they are capable of in every image. This is most likely due to data storage and transfer limitations on the satellites.

[ Update : We received feedback from DigitalGlobe (see the comments below) stating that they do, in fact, capture and store the visible wavelengths and if necessary could create true colour images for any location where they have false colour imagery. The reason why false colour imagery of Fort McMurray was shared is because infrared wavelengths penetrate smoke and highlight vegetation changes better than visible wavelengths (the false colour imagery we saw is most likely the Near Infrared, Red and Green bands.]

Google Earth has a surprising amount of false colour imagery. It is very common across the Sahara, Saudi Arabia and Indonesia. There are also some instances of it being used for particular events such as earthquakes and fires.

False colour greatly improves contrast in desert regions such as these sand dunes in the Sahara.

Sometimes it results in striking blues such as the above location in the Sahara that looks like the middle of the ocean.

False colour not only improves contrast but can distinguish between different types of sand, which in natural colour (the yellow areas) look nearly identical.

To find the above locations in Google Earth download this KML file.
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