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The Google Earth new global mosaic: a deeper look

June 29, 2016

Google recently refreshed Google Earth’s global mosaic with newer, sharper imagery. So far, we like it very much and think it is definitely an improvement. However, we will have a look around and see if we can find any flaws or interesting aspects to the new imagery.

Landsat 7 stripes

We already pointed out yesterday that although Landsat 8 imagery was used in the new mosaic, it is not entirely free of Landsat 7 imagery with its characteristic stripes. They typically show up in hard to photograph places, such as those that have near year round snow cover or cloud cover, but we think we even saw some in the Sahara.

Coverage

There are a few locations where non-Landsat imagery has been included in the mosaic. This includes a number of islands, such as Svalbard and the islands in the South China Sea.
Below we can see a particularly noticeable strip across Smith Island, which is part of the Andaman and Nicobar Islands in the Indian Ocean. The image is actually a DigitalGlobe image from 2011 which disappears as you zoom in.

We believe the reason for this is that there simply aren’t any good quality, snow-free and cloud-free Landsat images of the locations in question. Islands, it would appear, are cloud magnets.

Colouring

Overall, the contrast in the imagery is noticeably higher and features you may have never noticed before stand out. Lakes generally seem to be greener or browner than before.

Oceans

It is important to note that the ocean floors are actually a different data set and have not, as far as we know, been updated at this time. However, they did receive a significant update in January this year. We have come across some oddities in the margin between land and sea. For example, along the coast of Vietnam there is a thin border of brown where the Landsat mosaic ends, but between that and the sea floor data is some other imagery which includes some clouds.

We saw this same effect in a number of other locations around the world.

We also found that if you zoom in on Chandler Sound, which is part of the Mississippi delta in the Gulf of Mexico, Google Earth shows this strange pattern:


We are not sure if this has anything to do with the global mosaic update.

Dating the imagery

The imagery is a mosaic collected from parts of images from the Landsat archive going back many years, so it is impossible to put a date on the whole mosaic. However, there are specific places where it is possible to determine the approximate date of the imagery used. The best locations to do this would be large lakes or inland seas that are shrinking or growing over time. We haven’t yet done this for any such lakes, but we did check the Nansen Ice-shelf in Antarctica and determined that the imagery there has not been changed from the previous mosaic. The imagery is from 2003 as we determined when watching the ice sheet crack. We also checked Bento Rodrigues in Brazil and are fairly sure that the imagery is from before the disaster that took place there in December last year

Resolution

Landsat imagery has a resolution of only about 30m per pixel and we suggested yesterday that Google consider using Sentinel imagery, which is higher resolution. However, after some consideration we have realised that for the global mosaic, the important factors are consistent colouring and good global coverage. As you zoom in, Google Earth transitions to higher resolution imagery where available so greater resolution of the global mosaic is not necessary. It is, however, the case that there are some parts of the world where no higher resolution imagery exists and the Landsat imagery is used even when you zoom in and only for these locations does Google need to seek alternative sources. For much of the globe they have already used medium resolution imagery from Spot Image. For more on what image sets are used where, see our series on Google Maps API Maximum Zoom.

To see the locations featured in this post in Google Earth download this KML file.

Filed Under: Site News Tagged With: landsat, pretty earth

Google Earth gets a makeover!

June 28, 2016

Google Earth has just had a makeover. Google has refreshed the global mosaic imagery that you see when zoomed out with newer, better quality imagery. When you zoom in, Google Earth transitions to higher resolution imagery where available, but in places where it is not available, the global mosaic remains. When Google Earth was first released it looked like a patchwork of imagery – essentially the same as it does today when you switch to ‘historical imagery’. Then, in 2012, they released ‘Pretty Earth’ a global mosaic derived from Landsat data which made Google Earth look a lot better. As far as we know, this is the first refresh to the global mosaic since then. The first mosaic was produced using Landsat 7 data. Landsat 7 has faulty instrumentation, which resulted in stripes in the imagery at some locations.

Read more about the new global mosaic on Google’s Lat Long Blog.

Landsat 8 was launched in 2013 and the new mosaic incorporates imagery it has gathered. However, we believe we can still detect, in places, the characteristic stripes of Landsat 7 data, suggesting that the mosaic is not exclusively from Landsat 8.


A location in Venezuela. The squares are roads. The broader, nearly horizontal stripes in the vegetation are almost certainly due to a Landsat 7 image being used.

Also see the Vatnajökull Glacier on Iceland for another location where the Landsat stripes are visible.

Overall, the contrast is higher in the new mosaic and in parts of the US you can see a distinct checkerboard pattern:


The checkerboard pattern is real, being a consequence of the Jefferson Grid.

The mosaic is created by carefully selecting cloud-free and snow-free sections of imagery from the catalogue of Landsat imagery. The resulting, largely cloud-free and snow-free view of the world is actually quite unrealistic. In some cases, such as some mountain ranges and the poles, it has proved impossible to find completely cloud-free, snow-free imagery.


Some clouds are visible in the Falklands.


The northern coast of Greenland hasn’t fared too well with the update, but that is because this is outside of Landsat’s coverage.

Overall, we think the new mosaic is a significant improvement, but without the old one to compare it with, it is difficult to make an accurate comparison.

As far as we know, Sentinel imagery is freely available under similar conditions to the Landsat data. In addition, it is higher resolution than Landsat data. We wonder whether Google has looked into incorporating Sentinel data in the global mosaic.

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

Filed Under: Google Earth News Tagged With: landsat, pretty earth

Google Earth Base Imagery Enhancements

June 27, 2013

Back in January, Google updated the base layer (the layer seen at higher altitudes) of imagery of the Earth to make things more realistic, eliminating the patchwork-like appearance that Google Earth was known for.  The “pretty earth” update made an amazing difference in the overall experience when playing with Earth.  Google has now updated the imagery again and it’s quite a nice improvement!

south_america

This new update is more than just some fresh imagery, though.  Google has worked hard to make it the best they can, as explained in this post on the Google Lat Long Blog:

This stunning new imagery of the earth from space virtually eliminates clouds, includes refreshed imagery for regions of the world where high-resolution imagery is not yet available, and offers a more comprehensive and accurate view of the texture of our planet’s landscape.

Google goes on to make comparisons with NASA’s Blue Marble imagery and shows how they enhanced the Landsat 7 satellite imagery much of it is based on. To see the new imagery for yourself, simply open up Google Earth or Google Maps and zoom out to high altitude.

Filed Under: Google Earth News, Sightseeing Tagged With: pretty earth



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