digitalglobe

You hear people refer to the “Google satellites” from time to time when discussing Google Earth and Google Maps. In truth, Google doesn’t have any satellites up in space to capture imagery. While they capture imagery via planes and cars (and even boats, trains and snowmobiles, the satellite imagery is purchased by Google from large providers such as DigitalGlobe and GeoEye.

These satellites operate just a few hundred kilometers above the Earth. This means they only see a small part of the Earth with their camera as they orbit over. They typically go around the Earth every 90 minutes, but only cover about 1% of the Earth on each pass – but, most of the area covered in a pass is water. Not only that, but imagery for Google Earth is only going to be good if the sun is at a high angle when the satellite goes over (fewer shadows), when there are no clouds, and as little haze/pollution as possible. Believe it or not, the times when these factors all come together are pretty rare.
Once the imagery is taken, it takes time to process the data before it is available to customers. Google is one of these customers (a really big one). Google has to evaluate the new imagery against the current imagery to determine whether the new is better than the current. I assume they are trying to automate as much of this as possible. But, for important areas with large populations the process most likely involves people. This process takes time – especially when you think about the quantities of land mass of the Earth. Once an image is selected, it has to be processed into the format and coordinate system of Google Earth’s databases. Then it has to go through a quality control process and fed into a processing system before it gets distributed to the live Google Earth database servers. This is one reason why you usually do not find any imagery younger than about 3 months in Google Earth and why updates only happen about once every 30 days.
For more about how Google Earth imagery is captured and processed, you can read this excellent post that Frank wrote a few years ago.

A few weeks ago, we showed you how France had tried to hide the location of a nuclear plant, after that plant made news after a minor explosion. We showed you how it was hidden in Google Earth by their imagery provider, but was clearly visible by using historical imagery.
A similar situation has just come up in Sweden. Stefan at Ogle Earth has written a great summary of the story, but it goes something like this:
• Some of their “military secrets” are visible on Google Earth, but not on their local mapping sites (Hitta.se and Eniro.se).
• Google uses imagery from Lantmäteriet to cover parts of the country, and Lantmäteriet sensors some sensitive areas.
• There are two main underground control centers for Sweden’s air force; one is visible in Google Earth, the other isn’t.
• The one that is visible is because Google is using imagery from DigitalGlobe for that part of the country, and they’re not censoring it.
Stefan goes on to point out something even more interesting — historical imagery of the obscured area from a few years ago clearly reveals the facility, and the imagery was also from Lantmäteriet; they just weren’t obscuring it yet!
The bigger problem is the method of how the imagery is being obscured. In many cases, such as the Netherlands and the French nuclear plant we mentioned above, imagery is simply blurred to hide details of the buildings, like this (KML):

In the case of Sweden, they modify the imagery to look like fields and forests. While this could potentially help hide their secrets more effectively, it also puts into question the accuracy of all of their imagery.
Stefan shows the example of the village of Hästveda, seen below before and after the photoshopping that removed it from their imagery.

As I asked last time, is it becoming futile to try to hide imagery like this? Or should they keep pressing on in order to try to prevent people from discovering the location of sensitive areas?