Google Earth Imagery
You will be surprised to know the number of people thinking that Google Earth displays imagery in real time. On the other hand, the images are only a day old. Many people today watch weather satellite photos on television that are only few hours old. But there are many problems to obtain high resolution imagery. Weather satellites are at a distance of 36000 kms taking geosynchronous orbits.
High resolution satellites operate only a few hundred kms above the earth. That means they are able to view only a small part of the planet with their camera. Every 90 minutes these satellites move around the planet but they cover only about 1 percent of the globe on each pass. Imagery of Google Earth is at its best when there are few or no clouds, or when there is little pollution/haze.
Once the images are taken, commercial providers take some time for processing the data before it is finally made available to customers. Google Company is one such customer. Google evaluates the new imagery taking the current imagery into account to decide whether the new imagery has better resolution than the current. This may take, quite a bit of time depending upon the quantity of landmass it is processing. To speed up the process, Google has decided to automate this process.
When the image is chosen, it is processed into a format that is supported by coordinate system of the Google Earth's databases. It then goes through the control process before it is finally distributed Google Earth database servers. That is why in Google Earth, you will not get any imagery that is younger than 6 months. And why updates happen once in every 60 days.
Google Earth imagery not only comes from satellites but also from aerial photographers. These photographers mostly in airplanes have special very high resolution cameras. Imagery is also provided to Google by state or city governments. Age of imagery varies considerably but mostly high resolution images are 6 months to 5 years old.
As the imagery is taken from different sources, the process of getting imagery into the software application (Google Earth) is complex, hence may take a considerable amount of time. Companies also have to spend a lot of money to get the latest quality imagery. More recent images are valuable than older images. That is why these companies are a bit reluctant to make newest imagery available for anyone without charging anything.
However, near real time images of Earth are available on Google Earth. There is the new clouds layer. It is under ‘new Weather layer' folder. Weather satellites actually take the images of the clouds. These represent a global picture of clouds and are 2-3 hours old. Thus using Google Earth, you will be able to view recent weather updates. Before using imagery from Google Earth for business applications, very carefully read the rules and conditions for using Google Earth imagery. You cannot sell or use Google Earth imagery for business purposes, unless you have taken prior permission.
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