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"Google Satellite" To Be Launched This Week
Lord Satri writes "Well, almost. Google signed an exclusivity deal with GeoEye regarding GeoEye-1, the most advanced high-resolution, civil, remote-sensing satellite to date. This must be annoying for other high-resolution, remote-sensing data users since Google already has an exclusivity deal in place with DigitalGlobe, the other major civil satellite imagery provider. From the CNet article: 'Under the deal, Google is the exclusive online mapping site that may use the imagery... in its Google Maps and Google Earth product. And as a little icing on the cake, Google's logo is on the side of the rocket set to launch the 4,300-pound satellite in six days from Vandenberg Air Force Base in California. Terms of the deal weren't disclosed. GeoEye-1 will orbit 423 miles above Earth, but it will be able to gather imagery with details the size of 41 centimeters... Google, though, is permitted to use data only with a resolution of 50 cm because of the terms of GeoEye's license with the US government.'"
Some precisions on my summary. DigitalGlobe is obviously not the only other remote sensing data provider, but it's GeoEye main competitor in civil high-resolution multispectral remote sensing. GeoEye is itself the merging of two other previous major players on the same playing field, OrbImage and Space Imaging.
As for my claim of an agreement between DigitalGlobe and Google, see this two years old entry. The original archive for the DG message is here (the link on /geo does not work anymore).
One of the obvious questions that comes to mind is to which extent these exclusivity deals have negative impacts on other remote sensing imagery customers, small or big.
Another question is; does Google really needs such a deal to provide the best webmapping and virtual globes-related tools?
Animoog.org
It means a car shows up as 4 pixels by 12 pixels. The top of your head is part of a single pixel along with a square foot of sidewalk.
Google already has higher-res data for populated areas of several countries from aircraft reconnaisance. The satellites are for everything else.
Unfortunately, there is a physical limit to how good an image taken from 400 miles away can be.
50cm restriction? do they have something to hide??
For once the government is protecting our pivacy (a side effect of portecting its own, no doubt). 50cm resolution hides the identity and activity of individuals, which is for the best.
Socialism: a lie told by totalitarians and believed by fools.
Google uses aerial photography for the views of major cities - so those 10cm resolution images are not from satellite.
Defining optical resolution from space is a bit tricky, as several generations of optical engineers have discovered.
The main criterion is the telescope's point spread function - this is roughly the angular diameter that a pinpoint star appears to be, as seen through the telescope. We want the smallest point spread function, and it should map onto about one to three sensor pixels. (arguments go here about over/undersampling).
The Fourier Transform of the point spread function is the Optical Transfer Function, which is a graph of the spatial frequencies response of the telescope. It's analogous to a hifi's frequency response ... it's an engineering challenge to prevent high frequencies from getting rolled off.
The main limit for high resolution is the diameter of the primary mirror (All mirrors and optical elements, no matter how perfect, have diffraction effects which spread out the light and reduce resolution. The bigger the entrance pupil, the greater the resolution) For the GeoEye, orbiting at 684Km and a resolution of 0.4m, I roughly calculate the primary mirror is somewhere around a half-meter diameter or so, depending on the wavelength of light it's optimized for.
Other things limit resolution - scattering of light in clear air (Rayleigh scattering) screws up the image, especially in the blue. Dust, haze, clouds and urban pollution are a bother, but not as much as you might think. Naturally, there's lots of image processing software ... quite compute intensive.
A typical human, seen from above and not casting a shadow, is about 20 to 60 cm across. So someone walking down the street should appear on a few (1 to 5) pixels. Not enough to recognize someone, especially since you're looking down on 'em.
Generally, images taken from aircraft have better resolution (they're closer, and there's less Rayleigh scattering). Perhaps airlines will attach automated, downward looking hires cameras to their daily flights.
You spent way, WAY too much time HTMLizing your post. :'(
No, I have a computer from the 'future' First you search google, then you "View source", copy, and paste.