If you were living in the States, you would have been amongst the first to see your
house picture satellite
photo online. Before Google Earth and the other modern internet satellite photo services, seeing your house on a satellite photo was a novel and thrilling thing.
The image on the right, obtained when this page was first published in 2003, was state-of-the-art, as far as the internet was concerned. Here you can see the Golden Gate Bridge, from the California maps and could see individual cars. The resolution was astounding for its day.
Now, Google Earth
software and the online version at http://maps.google.com/ provides maps for anywhere in the world and has done so since 2005.
Prior to this, satellite imagery was used for meteorology and other specialty purposes, rather than for fun and the production of everyday commercial maps. To make the details visible on the earth picture, satellite technology required what was then an unimaginable number of pixels. Probably more than all the weather satellites combined, but who knows for sure?
What is a Pixel?
A tiny point of light serving as the smallest unit used in constructing a video image. Just like on your computer screen.
The word breaks down to picture element, where pix is short for pictures.
The house picture satellite example above uses very small sized digital camera pixels compared to the weather
equipment described in the paragraphs that follow.
Weather satellite produce video images as well. And that requires enormous data resources. And with ever-increasing resolutions the amount of data keeps growing exponentially. The basic physics is still the same today.
Each pixel on a weather satellite display still shows a representative temperature (or other variable) for quite a large area of the planet below. And, though not fine enough to make out your house picture satellite depictions from these weather devices work very well for large items such as synoptic systems and weather. Plus they can distinguish a few smaller features.
A lake, cloud or snow patch for example which is smaller than the pixel will likely change the colour of the entire block slightly, but that is about all. Larger items spanning two or more pixels show up more easily.
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Special duty: This is where the concentration of data comes in to play. Resolution
defines the limit of the detail available in any recording, video, audio
or otherwise. It can be expressed in scale units such as inch to
pixels or kilometres per pixel.
Small objects cannot be resolved, and to see something as little as satellite equipment needs to be specifically designed for this purpose.
Satellite resolution fluctuates substantially. For geostationary equipment thousands of miles above the earth, visible light spectrum wavelengths give the best resolution. The horizontal resolution of a single pixel from a GEOS stationary satellite positioned over 22 thousand miles above the earth is about a thousand metres square on the equator directly below the satellite vehicle.
This minimum size will increase to double its size, or half the
resolution, for more distant points on the earth (such as towards the poles). The camera device can
about as far as approximately 70-degree latitude, both north and south.
The IR infrared and water vapour resolutions use longer wavelengths and have poorer resolutions - eight and fourteen times worse than visible spectrums respectively. But they still provide valuable information. Because they provide information of a different class.
The NOAA polar orbiting satellites fly much closer to the planet. They have better resolutions because of this. Their squares are more like 1 km for all wavelength channels. The house picture satellite imagery shown above uses U.S. Geological Survey data rather than NOAA satellite images. And the satellites providing imagery to Google, Bing and so forth are even better. Plus they provide colour photography.
Have a look at the NOAA satellite images main page here.
An average home measures about 20 meters long. To clearly see this, satellite pixels need to be less than this size, much smaller than what the current weather satellites use.
As photographic resolutions continue to improve and data storage and transfer keeps becoming cheaper, this technology will keep getting better.
To show you your house picture, satellite photos need to provide detail from well above the air.
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Other things to check on
Stuff in the Air:
It's called Blowin' in the Wind.
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