What can you see in satellite photos?

September 30, 2009 10:33 PM

Satellite photos: what interesting features can be seen or measured in them (or other aerial photos), and where can I get a supply of images?

Examples I have already seen, from some crude Google-searching:
Roads
Buildings
Degree of development (urban/suburban/rural)
Oil spills (apparently these are usually hard to see)
Blooms of algae (cyanobacteria) in the Baltic Sea
Damage to buildings from earthquakes

More would be appreciated--the more specific, the better. These will be used in a computer vision system, so I'd especially like to know where I can find a supply of images containing whatever feature I'm looking for (including the above)--easy for buildings or roads, but hard for rare events like oil spills. Natural disasters seem interesting, if there are pictures available.

I would also consider some other kind of non-photographic data as well, if it could be combined with maps or photos. Don't worry whether you think it's suitable; any idea you have will help!

posted by k. to Science & Nature (12 answers total)

Google Earth has a few crop circles in it. Like this one. (They seem to have known when the jet was going to be overhead to photo-survey that area, because the people who did it are laying down just south of it, along with 5 cars and an airplane. Which look to be trying to spell something.)
posted by Chocolate Pickle at 11:26 PM on September 30, 2009

You can purchase hires images of specific areas from commercial earth imaging companies.

GeoEye comes to mind but there are others.
posted by Aegean at 1:11 AM on October 1, 2009

Finding an aircraft in flight is always interesting.

This Lancaster bomber was famous, but the images have changed recently for this spot.

This aircraft has black wings and tail, which made it look like a missile.
posted by trialex at 2:03 AM on October 1, 2009

Don't buy satellite data! Get it for free from the US government! Also with non-satellite information.
posted by tss at 6:18 AM on October 1, 2009

Best answer: I like the Ramona GIS Inventory for navigating to an area in the US and finding out what data is available. It will usually point you in the direction of another database for download. Note that you can define what layers you want to search for. Sounds like you are looking for digital orthoimagery- photographs that are corrected so each pixel represents the image resolution so you can measure spatial characteristics. The National Map http://nationalmap.gov/ is also a good tool, there is a lot of overlap between the two. Note that most areas in the US will have 1 meter resolution aerial orthoimagery available for free thanks to the USDA, called NAIP orthoimagery.

I'll think about where to get imagery for events like oil spills, but no source for orthoimagery immediately comes to mind.

As for cool things a computer vision system could possibly look at...how many lock and dams are on the Mississippi? Is there a relationship between river crossings and nearby population density? What cities have the most athletic fields within their boundaries? I'm sure there are better questions for your system but those sound like they might be fun to investigate.
posted by nowoutside at 6:25 AM on October 1, 2009

Google Sightseeing has a category page that might help you sort through their data more easily.
posted by grateful at 7:13 AM on October 1, 2009

Best answer: The relevant search terms are "aerial photo interpretation," "remote sensing," and "satellite image interpretation." There are entire classes on these. If you have access to a university library, they will no doubt have CDs you can access (though they will probably not be licensed for commercial use).

Computer Vision Research: Automatic Photo-interpretation Systems
posted by desjardins at 7:53 AM on October 1, 2009

Response by poster: Thanks for the suggestions so far. Finding something cool to look at is my main concern; the supply of images is only a problem for rare things like natural disasters (where I would need to get pictures taken at specific dates). Do any other governments have free satellite data?

Note that Google Maps/Google Earth is inconvenient because the pictures can't be downloaded (as far as I know), but I can certainly use it to find things to look at.

According to NASA, Oil spills are notoriously difficult to identify in natural-color (photo-like) satellite images, especially in the open ocean. Because the ocean surface is already so dark blue in these images, the additional darkening or slight color change that results from a spill is usually imperceptible (except in this picture). Also, here's the Jiyyeh power plant oil spill from the Israel-Lebanon war in 2006.
posted by k. at 8:58 AM on October 1, 2009

You can't formally download the images on Google Earth, but it's easy to take screen grabs and extract out the photo part.
posted by Chocolate Pickle at 10:24 AM on October 1, 2009

A lot of my conservation work involves image interpetation. Some of the more obvious natural things one can see in an image include rock outcrops, wetlands, ponds, etc. With some knowledge and practice, one can pick out species of trees.
posted by buttercup at 4:48 PM on October 1, 2009

Try this one - NASA's gateway to Astronaut Photography - not satellite but photos from ISS.
posted by leslies at 6:18 PM on October 1, 2009

When I visited San Francisco in 2005, I noticed that the two towers on the Golden Gate Bridge didn't make the same angle in the "satellite" photo on Google Maps. I did some trigonometry and learned that the photo was taken from 20,000 feet.

In the current photo the difference is much smaller, but still visible in paired screen captures.
posted by fantabulous timewaster at 7:54 AM on October 2, 2009