View Full Version : Speculative Satellite Image Observations
02-18-2011, 07:43 AM
I was reviewing a lot of the satellite pictures and aircraft pictures that people have linked in this sub forum and I began to feel lost in the enormous scope of them. The pictures capture such large areas that it is difficult to understand what you are seeing, so I look for human constructions to understand the size of things but cannot seem to find much that is useful. Human beings have built these enormous cities that span miles and miles of ground, yet when you take a look at these pictures that show mountain ranges and coast lines they seem to not even be there at all. Yet I am convinced somehow their effect on the geography must be there. Maybe it is a slight shift in color or the absence of one. Maybe it is dirty water or smog? There must be something. To understand this I think I just need to find a really good map with exceptionally high resolution.
Also, contrary to what I thought I knew, it seems that most rivers when viewed from a great distance away are not any kind of blue color, but are somewhere between a brown or a green. Maybe the reason for this is that rivers themselves are rarely visible from great distances, but what is more visible is their effects on the surrounding land.
To search for the images I seek I have been using Google's image search engine and filtered out all images less than 70 MB - although it doesn't seem to really do this since most of the results are around 10 MB. Ideally I think I would like to see detail 10 times this, and I think my computer and internet connection could handle this. I just don't know how I am supposed to find a +100 MB satellite picture of the North American coastline or something similar. Anyone have any ideas?
02-18-2011, 02:35 PM
Set Google Maps to satellite mode, or download Google Earth. That should get you 90% of the way to where you want to go. Or, you could take a look for scientific satellite imagery. You have to jump through a few hoops and really know exactly what you want, but you can get some really nice data that way. I got heightfield imagery of the Nazca plateau in Peru from down to a resolution of 30m per pixel, which is pretty good for South American imagery. That came from a Japanese satellite called ASTER.
As regards rivers, you're right—they do usually appear brown or green thanks to the vegetation that grows along their banks and the silt they are usually carrying. Even up close, you don't often see a river that reflects the sky well enough to really be blue. But in terms of a map, the expectation is that blue = water, so even though that's not really what it looks like, people color their rivers blue anyway. I tried to get away with a green-brown river on a map, and everyone who offered an opinion said it looked wrong.
02-18-2011, 03:10 PM
Yes, water is one of those things which has a reflection which varies depending on the angle you view it at. At shallow angles like you get when stood on the bank it picks up a significant amount of sky. When viewed from above then you see deeper into it and it looks a lot darker. The sea is naturally a blue / green as well as that from the sky so any light which does go into the sea and reflects back from particles will appear with a blue green tint to it. Fresh water is less like that tho and I think just more clear in nature so it just steadily goes to black as it gets deep. I am less sure about this tho.
If you want high res pics of coastline thats not the US but are 100Mb is size then the ones from Linz in new zealand are a good start:
click on the coloured squares on the map:
Don't try to look at the full res ones in a browser - 200Mb TIFF is gonna kill it. You need to right click download them. Even the JPGs are pretty huge as well. But these are great reference pictures and they have a reasonable usage policy for them.
02-19-2011, 12:34 AM
If you're interested in more detailed pictures, you might want to check out NASA's Earth Observatory (http://earthobservatory.nasa.gov/). The pictures often focus in on an area. For example, the current picture of the day is Sandy Neck, Cape Cod, Massachusetts (http://earthobservatory.nasa.gov/IOTD/view.php?id=49341) It's only a 2Meg file but the roads are clearly visible.
02-19-2011, 01:00 AM
One of the reasons that the effects of people aren't so visible from high up is that people like to grow vegetation above their heads. Most city suburbs, for example, are pretty much just open woodlands with buildings under the trees. The most obvious human effects are effects on waterways, specifically in the form of dams and their associated reservoirs. There are also examples of bodies of water that just aren't there anymore (Lake Chad in Africa and the Aral Sea in Asia are two examples). There is also usually a pall of smoke and pollution over much of mainland China and often northern India.
If you really want to see the effects of humanity on the planet, look at the darkside imagery. Google maps has a nighttime view ( http://www.cc.gatech.edu/~pesti/night/ ) that shows the impact that people have (and lighting at night roughly correlates with wealth).
Another major visible effect of humanity is fires. We like to set them and put them out. http://rapidfire.sci.gsfc.nasa.gov/ has good fire maps worldwide and also provides daily worldwide satellite imagery down to about 250 meters (which is just about where small clusters of human artifacts start to become visible).
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