5/3/2005: Korea at night

[spanishguy]

I have spent probably too much of my time looking at satellite imagery from nasa. One thing that is certain is that the same location can look very different depending on a huge number of variables. This image did look a bit extreme based on other images I have seen. I took this one in to Photoshop and started playing with levels and correction. Here are some results.

<img src="http://home.cwru.edu/~tje2/korea-lights-analysis1.jpg">

I noticed there was a definite difference in the ocean brightness from left to right. pumping up the brightness and contrast brings this out more in the second image. The last image is 'corrected' by myself, eyeballing a line and trying to get the water to the same, consistent brightness. Pyongyang seems to show up much better and this image fits in more with others I have seen. Up in China, however, I think the lighting patterns are not so much cities as they are mountains or geographic features reflecting some sunlight.

<img src="http://home.cwru.edu/~tje2/obvious.jpg">

In the image above, I used the uncorrected version and only played with levels of brightness and contrast in order to really bring out the left-right differences in the image. It plainly shows that the image is not consistent from left to right, regardless of land mass or city lights.

<img src="http://home.cwru.edu/~tje2/contrasty.jpg">

This last image is a left-right corrected version in which I tried to get the lights to show up in a manner used in the other composites people are posting. It still is a bit inconsistent, and very grainy. It is closer to the other images, but quite frankly the image quality is too low and the overall calibration is too inconsistent to really make inferences about North Korea's light levels vs. levels in other parts of the image.

The popular Visible Earth composites are made from thousands of different images laced together. Average brightness for different areas are plotted from multiple observations. A single image is bound to contain inconsistencies, and should not be used directly without context. I'm sure the person who saw this and emailed it around just saw something that helped reinforce a preconceived notion about Korea's situation. Careful analysis shows that while there is a major difference, this image seems to exaggerate the light discrepancy.


There are other factors we haven't even touched - does North Korea use mostly sodium, metal halide, halogen, incandescent, or florescent lighting? At what wavelength is the picture taken? What time was it taken? Were there clouds? Snow? Dust storms? Was this a holiday in North or South Korea? Friday night football games? Tax day? Certainly, some of these are ridiculous questions, but taking a small number of pictures and making broad inferences is always dangerous. You ALWAYS will see things that seem to reinforce preconceived notions. Just ask Colin Powell.