Thursday, November 5, 2009


In this post, we'll examine using satellite footage as an option.

Some organizations, particularly governmental organizations, may have access to semi- real-time satellite feeds that could potential scan large areas of terrain for the balloon. Computers could scan this imagery for red regions (or, dependency on the resolution, a red pixel!). The  continental US is 3,119,885 square miles, which is a lot to scan.

However, there are a few problems with this approach. We look at a few, in increasing order of importance.

Resolution: Not all satellites have the resolution to resolve 8 ft objects. However, this is certainly within the resolution of modern commercial and spy satellites.

Processing: 3,119,885 square miles is 8.69x10^13 square feet; at a byte per square foot, it's about 86 Terabytes of data for one snapshot of the continental US. Storage and processing-wise, if you have access to satellites with these capabilities, it's not likely to pose huge challenges.

Coverage: Not clear that we have enough satellites to pull in this kind of imagery. This link suggests that one commercial satellite can cover 200,000 square miles per day. The  continental US is 3,119,885 square miles; so optimistically, for a 6 hour period, we are talking about > 60 such satellites. I'm sure someone else who is more of an expert on satellite imagery will be able to comment on this. It's feasible; but obviously only a select group would have access to this kind of resource.

Cloud Cover: As you can see here; cloud cover could well be a problem; at least for identifying all balloons. However, you might be able to get some leads on more clear areas of the US.

False Positives: One issue is; is this balloon actually the balloon we are interested in? Surely there are more than 10 red balloons floating in the US. More on this later. One approach is to diff the image on the contest day from images from previous days. Although this could narrow it down, even if things move a little, there still would be many false positives. More on this issue later.

Conclusion: Satellite footage could potential convey an image to a group correctly positioned; however it would have to be combined with other approaches to handle cloud cover and false positives. It could for instance, be use to confirm reports of a balloon, or to serve as a starting off point for wider social-networking approach. However, the issue of false positives is quite worrisome.

1 comment:

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