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by ahofmann 629 days ago
A commercial venture can observe movements in the millimeter range from space? If this is true, I'm equally impressed as I'm terrified.
3 comments

In some conditions, yes. You need a cluster of points which have good reflectivity and coherence properties to microwaves over some time (months to years). Manmade steel and concrete structures, like bridges, houses, dams, etc, usually work very well.

You can't measure their position to the millimeter range, but with some interferometry techniques you can measure their movement to the millimiter range, relative to close points. Some variation of https://www.sciencedirect.com/science/article/pii/S092427161... was likely used in that work, I've seen it done for many other structures (and I even tried to setup a pipeline for doing that for commercial customers, but in the end we didn't manage anybody to fund us).

You can probably get better measurements with an onsite survey, but using satellite data has the advantage that with a handful of satellites you can map an entire country once every one or two week, and after throwing some computing power at it you can theoretically monitor all the bridges and houses at once and get early predictors of possible problems.

These case studies give you a hint of what can be done: https://www.sarproz.com/case-studies/ (I'm not and never have been affiliated with that product, just linking some cool pages).

For a advanced course of physics, we had to analyze video image of tiny "balls" in a microscope and track their movement. We were able to track movements of 1/10 of a pixel fitting a function using the tones of grey. Even if a pixel is 10 meters, I think it's possible to track smaller changes assuming the bridge does not change the shape too much.
You absolutely can and it is true.