Exactly. The imprecision of the mirror surface (and various other optical surfaces in the system) cause their own interference pattern that can be measured and subtracted from the recorded signal.
Even so, measuring gravity waves requires ridiculous amounts of precision in the construction of the interferometer. I'm working at the 10^-6 scale, where optics can still be adjusted by hand. They are working at the 10^-21 scale - the sheer engineering challenge is awe-inspiring.
Even so, measuring gravity waves requires ridiculous amounts of precision in the construction of the interferometer. I'm working at the 10^-6 scale, where optics can still be adjusted by hand. They are working at the 10^-21 scale - the sheer engineering challenge is awe-inspiring.