# Meters per square root hertz [closed]

Looking at some ESA papers I found an unit that I don't know, picometers per square root hertz.

Anybody could tell me what this unit is for?

Thanks!

• I would personally appreciate more context, e.g. a link to the paper in question. – Dzarda Jul 20 '15 at 9:51
• It'd help a lot if you provided context of where you found this unit. Just "ESA paper" is very vague. – Curd Jul 20 '15 at 9:52
• And what is ESA? European Space Agency or what? More context, please! – Lorenzo Donati supports Monica Jul 20 '15 at 9:54

• No, the picometers does not refer to wavelength. The instrument is ultimately measuring the displacement of some masses that is caused by gravity waves, so naturally, the unit of measurement is length -- picometers, in this case. And the frequency in $\sqrt{Hz}$ is not the absolute frequency, but rather the bandwidth of the measurement. Noise power (for white noise) is directly proportional to bandwidth, and power is proportional to the square of the amplitude, so the noise amplitude (voltage, current, displacement, etc.) is proportional to the square root of the bandwidth. – Dave Tweed Jul 20 '15 at 11:43