In experimental physics, we often make measurements of linear transfer functions; these are complex-valued functions of frequency. If the underlying system is causal, then the transfer function must be analytic, satisfying the [Kramers-Kronig](http://en.wikipedia.org/wiki/Kramers%E2%80%93Kronig_relation) relations. Our measurements, however, are corrupted by random (and perhaps systematic) errors.

**Is it possible to improve a measurement of a linear transfer function of a causal system in the presence of noise by applying some kind of constraints derived from the Kramers-Kronig relations?**