Observability for Non-autonomous Systems

TL;DR

This paper establishes observability estimates for non-autonomous systems with time-varying operators, providing conditions under which the system's initial state can be inferred from observations over measurable time sets.

Contribution

It introduces a novel abstract framework for observability in non-autonomous systems and applies it to elliptic and Ornstein-Uhlenbeck operators with geometric conditions.

Findings

Proves final-state observability estimates using an uncertainty principle and dissipation estimate.

Derives necessary and sufficient geometric conditions for observability in elliptic operators.

Extends results to non-autonomous Ornstein-Uhlenbeck operators with spatial observations.

Abstract

We study non-autonomous observation systems \begin{align*} \dot{x}(t) = A(t) x(t),\quad y(t) = C(t) x(t),\quad x(0) = x_0\in X, \end{align*} where $(A(t))$ is a strongly measurable family of closed operators on a Banach space $X$ and $(C(t))$ is a family of bounded observation operators from $X$ to a Banach space $Y$. Based on an abstract uncertainty principle and a dissipation estimate, we prove that the observation system satisfies a final-state observability estimate in $\mathrm{L}^r(E; Y)$ for measurable subsets $E \subseteq [0,T], T > 0$. We present applications of the above result to families $(A(t))$ of uniformly strongly elliptic differential operators as well as non-autonomous Ornstein-Uhlenbeck operators $P(t)$ on $\mathrm{L}^p(\mathbb{R}^d)$ with observation operators $C(t)u = u|_{\Omega(t)}$. In the setting of non-autonomous strongly elliptic operators, we derive necessary and sufficient geometric conditions on the family of sets $(\Omega(t))$ such that the corresponding observation system satisfies a final-state observability estimate.