Robust sufficient conditions for uniform observability of a linear nonstationary singularly perturbed system

For a linear nonstationary singularly perturbed system with small coefficients of higher derivatives, we examine the property of uniform observability, which characterizes the possibility of uniquely determining the state of the system at any time $t$ by the values of the output function and its derivatives up to a certain order only at the point $t$, as well as the property of approximative observability, which means the possibility of accurate estimating the current state of the system without differentiating the output function using $\delta$-sequences.