1. An observation system configured to observe one or more initially unknown state variables of an observed system, comprising: an input interface configured to receive a system input; and a processing module coupled to the input interface; wherein the processing module is configured to determine the one or more initially unknown state variables; and the processing module is configured to perform the determination based at least in part on the system input, a plurality of known state variables, and a time varying mode vector {tilde over (G)} n that is time dependent, wherein n is a time step and a value of n corresponds to a sequence of integers.