1. A method for advanced condition monitoring of an asset system, the method comprising the steps of: segmenting an operational envelope of an asset system into a plurality of operating regimes; sensing actual values of an operating condition for one of the plurality of operating regimes of the asset system using at least one sensor; estimating sensed values of the operating condition by using an auto-associative neural network (AANN) of the actual values sensed by the at least one sensor; determining a residual vector between the estimated sensed values and the actual values sensed by the at least one sensor; performing a fault diagnostic on the residual vector; and providing an alert if a change of the operation of the asset system has been determined.