This paper discusses the resistance of gross errors with quasi accurate detection and the improvement of ill conditioned equation with ridge estimate when the equation is ill conditioned and polluted.

This algorithm, which first solves target's altitude and avoids ill-conditioned system of equation, can improve the location accuracy with the same operating complexity.

When the least square criterion is applied to the state estimation of a large scale power system, high order of the equation will make it ill-conditioned.