Detailed inherent bias analysis in ground referenced aircraft height monitoring

The authors present the results of an in-depth investigation of the systematic error resulting in aircraft geometric height computations derived by a height monitoring unit consisting of one typical secondary surveillance radar (SSR) and one omnidirectional radar. The systematic error is inherently generated by the nonlinear equation employed to calculate the height from the noisy distance and bearing measurements. Such inherent bias errors are expected in the output of almost every nonlinear system that processes noisy inputs. The inherent bias evaluation is based on a power series expansion which theoretically includes infinite number of terms but in practice has to be truncated at some order. The adequacy of the accuracy achieved with lower order terms is investigated in relation to various geometric factors and noise magnitude combinations