Systematic errors in ground referenced geometric height monitoring

Abstract

This paper investigates the existence and treatment of systematic errors in geometric height measurement systems. A minimal system of one SSR aided by a low power omni radar equipped with an independent interrogator is taken for reference. Biases are identified to be created by the aircraft transponder and by the nonlinear processing of the available noisy radar range and bearing measurements. The first source is treated by augmenting the estimation process to include the transponder bias. The latter source creates an ‘inherent bias’ which cannot be estimated by augmenting the estimation process. The inherent bias is further analysed by determining the main factors affecting its magnitude. It is shown that the inherent bias limits the useful area in which the geometric height can be reliably estimated. Although the inherent bias investigation method is primarily derived for the SSR-omni measurement system, it can be applied in a straightforward manner to other geometric height monitoring systems employing nonlinear processing of the original measurements.