Proposing a concept of least-squares-based outlier-exposing potential of Gauss-Markov models: Examples in geodesy

Abstract

Outlier detection and identi_cation are still important issues in the quality control of geodetic networks based on least squares estimation (LSE). In addition to existing network reliability measures, the paper proposes the LSE-based concept (together with the associated measures) of the Outlier-Exposing Potential (OEP) for Gauss-Markov models. The greater the model’s redundancy, the more the con_guration of its responses to gross errors exposes the location of these errors, and hence, the greater the model’s OEP. The potential is given in the basic version and the extended version. The former considers only the e_ect of the model’s redundancy, while the latter also considers the masking e_ect due to random observation errors at a speci_ed magnitude of gross error. For models that have regions of unidenti_able errors, the corresponding OEP components have zero values. The re_ection of OEP in the values of Minimal Identi_able Bias (MIB) is shown. It is proposed that OEP derived based on least squares adjustment be treated as a property of the model itself. The theory is illustrated on several 1D and 2D networks. The research is limited to models with uncorrelated observations and the case of a single gross error. These limitations enabled the formulation of clear properties of general character, not complicated by observation correlations and multiple-outlier combinations.

Keywords

• least-squares adjustment
• uncorrelated observations
• redundancy matrix
• disturbance/response relationship
• response concentration index