Monitoring and correction of SSR product errors using PPP float ambiguity deviations and phase residuals

Errors and anomalies in real-time State Space Representation (SSR) products can substantially degrade the performance of precise point positioning with ambiguity resolution (PPP-AR). The existing network-based monitoring approaches mainly rely on phase residuals to detect SSR product errors. These methods perform effectively when monitoring stations achieve integer ambiguity resolution, as product errors are then fully expressed in phase residuals. However, for SSR products with ambiguities not fixed, a portion of the product error is absorbed in the float ambiguity estimates while only the remainder manifests in phase residuals. This incomplete error representation prevents reliable assessment, typically leading to the exclusion of these SSR products from service. Such exclusion reduces SSR product availability and can compromise PPP-AR performance in challenging scenarios, where maintaining service continuity is critical. To overcome this issue, this study presents a monitoring and correction framework applicable to SSR products regardless of their ability to support ambiguity resolution. The approach recognizes that product errors in float PPP processing separate into two quantifiable components. The first component is absorbed by float ambiguity parameters and revealed through deviations between estimated ambiguities and their integer values. The second component persists in phase residuals. Extracting and jointly considering both components enables complete error characterization independent of whether ambiguities can be subsequently fixed. The method operates through coordinated processing at multiple monitoring stations. First, the float PPP solutions yield ambiguity deviations and phase residuals for each tracked satellite. These ambiguity deviations exhibit spatial correlation across the monitoring network. Then, wide-area modeling exploits this correlation to estimate systematic and spatially coherent error corrections in the SSR products. The resulting corrections mitigate these error components, after which phase residuals predominantly represent random, uncorrectable errors suitable for anomaly detection and quality evaluation. The experimental validation using real-time SSR products provided by the Centre National d’Études Spatiales (CNES) and wide-area monitoring stations in China demonstrates that the proposed method effectively improves the reliability and availability of SSR products, while significantly enhancing ambiguity resolution robustness and positioning performance in real-time PPP-AR applications.  Compared with phase observation residual-based and no-monitoring methods, the proposed method reduces incorrect ambiguity fixing rates by 0.47% and 4.22%, and three-dimensional positioning errors by 71.7% and 82.2%, respectively.