Ionospheric amplitude scintillation is particularly common in equatorial and low-latitude regions, affecting the performance of GNSS precise positioning services. \(\:{S}_{4c}\) index derived from carrier-to-noise ratio data released by the geodetic GNSS receivers can be used to monitor ionospheric amplitude scintillation. However, this index is susceptible to GNSS receiver background noise like the observation noise and multipath effect, especially in low elevation angle conditions, which can result in misjudgment of scintillation event. In this study, by suppressing the GNSS receiver background noise using the method of de-mean and adaptive weight coefficient adjustment, we propose an improved amplitude scintillation index as \(\:{IS}_{4c}\) based on \(\:{S}_{4c}\) . Experiments using the data derived from Ionospheric Scintillation Monitoring Receiver (ISMR) in Hainan of China show that the average of misjudgment rates of ionospheric scintillation for \(\:{IS}_{4c}\) and \(\:{S}_{4c}\) are 3.7% and 11.7%, respectively, and the improvement rate of \(\:{IS}_{4c}\) over \(\:{S}_{4c}\) is 69.9% in 2023. Further experiments using consecutive 30 days data in 2023 from 20 GNSS stations equipped with four mainstream geodetic receivers (JAVAD, LEICA, SEPTENTRIO, and TRIMBLE) indicate that the average improvement rates of \(\:{IS}_{4c}\) over \(\:{S}_{4c}\) for the four receivers are 63.6%, 69.2%, 61.3%, and 61.4%, respectively. Meanwhile, two-dimensional \(\:{IS}_{4c}\) maps generated by GPS L1 signals data collected at 1363 stations in the range of 45°S-45°N and 60°E-180°E during the Tonga volcanic eruption on January 15, 2022 show better ionospheric scintillation monitoring performance than those of \(\:{S}_{4c}\) . In addition, we also applied the \(\:{IS}_{4c}\) in the construction of the Improved Receiver Tracking Error Stochastic (Impr_RTES) model for GPS Precise Point Positioning (PPP). Experiment results indicate that compared with the Elevation Angle Stochastic (EAS) model, the Impr_RTES of \(\:{IS}_{4c}\:\) can improve the positioning accuracy of PPP by 15.5%, 26.3%, and 36.2% in the east, north, and up directions, respectively.
