Incorporating WAAS Data Into an Ionospheric Model for Correcting Satellite Radar Observations

The GPS Real-Time Ionospheric Monitoring System (GRIMS) has been operational at the Millstone Hill radar in Massachusetts since 1991 and at the FPS-85 radar in Florida since 1994. GRIMS employs GPS derived estimates of the total electron content (TEC) to provide real-time ionospheric corrections to radar measurements, incorporating data from a single receiver to generate TEC estimates for the entire visible sky. Comparisons with range residuals on laser calibration spheres have shown that the GRIMS ionospheric model degenerates during times of sharp spatial TEC gradients, e.g. during geomagnetic storms and day/night transitions. To render the system more robust, we upgraded to a new GPS receiver capable of decoding the signal from the FAA’s Wide Area Augmentation System (WAAS). The WAAS signal, culled from over 25 ground reference stations, communicates the vertical ionospheric delays and the associated confidence bounds at grid points regularly spaced in longitude and latitude. Preliminary results suggest that the WAAS model compares favorably to the model currently employed by GRIMS; the improvement in the radar metric data is verified via range residuals on calibration satellites.