A Comprehensive Ionosphere Storm Data Analysis Method to Support LAAS Threat Model Development

Several recent papers have analyzed the potential threat of severe ionosphere spatial gradients on LAAS users [14]. To support this work, a comprehensive methodology has been developed to analyze WAAS Supertruth data as well as both raw and JPL-processed data from the IGS/CORS receiver network to search for anomalous gradients. Anomalous gradients that result from this method are used to populate and validate the LAAS ionosphere spatial gradient "threat model" that is used to determine the potential impact of ionosphere anomalies on LAAS users. This paper explains the ionosphere data analysis method in detail. This method includes two separate chains of analysis. One chain uses dual-frequency (L1 and L2) data that is post-processed by JPL to remove receiver inter-frequency biases as well as obvious receiver glitches. A search for the largest ionosphere spatial gradients (in terms of the apparent gradient "slope" in mm/km) is then performed, and the resulting observations are put through a screening process that confirms that the observed gradients are due to actual ionosphere gradients as opposed to other causes (e.g., incorrect L1-L2 bias estimates; unexplained measurement "jumps"). Surviving observations from this chain are then validated by an analysis of ionosphere rate of change using L1 codeminus-carrier only to insure that the apparent gradients are not due to receiver errors after recovery from loss of lock on L2. Observations confirmed to be due to ionosphere gradients are then analyzed further (using additional nearby receivers) to estimate the gradient width and propagation speed to the extent possible. This paper presents results for analyses conducted using this method for the October 29 30 and November 20, 2003 ionosphere storms over CONUS. These days appear to represent the worst ionosphere storms experienced in CONUS since WAAS and IGS/CORS data became available. Preliminary results for several earlier storms in CONUS that might also be of concern to LAAS are also presented.