The Joint Precision Approach and Landing System (JPALS) is a military, all-weather landing system based on real-time, dual-frequency (L1 and L2) local-area differential corrections for GPS signals, augmented with integrity information, and transmitted to the user via secure means. JPALS development started from the civilian LAAS/GBAS system (see above) and split into two separate systems. One of these is known as Local Differential GPS (LDGPS), which is used for airfields on land and includes a variant that can be set up quickly. The other is known as Shipboard Relative GPS (SRGPS), which is used for approaches and landings to ships. Unlike LDGPS, which is more similar to LAAS/GBAS, SRGPS applies a variant of carrier phase differential GPS (CDGPS) to obtain accuracies better than 10 – 20 cm relative to a moving point (or set of points) aboard a ship whose location is included in the information broadcast to airborne users.
Stanford received funding support for JPALS research from the Navy. It investigated the differences between LAAS/GBAS and JPALS to determine what needed to be added to JPALS to meet similar integrity requirements under more difficult conditions, such as increased RF jamming, less time for reference receiver siting, and the motion of both the reference point and the reference receivers in the case of SRGPS. Algorithms developed for LAAS were modified and tested for SRGPS with these complications included. Progress was made in understanding the utility of antenna and sensor-augmentation technologies in counteracting RF jamming, and these results been utilized in Stanford’s ongoing research (see above).
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