While it is possible to mitigate the impact of ionospheric effects on Global Positioning System (GPS) positioning applications through differential techniques, residual errors may persist in regions of steep TEC gradients. An enhancement of absolute TEC and large‐scale gradients is observed at low latitudes near the equatorial anomaly. This effect is significant in the equinoctial months during periods of solar maximum. In this paper, differential GPS (DGPS) positioning accuracies in the anomaly region are investigated during the period of solar maximum 1999–2000, using as data the L1 pseudoranges. TEC gradients of 30 TECU per 100 km are observed during March 2000, with corresponding horizontal and vertical position errors of approximately 25–30 m (95% confidence level) for single baseline processing. Positioning accuracies are improved by a factor of 5 for a wide area DGPS approach.

No abstract

GPS signals are refracted by the dispersive ionosphere, resulting in ranging errors dependent on both the given signal frequency and ionospheric total electron content. Such range errors translate into a degradation of positioning accuracies. While it is possible to mitigate the impact of ionospheric effects on GPS positioning applications through ionosphere modeling and/or differential techniques (DGPS), residual errors may persist in regions where steep gradients or localized irregularities in electron density exist, particularly during periods of high geomagnetic activity. Such effects are an issue for the reliable implementation of safety‐critical GPS systems. A solar maximum was observed in mid 2000 with associated degradations in GPS positioning accuracies. In this paper the impact of solar maximum on DGPS horizontal positioning applications is investigated. Analyses focus on determining limitations in horizontal positioning accuracies for operational marine DGPS systems. Long‐term analyses are conducted using data from permanent GPS reference networks in Canada, Brazil, and the United States. Several million observations are processed in this study during the years 1998–2000. Studies focus on large ionospheric gradients near the equatorial anomaly and at subauroral latitudes (associated with the main trough and storm‐enhanced densities). Results indicate that DGPS horizontal positioning accuracies are degraded by a factor of 2–5 relative to average values.

No abstract

While designing physical hydraulic model tests to investigate the efficiency of pressure flushing, it is most likely that very fine sediments of cohesive nature are required to satisfy the relevant scaling criteria. Cohesive sediments have different physical properties than sand, and a possibility to avoid such scale effects is to use lightweight materials with a specific gravity larger than water but lower than sand as model sediment. This paper addresses this issue by presenting results from laboratory experiments mimicking pressure flushing through a bottom outlet by using different lightweight materials and sand as model sediments. The results consolidate conclusions of previous studies carried out solely with sand and show that lightweight models can be used to predict the length and volume of flushing cones. Empirical relations to predict the length and volume of flushing cones are proposed and validated against a small set of experimental data from a previous study.