Jiyun Lee

The ionosphere has been the most challenging source of error to mitigate within the community of global navigation satellite system (GNSS)-based safety-critical systems. Users of those systems should be assured that the difference between an unknown true position and a system-derived position estimate is bounded with an extremely high degree of confidence. One of the major concerns for meeting this requirement, known as integrity, is ionosphere-induced error or discontinuity of GNSS signals sign

Ground-based augmentations of the global positioning system demand guaranteed integrity to support aircraft precision approach and landing navigation. To quantitatively evaluate navigation integrity, an aircraft computes vertical and lateral protection levels as position-error bounds using the standard deviation of ionosphere spatial decorrelation. Thus, it is necessary to estimate typical ionospheric gradients for nominal days and to determine an appropriate upper bound to sufficiently cover th

Large spatial variations in ionospheric delay of Global Navigation Satellite System signals observed during severe ionospheric storms pose potential threats to the integrity of the Ground-Based Augmentation System, which supports aircraft precision approaches and landing. Range-domain monitoring within the Ground-Based Augmentation System ground facility cannot completely eliminate all possible ionospheric threats, because ionospheric gradients are not observable to the ground monitor if they im

Due to their weak received signal power, Global Positioning System (GPS) signals are vulnerable to radio frequency interference. Adaptive beam and null steering of the gain pattern of a GPS antenna array can significantly increase the resistance of GPS sensors to signal interference and jamming. Since adaptive array processing requires intensive computational power, beamsteering GPS receivers were usually implemented using hardware such as field-programmable gate arrays (FPGAs). However, a softw

All fault modes in the Local Area Augmentation System should be mitigated within the specified integrity risk allocation to guarantee the safety of a landing aircraft. However, monitoring within the LAAS Ground Facility is insufficient to completely protect users from unacceptable errors due to ionosphere spatial gradient anomalies. A methodology has been developed to inflate the broadcast σpr_gnd and σvig so that subset satellite geometries (i.e., subsets of the set of approved GPS satellites f

Global Navigation Satellite Systems (GNSS) are now recognized as cost-effective tools for ionospheric studies by providing the global coverage through worldwide networks of GNSS stations. While GNSS networks continue to expand to improve the observability of the ionosphere, the amount of poor quality GNSS observation data is also increasing and the use of poor-quality GNSS data degrades the accuracy of ionospheric measurements. This paper develops a comprehensive method to determine the quality

ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. To quantitatively evaluate navigation integrity, an aircraft computes vertical and lateral protection levels as position-error bounds using integrity parameters broadcast by a nearby LAAS Ground Facility (LGF). These parameters include a standard deviation of ionosphere spatial decorrelation because the range errors introduced by the ionosphere vary betwee

Abstract Deep signal fading due to ionospheric scintillation severely impacts global navigation satellite system (GNSS)‐based applications. GNSS receivers run the risk of signal loss under deep fading, which directly leads to a significant decrease in navigation availability. The impact of scintillation on GNSS‐based applications can be mitigated via dual‐frequency signals which provide a backup channel. However, the benefit of dual‐frequency diversity highly depends on the correlation of fading

Extreme ionospheric anomalies occurring during severe ionospheric activity can pose an integrity threat to users of Global Navigation Satellite System (GNSS) Ground Based Augmentation Systems (GBAS). While most very large spatial gradients in slant ionospheric delay were observed on high‐elevation satellites, several extreme gradients were also observed on satellites below 15 degrees elevation. This paper details the study of anomalous ionospheric spatial gradients for low‐elevation satellites o

The local area augmentation system (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing navigation with guaranteed integrity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category II and III operations. The primary concern has been the need to guarantee compliance with stringent requirements for navigation availability. This paper describes h

Abstract Responding to the ever-growing demand for environmental information, the National Oceanic and Atmospheric Administration (NOAA) seeks to enter into contracts to purchase Global Navigation Satellite System (GNSS) radio occultation (RO) observations produced by commercial vendors at a low-cost. GeoOptics is one commercial vendor awarded a contract with NOAA. GeoOptics operates the Community Initiative for Cellular Earth Remote Observation (CICERO) constellation of low-earth-orbiting (LEO)

The Brazil ionospheric study project aims to develop a new ground-based augmentation system (GBAS) ionospheric threat model to better reflect Brazil's low-latitude conditions. Data processing from the global navigation satellite system for 123 active ionospheric days identified 1017 anomalous ionospheric gradients caused by nighttime equatorial plasma bubbles (EPBs). A significant number of gradients, including the largest verified gradient of 850.7 mm/km, exceed the upper bound (375–425 mm/km)

Extreme medium-scale traveling ionospheric disturbances (MSTIDs) occurred at midlatitudes in East Asia during a geomagnetically active time on 10 November 2004. Using the Global Positioning System (GPS) observation data from Korean GPS reference stations, the characteristics of the MSTIDs on 10 November 2004 and their potential impact on GPS-based navigation systems in the Korean region are analyzed. The MSTIDs were first observed in the northeast part of South Korea at about 10:00 UT and propag

Differential global navigation satellite systems (GNSS)-based aircraft precision approach and landing systems require the development of ionospheric threat models to insure that users are sufficiently protected against ionospheric anomalies. The long-term ionospheric anomaly monitor (LTIAM) is being used to build ionospheric threat models for ground-based augmentation systems (GBAS) and to continuously monitor ionospheric behavior over the life cycle of GBAS. While LTAIM exhaustively detects all