2011
Lee, Jiyun, Seo, Jiwon, Park, Young Shin, Pullen, Sam, Enge, Per
Ionospheric Threat Mitigation by Geometry Screening in Ground-Based Augmentation Systems Journal Article
In: Journal of Aircraft, vol. 48, no. 4, pp. 1422-1433, 2011.
@article{Lee2011c,
title = {Ionospheric Threat Mitigation by Geometry Screening in Ground-Based Augmentation Systems},
author = {Jiyun Lee and Jiwon Seo and Young Shin Park and Sam Pullen and Per Enge},
doi = {10.2514/1.C031309},
year = {2011},
date = {2011-07-01},
journal = {Journal of Aircraft},
volume = {48},
number = {4},
pages = {1422-1433},
abstract = {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 impact the satellite-to-ground lines of sight with the worst-possible geometry and velocity. This paper proposes an algorithm called position-domain geometry screening to remove potentially hazardous satellite geometries under worst-case ionospheric conditions. This is done by inflating one or more integrity parameters broadcast by the ground facility. Hence, the integrity of the system can be guaranteed without any modification of existing avionics. This paper develops an algorithm that allows the ground station to conservatively estimate the worst-case ionospheric errors for Ground-Based Augmentation System users. The results of this algorithm determine which potential aircraft satellite geometries are safe and which are unsafe, and inflation of the broadcast vig parameter is used to make all unsafe geometries unusable for the Ground-Based Augmentation System. Although the elimination of unsafe geometries reduces system availability, this paper shows that acceptable availability for category I precision approaches is attainable at Memphis International Airport and Newark Liberty International Airport while guaranteeing system integrity under anomalous ionospheric gradients.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 impact the satellite-to-ground lines of sight with the worst-possible geometry and velocity. This paper proposes an algorithm called position-domain geometry screening to remove potentially hazardous satellite geometries under worst-case ionospheric conditions. This is done by inflating one or more integrity parameters broadcast by the ground facility. Hence, the integrity of the system can be guaranteed without any modification of existing avionics. This paper develops an algorithm that allows the ground station to conservatively estimate the worst-case ionospheric errors for Ground-Based Augmentation System users. The results of this algorithm determine which potential aircraft satellite geometries are safe and which are unsafe, and inflation of the broadcast vig parameter is used to make all unsafe geometries unusable for the Ground-Based Augmentation System. Although the elimination of unsafe geometries reduces system availability, this paper shows that acceptable availability for category I precision approaches is attainable at Memphis International Airport and Newark Liberty International Airport while guaranteeing system integrity under anomalous ionospheric gradients.
2010
Datta-Barua, Seebany, Lee, Jiyun, Pullen, Sam, Luo, Ming, Ene, Alexandru, Qiu, Di, Zhang, Godwin, Enge, Per
Ionospheric Threat Parameterization for Local Area Global-Positioning-System-Based Aircraft Landing Systems Journal Article
In: Journal of Aircraft, vol. 47, no. 4, pp. 1141-1151, 2010.
@article{Datta-Barua2010b,
title = {Ionospheric Threat Parameterization for Local Area Global-Positioning-System-Based Aircraft Landing Systems},
author = {Seebany Datta-Barua and Jiyun Lee and Sam Pullen and Ming Luo and Alexandru Ene and Di Qiu and Godwin Zhang and Per Enge},
doi = {10.2514/1.46719},
year = {2010},
date = {2010-07-01},
journal = {Journal of Aircraft},
volume = {47},
number = {4},
pages = {1141-1151},
abstract = {Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area augmentation system are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite system user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1 frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite system satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area augmentation system are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite system user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1 frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite system satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station.
2009
Lee, Jiyun, Pullen, Sam, Enge, Per
Sigma Overbounding Using a Position Domain Method for the Local Area Augmentation of GPS Journal Article
In: IEEE Transactions on Aerospace and Electronic Systems, vol. 45, no. 4, pp. 1262-1274, 2009.
@article{Lee2009b,
title = {Sigma Overbounding Using a Position Domain Method for the Local Area Augmentation of GPS},
author = {Jiyun Lee and Sam Pullen and Per Enge},
doi = {10.1109/TAES.2009.5310297},
year = {2009},
date = {2009-10-01},
journal = {IEEE Transactions on Aerospace and Electronic Systems},
volume = {45},
number = {4},
pages = {1262-1274},
abstract = {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 how a position domain method (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudo-range correction errors. Used in combination with the current range domain method (RDM), a 30% reduction in the inflation factor is achieved with the same safety standard. LAAS prototype testing verifies the utility of the PDM to enhance Category II/III user availability.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 how a position domain method (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudo-range correction errors. Used in combination with the current range domain method (RDM), a 30% reduction in the inflation factor is achieved with the same safety standard. LAAS prototype testing verifies the utility of the PDM to enhance Category II/III user availability.
2007
Lee, Jiyun, Pullen, Sam, Datta-Barua, Seebany, Enge, Per
Assessment of Ionosphere Spatial Decorrelation for Global Positioning System-Based Aircraft Landing Systems Journal Article
In: Journal of Aircraft, vol. 44, no. 5, pp. 1662-1669, 2007.
@article{Lee2007b,
title = {Assessment of Ionosphere Spatial Decorrelation for Global Positioning System-Based Aircraft Landing Systems},
author = {Jiyun Lee and Sam Pullen and Seebany Datta-Barua and Per Enge},
doi = {10.2514/1.28199},
year = {2007},
date = {2007-09-01},
journal = {Journal of Aircraft},
volume = {44},
number = {5},
pages = {1662-1669},
abstract = {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 the differential error due to the ionosphere spatial decorrelation. Both station-pair and time-step methods are used to assess the standard deviation of vertical (or zenith) ionospheric gradients (vig). The station-pair method compares the simultaneous zenith delays from two different reference stations to a single satellite and observes the difference in delay across the known ionosphere pierce point separation. Because these ionosphere pierce point separations limit the observability of the station-pair method, the time-step method is also used to better understand ionospheric gradients at short distance scales (10–40 km). The time-step method compares the ionospheric delay of a single line of sight at one epoch with the delay for the same line of sight at another epoch a short time (a few to tens of minutes) later. This method has the advantage of removing interfrequency bias calibration errors on different satellites and receivers while possibly introducing an estimation error due to temporal ionospheric gradients. The results of this study demonstrate that typical values of vig are on the order of 1–3 mm=km for nonstormy ionospheric conditions. As a result, vig of 4 mm=km is conservative enough to bound ionosphere spatial decorrelation for nominal days and still leave enough margin for more active days and for non-Gaussian tail behavior.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 the differential error due to the ionosphere spatial decorrelation. Both station-pair and time-step methods are used to assess the standard deviation of vertical (or zenith) ionospheric gradients (vig). The station-pair method compares the simultaneous zenith delays from two different reference stations to a single satellite and observes the difference in delay across the known ionosphere pierce point separation. Because these ionosphere pierce point separations limit the observability of the station-pair method, the time-step method is also used to better understand ionospheric gradients at short distance scales (10–40 km). The time-step method compares the ionospheric delay of a single line of sight at one epoch with the delay for the same line of sight at another epoch a short time (a few to tens of minutes) later. This method has the advantage of removing interfrequency bias calibration errors on different satellites and receivers while possibly introducing an estimation error due to temporal ionospheric gradients. The results of this study demonstrate that typical values of vig are on the order of 1–3 mm=km for nonstormy ionospheric conditions. As a result, vig of 4 mm=km is conservative enough to bound ionosphere spatial decorrelation for nominal days and still leave enough margin for more active days and for non-Gaussian tail behavior.
2006
Lee, Jiyun, Pullen, Sam, Enge, Per
Sigma-Mean Monitoring for the Local Area Augmentation of GPS Journal Article
In: IEEE Transactions on Aerospace and Electronic Systems, vol. 42, no. 2, pp. 625-635, 2006.
@article{Lee2006c,
title = {Sigma-Mean Monitoring for the Local Area Augmentation of GPS},
author = {Jiyun Lee and Sam Pullen and Per Enge},
doi = {10.1109/TAES.2006.1642577},
year = {2006},
date = {2006-06-19},
journal = {IEEE Transactions on Aerospace and Electronic Systems},
volume = {42},
number = {2},
pages = {625-635},
abstract = {The local area augmentation system (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. To quantitatively appraise navigation integrity, an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors, /spl sigma//sub pr/spl I.bar/gnd/, broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity risk. For sigma monitoring, the estimation method more rapidly detects small violations of /spl sigma//sub pr/spl I.bar/gnd/ but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring, the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The local area augmentation system (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. To quantitatively appraise navigation integrity, an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors, /spl sigma//sub pr/spl I.bar/gnd/, broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity risk. For sigma monitoring, the estimation method more rapidly detects small violations of /spl sigma//sub pr/spl I.bar/gnd/ but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring, the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.
Lee, Jiyun, Pullen, Sam, Enge, Per, Pervan, Boris, Gratton, Livio
Monitoring GPS Satellite Orbit Errors for Aircraft Landing Systems Journal Article
In: Journal of Aircraft, vol. 43, no. 3, pp. 799-808, 2006.
@article{Lee2006c,
title = {Monitoring GPS Satellite Orbit Errors for Aircraft Landing Systems},
author = {Jiyun Lee and Sam Pullen and Per Enge and Boris Pervan and Livio Gratton},
doi = {10.2514/1.17339},
year = {2006},
date = {2006-05-01},
journal = {Journal of Aircraft},
volume = {43},
number = {3},
pages = {799-808},
abstract = {Ground-based augmentations of the global positioning system (GPS) demand the greatest safety and reliability to support aircraft precision approach and landing navigation. One troublesome failure mode for these systems is the possibility of large orbit errors; discrepancies between the locations of GPS satellites in space and the locations derived by the ephemeris data that they broadcast. To counter this possibility, several ephemeris monitor algorithms detecting orbit errors are described. The method is based on a comparison between satellite positions given by the current satellite ephemeris [today’s ephemeris (TE)] and the ephemeris broadcast by the same satellite on its preceding pass [yesterday’s ephemeris (YE)]. Variants of this YE–TE test are shown to provide protection against ephemeris errors and also to support minimum detectable errors as low as 1145 m, which will minimize the resulting impact on ground-based augmentation system user availability. In addition, to initialize these monitors when no earlier validated ephemerides are available, means of using raw measurements are proposed. The results show that the YE–TE and the measurement-based methods together are adequate to meet navigation integrity and availability requirements for category 1 precision approaches.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ground-based augmentations of the global positioning system (GPS) demand the greatest safety and reliability to support aircraft precision approach and landing navigation. One troublesome failure mode for these systems is the possibility of large orbit errors; discrepancies between the locations of GPS satellites in space and the locations derived by the ephemeris data that they broadcast. To counter this possibility, several ephemeris monitor algorithms detecting orbit errors are described. The method is based on a comparison between satellite positions given by the current satellite ephemeris [today’s ephemeris (TE)] and the ephemeris broadcast by the same satellite on its preceding pass [yesterday’s ephemeris (YE)]. Variants of this YE–TE test are shown to provide protection against ephemeris errors and also to support minimum detectable errors as low as 1145 m, which will minimize the resulting impact on ground-based augmentation system user availability. In addition, to initialize these monitors when no earlier validated ephemerides are available, means of using raw measurements are proposed. The results show that the YE–TE and the measurement-based methods together are adequate to meet navigation integrity and availability requirements for category 1 precision approaches.