In this work, we present a Global Navigation Satellite Systems (GNSS) satellite fault detection, identification, and exclusion method for an integrated GNSS/Inertial Navigation System (INS) tightly-coupled navigation architecture. Observed satellite fault profiles and magnitudes are taken as a baseline to design the monitor. Normalized innovations for each satellite are utilized to observe the respective satellite faults on each channel. A sufficient test statistic for each satellite channel is derived using the generalized likelihood ratio test (GLRT). We develop a method for quantifying missed detection rates given fault profile and magnitude. This developed methodology is capable of providing protection levels using the INS-only coasting solution. We also describe an identification and exclusion method using consecutive windows of the monitor without the need for running parallel Kalman filters (KF). We validate the developed algorithm for the detection, identification and exclusion of faulty satellites using simulated fault scenarios.
{"title":"GNSS Satellite Fault Detection and Exclusion for Integrated GNSS/INS Systems","authors":"Birendra Kujur, Samer Khanafseh, Boris Pervan","doi":"10.33012/2023.19448","DOIUrl":"https://doi.org/10.33012/2023.19448","url":null,"abstract":"In this work, we present a Global Navigation Satellite Systems (GNSS) satellite fault detection, identification, and exclusion method for an integrated GNSS/Inertial Navigation System (INS) tightly-coupled navigation architecture. Observed satellite fault profiles and magnitudes are taken as a baseline to design the monitor. Normalized innovations for each satellite are utilized to observe the respective satellite faults on each channel. A sufficient test statistic for each satellite channel is derived using the generalized likelihood ratio test (GLRT). We develop a method for quantifying missed detection rates given fault profile and magnitude. This developed methodology is capable of providing protection levels using the INS-only coasting solution. We also describe an identification and exclusion method using consecutive windows of the monitor without the need for running parallel Kalman filters (KF). We validate the developed algorithm for the detection, identification and exclusion of faulty satellites using simulated fault scenarios.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lin Zhao, Xitie Lu, Hui Li, Renlong Wang, Ziheng Gao
The precise ultra-rapid orbit is a prerequisite to providing accurate Positioning, Navigation and Timing (PNT) service. There are the orbit boundary discontinuities (OBDs) in adjacent ultra-rapid orbits. The OBD will decrease the accuracy of the positioning service at the orbit boundary. The traditional time-weighted calibration algorithm based on the fixed orbital arc length depends on the broadcast latter orbit, which cannot meet the requirement of the real-time application. By assigning the weights of overlapping orbits according to time, an adaptive calibration algorithm is proposed to correct the latter orbit. The evaluation results have shown that the OBD calibration accuracy and the orbit accuracy loss are improved 12.27% and 9.87%, respectively. The OBD verification results have shown that the PPP accuracy at the boundary is improved 5%. It is confirmed that the OBD can be improved effectively based on the adaptive calibration algorithm, which can be applied for the real-time PPP.
{"title":"A Calibration Algorithm of Ultra-rapid Orbit Boundary Discontinuity based on Adaptive Orbital Arc Length","authors":"Lin Zhao, Xitie Lu, Hui Li, Renlong Wang, Ziheng Gao","doi":"10.33012/2023.19185","DOIUrl":"https://doi.org/10.33012/2023.19185","url":null,"abstract":"The precise ultra-rapid orbit is a prerequisite to providing accurate Positioning, Navigation and Timing (PNT) service. There are the orbit boundary discontinuities (OBDs) in adjacent ultra-rapid orbits. The OBD will decrease the accuracy of the positioning service at the orbit boundary. The traditional time-weighted calibration algorithm based on the fixed orbital arc length depends on the broadcast latter orbit, which cannot meet the requirement of the real-time application. By assigning the weights of overlapping orbits according to time, an adaptive calibration algorithm is proposed to correct the latter orbit. The evaluation results have shown that the OBD calibration accuracy and the orbit accuracy loss are improved 12.27% and 9.87%, respectively. The OBD verification results have shown that the PPP accuracy at the boundary is improved 5%. It is confirmed that the OBD can be improved effectively based on the adaptive calibration algorithm, which can be applied for the real-time PPP.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Evan Anzalone, Lemuel Carpenter, Cheryl Gramling, Laurie Mann, Thomas Moody
The early Artemis missions represent the return of humanity to the surface of the Moon and provide opportunities for meeting early science and exploration goals. Position, Navigation, and Timing (PNT) capabilities are a fundamental element and inform operational design, flight rules, and the ability to meet these. This paper provides an overview of the needs, potential implementations, challenges, and concepts of operations in the initial human surface missions, Artemis III and IV. These early excursions are a crucial learning opportunity to gain more experience in the actual operational environment for Artemis V and beyond where exploration objectives and complexity increases. As part of the study, the team defined a threshold performance navigation requirement (including position and orientation) to meet crew safe return and assessed a breadth of navigation approaches that could be deployed to augment the crew’s baseline navigation capability. Data was collected in terms of size, mass, power, operational constraints, environment constraints, interface, and performance to define the technical metrics. Given these, the trade team conducted polling among the various Artemis Campaign elements to capture preference, integration challenges, and operational impacts. These were used to develop weightings and inform a ranked order of solutions across each of the early missions. The results of the study recommended augmenting the initial orientation capability with additional navigation sensors to provide coarse position and heading information to the crew to enable a safe contingency walk-back when out of video range. The team identified opportunities for embedding this hardware in future scenarios to provide an integrated solution. With the deployment of the LunaNet’s Lunar Augmented Navigation System, the crew will be able to maintain accurate real-time navigation knowledge with minimal physical impacts. Discussion of future testing and continued analysis is included in this paper. These forward plans and long-term architecture systems will enable a powerful navigation approach for orbiting and surface users, enabling a high level of scientific return and crew safety.
{"title":"Early Artemis Surface Navigation: Challenges, Approaches, and Opportunities","authors":"Evan Anzalone, Lemuel Carpenter, Cheryl Gramling, Laurie Mann, Thomas Moody","doi":"10.33012/2023.19274","DOIUrl":"https://doi.org/10.33012/2023.19274","url":null,"abstract":"The early Artemis missions represent the return of humanity to the surface of the Moon and provide opportunities for meeting early science and exploration goals. Position, Navigation, and Timing (PNT) capabilities are a fundamental element and inform operational design, flight rules, and the ability to meet these. This paper provides an overview of the needs, potential implementations, challenges, and concepts of operations in the initial human surface missions, Artemis III and IV. These early excursions are a crucial learning opportunity to gain more experience in the actual operational environment for Artemis V and beyond where exploration objectives and complexity increases. As part of the study, the team defined a threshold performance navigation requirement (including position and orientation) to meet crew safe return and assessed a breadth of navigation approaches that could be deployed to augment the crew’s baseline navigation capability. Data was collected in terms of size, mass, power, operational constraints, environment constraints, interface, and performance to define the technical metrics. Given these, the trade team conducted polling among the various Artemis Campaign elements to capture preference, integration challenges, and operational impacts. These were used to develop weightings and inform a ranked order of solutions across each of the early missions. The results of the study recommended augmenting the initial orientation capability with additional navigation sensors to provide coarse position and heading information to the crew to enable a safe contingency walk-back when out of video range. The team identified opportunities for embedding this hardware in future scenarios to provide an integrated solution. With the deployment of the LunaNet’s Lunar Augmented Navigation System, the crew will be able to maintain accurate real-time navigation knowledge with minimal physical impacts. Discussion of future testing and continued analysis is included in this paper. These forward plans and long-term architecture systems will enable a powerful navigation approach for orbiting and surface users, enabling a high level of scientific return and crew safety.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"97 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Open Service Navigation Message Authentication (OSNMA) serves as a critical security mechanism for the Galileo global navigation satellite system. At the core of OSNMA is a Timed Efficient Stream Loss-tolerant Authentication (TESLA) scheme, which generates a tag for each navigation message using a secret key and later discloses the key to receivers for authenticating the message-tag pair. Despite its great effectiveness against spoofing attacks, OSNMA’s ability to resist replay attacks is questionable since the replayed signals containing authentic messages and tags may bypass the authentication under certain circumstances. This paper, for the first time, reveals two serious vulnerabilities of OSNMA: time synchronization (TS) and non-continuous message authentication (NCMA). TS is a mandatory requirement that specifies that the difference between a receiver’s local reference time and the Galileo System Time (GST) extracted from Galileo signals does not exceed a given threshold. Exploiting this vulnerability, we propose a pre-startup replay (PreRep) attack, where Galileo signals are continuously recorded and replayed to a victim receiver before it starts up such that the TS requirement is satisfied and the receiver is locked to the replayed signals. NCMA means that OSNMA temporarily suspends the authentication process probably due to the reception of a broken message, tag or key, and restores the authentication after receiving a later-disclosed valid message-tag-key pair. Based on this vulnerability, we propose a post-startup replay (PosRep) attack, which conducts the replay attack after the victim receiver starts up such that the replayed signals break the currently receiving message-tag-key pair, deliberately suspending the authentication process, while subsequently-replayed signals can pass the authentication successfully as the message-tag-key pairs inside are valid. Finally, we conducted extensive experiments based on real-world OSNMA-integrated receivers and two software-defined radio (SDR) devices to demonstrate the feasibility of the proposed attacks.
{"title":"Novel Replay Attacks Against Galileo Open Service Navigation Message Authentication","authors":"Haiyang Wang, Yuanyu Zhang, Yulong Shen, Jinxiao Zhu, Yin Chen, Xiaohong Jiang","doi":"10.33012/2023.19397","DOIUrl":"https://doi.org/10.33012/2023.19397","url":null,"abstract":"Open Service Navigation Message Authentication (OSNMA) serves as a critical security mechanism for the Galileo global navigation satellite system. At the core of OSNMA is a Timed Efficient Stream Loss-tolerant Authentication (TESLA) scheme, which generates a tag for each navigation message using a secret key and later discloses the key to receivers for authenticating the message-tag pair. Despite its great effectiveness against spoofing attacks, OSNMA’s ability to resist replay attacks is questionable since the replayed signals containing authentic messages and tags may bypass the authentication under certain circumstances. This paper, for the first time, reveals two serious vulnerabilities of OSNMA: time synchronization (TS) and non-continuous message authentication (NCMA). TS is a mandatory requirement that specifies that the difference between a receiver’s local reference time and the Galileo System Time (GST) extracted from Galileo signals does not exceed a given threshold. Exploiting this vulnerability, we propose a pre-startup replay (PreRep) attack, where Galileo signals are continuously recorded and replayed to a victim receiver before it starts up such that the TS requirement is satisfied and the receiver is locked to the replayed signals. NCMA means that OSNMA temporarily suspends the authentication process probably due to the reception of a broken message, tag or key, and restores the authentication after receiving a later-disclosed valid message-tag-key pair. Based on this vulnerability, we propose a post-startup replay (PosRep) attack, which conducts the replay attack after the victim receiver starts up such that the replayed signals break the currently receiving message-tag-key pair, deliberately suspending the authentication process, while subsequently-replayed signals can pass the authentication successfully as the message-tag-key pairs inside are valid. Finally, we conducted extensive experiments based on real-world OSNMA-integrated receivers and two software-defined radio (SDR) devices to demonstrate the feasibility of the proposed attacks.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Precise Point Positioning (PPP) is a technique that provides high global accuracy without the need for nearby reference stations. The approach, at minimum, requires GNSS satellite orbit and clock errors generated from globally distributed reference stations to achieve high accuracy. End users can then utilize either an ionosphere-free linear combination to eliminate the first order of ionosphere delays or an undifferenced and uncombined model to estimate ionosphere delays. Hemisphere Atlas is an innovative global L-band service from Hemisphere GNSS, which has global coverage. The Galileo High Accuracy service (HAS) is a free service provided by the European Union with Interface Control Document (ICD) published in May 2022. The HAS will have two service levels: Service Level 1 with global coverage orbits, clocks, and code biases, and Service Level 2 with regional coverage of atmospheric corrections. Initial assessments of Service Level 1 have already shown that it meets expectations around the world. Atlas H10 has a 95% accuracy of 8cm, and Galileo HAS achieves a 95% accuracy of 20cm. Therefore, Galileo HAS can be an excellent backup to Atlas in case of service outage or severe interference on the L-Band frequency of Atlas. In this article, Atlas and HAS global performance will first be introduced. Next, we will present their actual performance metrics from five different locations spanning five continents, and subsequently provide insights into the switching logic. Lastly, a patent-pending dual redundant service using Hemisphere Atlas and Galileo HAS will be introduced, with higher priority given to Atlas.
{"title":"Enhancing Global PPP Service Reliability with Hemisphere Atlas® and Galileo HAS: A Dual Redundant Approach","authors":"Jianping Chen, Viet Duong, Alim Kanji","doi":"10.33012/2023.19441","DOIUrl":"https://doi.org/10.33012/2023.19441","url":null,"abstract":"Precise Point Positioning (PPP) is a technique that provides high global accuracy without the need for nearby reference stations. The approach, at minimum, requires GNSS satellite orbit and clock errors generated from globally distributed reference stations to achieve high accuracy. End users can then utilize either an ionosphere-free linear combination to eliminate the first order of ionosphere delays or an undifferenced and uncombined model to estimate ionosphere delays. Hemisphere Atlas is an innovative global L-band service from Hemisphere GNSS, which has global coverage. The Galileo High Accuracy service (HAS) is a free service provided by the European Union with Interface Control Document (ICD) published in May 2022. The HAS will have two service levels: Service Level 1 with global coverage orbits, clocks, and code biases, and Service Level 2 with regional coverage of atmospheric corrections. Initial assessments of Service Level 1 have already shown that it meets expectations around the world. Atlas H10 has a 95% accuracy of 8cm, and Galileo HAS achieves a 95% accuracy of 20cm. Therefore, Galileo HAS can be an excellent backup to Atlas in case of service outage or severe interference on the L-Band frequency of Atlas. In this article, Atlas and HAS global performance will first be introduced. Next, we will present their actual performance metrics from five different locations spanning five continents, and subsequently provide insights into the switching logic. Lastly, a patent-pending dual redundant service using Hemisphere Atlas and Galileo HAS will be introduced, with higher priority given to Atlas.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper addresses the limitations of using global navigation satellite systems (GNSS) for positioning in indoor environments, which can experience signal attenuation and blockage from walls. Although there are various indoor positioning techniques available, they typically require additional hardware and cannot provide seamless navigation between indoor and outdoor environments. To overcome these limitations, this paper introduces Tuti, a GNSS-based advanced repeater designed and developed by IGASPIN GmbH. For this purpose, the desired indoor area is virtually divided into small zones, each covered by a directional antenna that transmits Tuti's GNSS signals. This leads the user's calculated position to the approximate actual coordinate in that zone. Tuti's signals are precisely synchronized with GNSS satellites, enabling seamless indoor/outdoor navigation and smooth tracking during the user's transitions between coverage zones. The test results reported in this paper demonstrate how Tuti can provide low-cost indoor positioning with accuracy comparable to outdoor positioning without requiring extra hardware or assistance from the user. Furthermore, it will be discussed that Tuti's capabilities are not limited to indoor applications, such as the transition of cars from the production line in the factory to outside parking slots but also can enhance positioning accuracy in areas with limited visibility to the sky, such as mountainous regions.
{"title":"Tuti: An Advanced GNSS-Based Repeater for Seamless Indoor/Outdoor Positioning","authors":"Amir Tabatabaei","doi":"10.33012/2023.19408","DOIUrl":"https://doi.org/10.33012/2023.19408","url":null,"abstract":"This paper addresses the limitations of using global navigation satellite systems (GNSS) for positioning in indoor environments, which can experience signal attenuation and blockage from walls. Although there are various indoor positioning techniques available, they typically require additional hardware and cannot provide seamless navigation between indoor and outdoor environments. To overcome these limitations, this paper introduces Tuti, a GNSS-based advanced repeater designed and developed by IGASPIN GmbH. For this purpose, the desired indoor area is virtually divided into small zones, each covered by a directional antenna that transmits Tuti's GNSS signals. This leads the user's calculated position to the approximate actual coordinate in that zone. Tuti's signals are precisely synchronized with GNSS satellites, enabling seamless indoor/outdoor navigation and smooth tracking during the user's transitions between coverage zones. The test results reported in this paper demonstrate how Tuti can provide low-cost indoor positioning with accuracy comparable to outdoor positioning without requiring extra hardware or assistance from the user. Furthermore, it will be discussed that Tuti's capabilities are not limited to indoor applications, such as the transition of cars from the production line in the factory to outside parking slots but also can enhance positioning accuracy in areas with limited visibility to the sky, such as mountainous regions.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Matthias Schäfer, Steve Sõeruer, Taavi Kippak, Erkki Sadrak
GPS jamming has emerged as a significant threat, with ramifications extending across various sectors, especially in the realm of air traffic surveillance. This paper delves into the synergistic application of ADS-B data as a tool for the detection of large-scale GPS jamming attacks. By tapping into this resource, we demonstrate a system that continuously and promptly detects these threats over expansive regions. Analyzing data from our European network segment over a one-year period, we offer an in-depth characterization of the detected interference. In addition, we propose a novel method for locating the source of the interference under circumstances where existing methods fail. More specifically, existing methods are inadequate when the jammed area is not fully covered or air traffic is sparse. Addressing these gaps, we introduce a novel localization method that uses the ADS-B-based observations to reconstruct the GPS jammer’s radio horizon and then uses this information to determine its location.
{"title":"Jammer on the Horizon: A Robust Method for GPS Jammer Localization Using ADS-B Data","authors":"Matthias Schäfer, Steve Sõeruer, Taavi Kippak, Erkki Sadrak","doi":"10.33012/2023.19393","DOIUrl":"https://doi.org/10.33012/2023.19393","url":null,"abstract":"GPS jamming has emerged as a significant threat, with ramifications extending across various sectors, especially in the realm of air traffic surveillance. This paper delves into the synergistic application of ADS-B data as a tool for the detection of large-scale GPS jamming attacks. By tapping into this resource, we demonstrate a system that continuously and promptly detects these threats over expansive regions. Analyzing data from our European network segment over a one-year period, we offer an in-depth characterization of the detected interference. In addition, we propose a novel method for locating the source of the interference under circumstances where existing methods fail. More specifically, existing methods are inadequate when the jammed area is not fully covered or air traffic is sparse. Addressing these gaps, we introduce a novel localization method that uses the ADS-B-based observations to reconstruct the GPS jammer’s radio horizon and then uses this information to determine its location.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ting Ni, Hang Guo, Min Yu, Jian Xiong, Qun Tian, Longfei Lv, Sai Du
As an important parameter in meteorological research, precipitable water vapor (PWV) can reflect atmospheric water vapor variations. PWV obtained through the inversion of global navigation satellite systems (GNSS) has the advantages of high accuracy, low cost, and high spatial-temporal resolution. In Hong Kong, frequent lightning activity is observed due to topographic and climatic conditions, and GNSS PWV can be used to analyze the lightning activity. GAMIT can derive accurate atmospheric information from GNSS observations. First, the zenith total delay (ZTD) of six IGS stations worldwide were calculated at different satellite elevation cutoff angles. It was found that the highest precision of ZTD was obtained at a satellite elevation cutoff angle of 10°, with an average RMSE (MAE) of 2.94mm (2.28 mm) for the six IGS stations. Second, when using GAMIT to calculate PWV, different mapping functions can yield different results. The PWV is solved by using the satellite observation data of HKSC station in Hong Kong, and it is found that the highest accuracy of PWV is obtained when using VMF1, and its RMSE (MAE) is 2.43 m (1.79 mm). Third, a study of 63 lightning events in the vicinity of HKSC and HKKT stations from May to October 2021 in the Hong Kong region reveals that the onset of lightning is usually preceded by a decreasing process of PWV. It was found that there is typically a decrease in PWV before the occurrence of lightning. Among the studied lightning events, 60.32% were associated with a decrease in PWV, while 39.68% were associated with an increase in PWV. Moreover, 73% of lightning events occurred within three hours before or after the lowest point of PWV during this decrease process. These results show that GNSS PWV has great potential for short-term proximity prediction of lightning in Hong Kong.
可降水量(PWV)是气象研究中的一个重要参数，可以反映大气水汽的变化。通过全球导航卫星系统(GNSS)反演得到的PWV具有精度高、成本低、时空分辨率高等优点。在香港，由于地形和气候条件，闪电活动频繁，GNSS PWV可用来分析闪电活动。GAMIT可以从GNSS观测中获得准确的大气信息。首先，计算了全球6个IGS站点在不同卫星高程截止角度下的天顶总时延(ZTD);结果表明，卫星高程截止角为10°时ZTD精度最高，平均均方根误差(MAE)为2.94mm (2.28 mm)。其次，在使用GAMIT计算PWV时，不同的映射函数会产生不同的结果。利用香港HKSC站的卫星观测资料对PWV进行求解，发现VMF1获得的PWV精度最高，其RMSE (MAE)为2.43 m (1.79 mm)。第三，对香港地区从2021年5月至10月在HKSC和HKKT站附近发生的63次闪电事件的研究表明，闪电的发生通常是在PWV减弱的过程之前。研究发现，在闪电发生前，PWV有一个典型的下降。在研究的闪电事件中，60.32%的闪电事件与PWV减少有关，39.68%的闪电事件与PWV增加有关。在此过程中，73%的闪电发生在PWV最低点前后3小时内。这些结果显示GNSS PWV系统在香港闪电的短期近距离预测方面有很大的潜力。
{"title":"Water Vapor Retrieved from Ground-Based GNSS and its Applications in Lightning Weather in Hong Kong","authors":"Ting Ni, Hang Guo, Min Yu, Jian Xiong, Qun Tian, Longfei Lv, Sai Du","doi":"10.33012/2023.19204","DOIUrl":"https://doi.org/10.33012/2023.19204","url":null,"abstract":"As an important parameter in meteorological research, precipitable water vapor (PWV) can reflect atmospheric water vapor variations. PWV obtained through the inversion of global navigation satellite systems (GNSS) has the advantages of high accuracy, low cost, and high spatial-temporal resolution. In Hong Kong, frequent lightning activity is observed due to topographic and climatic conditions, and GNSS PWV can be used to analyze the lightning activity. GAMIT can derive accurate atmospheric information from GNSS observations. First, the zenith total delay (ZTD) of six IGS stations worldwide were calculated at different satellite elevation cutoff angles. It was found that the highest precision of ZTD was obtained at a satellite elevation cutoff angle of 10°, with an average RMSE (MAE) of 2.94mm (2.28 mm) for the six IGS stations. Second, when using GAMIT to calculate PWV, different mapping functions can yield different results. The PWV is solved by using the satellite observation data of HKSC station in Hong Kong, and it is found that the highest accuracy of PWV is obtained when using VMF1, and its RMSE (MAE) is 2.43 m (1.79 mm). Third, a study of 63 lightning events in the vicinity of HKSC and HKKT stations from May to October 2021 in the Hong Kong region reveals that the onset of lightning is usually preceded by a decreasing process of PWV. It was found that there is typically a decrease in PWV before the occurrence of lightning. Among the studied lightning events, 60.32% were associated with a decrease in PWV, while 39.68% were associated with an increase in PWV. Moreover, 73% of lightning events occurred within three hours before or after the lowest point of PWV during this decrease process. These results show that GNSS PWV has great potential for short-term proximity prediction of lightning in Hong Kong.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"439 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zixi Liu, Juan Blanch, Sherman Lo, Yu-Hsuan Chen, Todd Walter
GNSS serves safety-of-life applications in aviation such as precise navigation for approach and landing operations. Interference events happen near airport can severely affect the safe operations of the airspace. Two events in 2022, one at Dallas-Fort Worth International Airport (KDFW) and another at Denver International Airport (KDEN) caused widespread disruptions resulting in multiple aircraft reporting GPS unreliable within 30-40NM of the airport. Being able to quickly detect the existence of GNSS interference events can help reduce the safety or operational risks caused by such disruptions. This paper examines the use of Automatic Dependent Surveillance—Broadcast (ADS-B) to detect GNSS radio frequency interference (RFI). ADS-B is a surveillance system which has aircraft broadcasting its position every 0.4 – 0.6 sec. The position message contains a quality indicator which describes the accuracy and integrity of GPS performance. Depending on the severity of the interference experienced, ADS-B might stop broadcasting or report low position quality. Either result can be used to identify existence of GPS interference. ADS-B is already widely in use by commercial aircraft and there are many companies and academic networks that receive and offer ADS-B data. The ubiquity and openness of ADS-B provides an available widespread source of GNSS information. This study aims to develop an algorithm which can perform rapid detection of GNSS interference events using filtered ADS-B data. The algorithm needs to be able to detect multiple concurrent events while minimizing false alerts. The ultimate goal is to design a system of algorithms that is able to monitor the entire U.S. and provide immediate and reliable information about potential GPS interference events. The algorithm was tested and validated using data collected from real interference events.
{"title":"Real Time Detection and Estimation of GNSS Interference Affected Region Using ADS-B Data and Bayesian Modeling","authors":"Zixi Liu, Juan Blanch, Sherman Lo, Yu-Hsuan Chen, Todd Walter","doi":"10.33012/2023.19466","DOIUrl":"https://doi.org/10.33012/2023.19466","url":null,"abstract":"GNSS serves safety-of-life applications in aviation such as precise navigation for approach and landing operations. Interference events happen near airport can severely affect the safe operations of the airspace. Two events in 2022, one at Dallas-Fort Worth International Airport (KDFW) and another at Denver International Airport (KDEN) caused widespread disruptions resulting in multiple aircraft reporting GPS unreliable within 30-40NM of the airport. Being able to quickly detect the existence of GNSS interference events can help reduce the safety or operational risks caused by such disruptions. This paper examines the use of Automatic Dependent Surveillance—Broadcast (ADS-B) to detect GNSS radio frequency interference (RFI). ADS-B is a surveillance system which has aircraft broadcasting its position every 0.4 – 0.6 sec. The position message contains a quality indicator which describes the accuracy and integrity of GPS performance. Depending on the severity of the interference experienced, ADS-B might stop broadcasting or report low position quality. Either result can be used to identify existence of GPS interference. ADS-B is already widely in use by commercial aircraft and there are many companies and academic networks that receive and offer ADS-B data. The ubiquity and openness of ADS-B provides an available widespread source of GNSS information. This study aims to develop an algorithm which can perform rapid detection of GNSS interference events using filtered ADS-B data. The algorithm needs to be able to detect multiple concurrent events while minimizing false alerts. The ultimate goal is to design a system of algorithms that is able to monitor the entire U.S. and provide immediate and reliable information about potential GPS interference events. The algorithm was tested and validated using data collected from real interference events.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fixing ambiguity to a correct integer value is an essential part of high-accuracy positioning using the global navigation satellite system (GNSS) real-time kinematic (RTK). A lot of research has been done on this problem in the past decades. The least-squares ambiguity decorrelation adjustment (LAMBDA) is widely applied for estimating integer ambiguity. In general, the float ambiguity variables are resolved based on the least square estimation using the double-differenced code and carrier measurements. Then the integer ambiguity is resolved by the LAMBDA method which exploits the information content of the full ambiguity variance-covariance matrix, with statistical decorrelation as the objective in constructing the ambiguity transformation. One of the well-recognized challenges of the LAMBDA method is its reliance on the covariance matrix associated with float ambiguity. Moreover, the correlation between the float parameters and the integer ambiguities is not fully explored in the two-step optimization. Instead of resolving the integer ambiguity in a two-step-based manner, can we directly resolve the float state (position of the user) and integer ambiguities simultaneously in a tighter manner? To answer this question, this paper exploits to use of the mixed-integer program (MIP) to solve the GNSS-RTK positioning problem. In particular, the classical branch and bound algorithm of MIP is applied in this research. This algorithm uses a divide-and-conquer strategy to partition the solution space into subproblems and then optimizes individually over each subproblem, in order to find the best solution globally. At each subproblem in the branch and bound algorithm, the position parameter and integer ambiguity are estimated simultaneously to minimize the objective function. In this paper, epoch-by-epoch positioning experiment shows that the positioning performance can be improved a lot based on an MIP method when compared with the conventional method. Moreover, integer ambiguity can be obtained for all epochs. For some epochs, when LAMBDA cannot fix ambiguity successfully, the MIP method can get a reasonable integer value for ambiguity to improve the position accuracy. Compared with the conventional method, the newly proposed algorithm doesn’t directly rely heavily on the quality of float ambiguity estimation and the associated covariance which is indispensable for conventional LAMBDA algorithms. We can get integer ambiguity directly along with ambiguity-fixed position results in one step via the MIP method.
{"title":"A New GNSS Ambiguity Resolution Method Through Mixed Integer Programming","authors":"Hongmin Zhang, Weisong Wen, Li-Ta Hsu","doi":"10.33012/2023.19317","DOIUrl":"https://doi.org/10.33012/2023.19317","url":null,"abstract":"Fixing ambiguity to a correct integer value is an essential part of high-accuracy positioning using the global navigation satellite system (GNSS) real-time kinematic (RTK). A lot of research has been done on this problem in the past decades. The least-squares ambiguity decorrelation adjustment (LAMBDA) is widely applied for estimating integer ambiguity. In general, the float ambiguity variables are resolved based on the least square estimation using the double-differenced code and carrier measurements. Then the integer ambiguity is resolved by the LAMBDA method which exploits the information content of the full ambiguity variance-covariance matrix, with statistical decorrelation as the objective in constructing the ambiguity transformation. One of the well-recognized challenges of the LAMBDA method is its reliance on the covariance matrix associated with float ambiguity. Moreover, the correlation between the float parameters and the integer ambiguities is not fully explored in the two-step optimization. Instead of resolving the integer ambiguity in a two-step-based manner, can we directly resolve the float state (position of the user) and integer ambiguities simultaneously in a tighter manner? To answer this question, this paper exploits to use of the mixed-integer program (MIP) to solve the GNSS-RTK positioning problem. In particular, the classical branch and bound algorithm of MIP is applied in this research. This algorithm uses a divide-and-conquer strategy to partition the solution space into subproblems and then optimizes individually over each subproblem, in order to find the best solution globally. At each subproblem in the branch and bound algorithm, the position parameter and integer ambiguity are estimated simultaneously to minimize the objective function. In this paper, epoch-by-epoch positioning experiment shows that the positioning performance can be improved a lot based on an MIP method when compared with the conventional method. Moreover, integer ambiguity can be obtained for all epochs. For some epochs, when LAMBDA cannot fix ambiguity successfully, the MIP method can get a reasonable integer value for ambiguity to improve the position accuracy. Compared with the conventional method, the newly proposed algorithm doesn’t directly rely heavily on the quality of float ambiguity estimation and the associated covariance which is indispensable for conventional LAMBDA algorithms. We can get integer ambiguity directly along with ambiguity-fixed position results in one step via the MIP method.","PeriodicalId":498211,"journal":{"name":"Proceedings of the Satellite Division's International Technical Meeting","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135483468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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