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In this paper, we present an algorithmic framework for signal‐geometry‐based approaches of GNSS spoofing detection. We formulate a simple vs. simple hypothesis test independent of nuisance parameters that results in significantly reduced missed detection probability compared to prior approaches. It is highly tractable such that it can be computed online by the receiver. We employ a hypothesis iteration framework that finds spoofed subsets of satellites efficiently and accounts for the presence of weak multipath, for a provable decision behavior in safety‐of‐life applications. We support the theoretical derivations by showing results on previously published simulated and on‐air data sets. We validate the measurement model and show robustness to multipath with flight data from a Dual Polarization Antenna (DPA) mounted on a C12 aircraft. Finally, we show the algorithm's benefit on data recorded during a government‐sponsored live spoofing event. [ABSTRACT FROM AUTHOR]

Integral to any authentication system is the design of its public key infrastructure (PKI), allowing the system to distribute, maintain, and revoke cryptographic keys while dividing and allocating the responsibility of security between different entities. This paper develops a PKI for two SBAS candidate authentication schemes: one each for an L5 I‐channel and Q‐channel implementation. A simulator, introduced as MCOS, is developed to enable large scale Monte Carlo tests of these PKI designs. This work concludes that once a receiver has been deployed with a set of preinstalled encrypted public keys, a strictly over‐the‐air method of delivering PKI information is feasible for SBAS data authentication in nominal conditions. This work also provides a strong candidate PKI that is designed to be standardized internationally for current and future SBAS service providers. [ABSTRACT FROM AUTHOR]

Cryptography in the form of digital signatures can be part of the solution to the threat of spoofing and is going to be implemented on Galileo and other Global Navigation Satellite Systems. Digital signatures incorporated into the data stream authenticate the integrity of the data as well as the origin of the message. Implementing a digital signature on a satellite‐based augmentation system for use in aviation will require the signature to be short and the signing procedure to be cryptographically relevant for the next 30 or more years. With the advent of quantum computing, many state‐of‐the‐art authentication schemes are no longer viable, so an authentication scheme implemented in satellite‐based augmentation system will need to be quantum secure. This paper introduces the cryptographic primitives (foundational problems) necessary to understand the vulnerabilities in modern‐day cryptography due to quantum computing and investigates the use of TESLA (Timed Efficient Stream Loss‐tolerant Algorithm) and EC‐Schnorr (Elliptic Curve‐Schnorr) algorithms in broadcast systems. [ABSTRACT FROM AUTHOR]

Effective natural resource planning depends on understanding the prevalence of runoff generating processes. Within a specific area of interest, this demands reproducible, straightforward information that can complement available local data and can orient and guide stakeholders with diverse training and backgrounds. To address this demand within the contiguous United States (CONUS), we characterized and mapped the predominance of two primary runoff generating processes: infiltration‐excess and saturation‐excess runoff (IE vs. SE, respectively). Specifically, we constructed a gap‐filled grid of surficial saturated hydraulic conductivity using the Soil Survey Geographic and State Soil Geographic soils databases. We then compared surficial saturated hydraulic conductivity values with 1‐hr rainfall‐frequency estimates across a range of return intervals derived from CONUS‐scale random forest models. This assessment of the prevalence of IE versus SE runoff also incorporated a simple uncertainty analysis, as well as a case study of how the approach could be used to evaluate future alterations in runoff processes resulting from climate change. We found a low likelihood of IE runoff on undisturbed soils over much of CONUS for 1‐hr storms with return intervals <5 years. Conversely, IE runoff is most likely in the Central United States (i.e., Texas, Louisiana, Kansas, Missouri, Iowa, Nebraska, and Western South Dakota), and the relative predominance of runoff types is highly sensitive to the accuracy of the estimated soil properties. Leveraging publicly available data sets and reproducible workflows, our approach offers greater understanding of predominant runoff generating processes over a continental extent and expands the technical resources available to environmental planners, regulators, and modellers. [ABSTRACT FROM AUTHOR]

The Wide Area Augmentation System (WAAS) achieved Initial Operating Capability (IOC) in July 2003. At IOC, WAAS had 25 reference stations in the Conterminous United States, Hawaii, Alaska, and San Juan, Puerto Rico, two master stations, and four uplink stations supporting two narrowband L1 only Geostationary Earth Orbit (GEO) satellites. Today, WAAS has 38 reference stations including four in Canada and five in Mexico, three master stations, and six uplink stations supporting three wide band L1/L5 GEO satellites. In addition to the architectural expansion, the Federal Aviation Administration (FAA) continued to evolve and maintain the algorithms, hardware, and software. With WAAS now turning 15 years of age, this paper takes stock of these modifications and details the improved service and integrity that has occurred since 2003. [ABSTRACT FROM AUTHOR]

Abstract: There has been resurgent interest in building low Earth orbiting (LEO) constellations of satellites on a new scale. Their aim is Internet for the world with plans for potentially thousands of satellites. Here, we explore how these LEO constellations can be utilized for navigation. Closer to Earth, LEO offers stronger signals, strengthening us against jamming and aiding in indoor and urban environments. Proximity is also its weakness, where satellites have a small Earth footprint requiring many to provide global coverage. We show that the strength of the Broadband LEO constellations is their numbers, where they offer threefold improvement in satellite geometry compared to navigation core‐constellations today. This allows for relaxation of the signal‐in‐space user range error, while still matching the position accuracy of GPS. Coupled with the more benign radiation environment in LEO compared to GPS in medium Earth orbit, this enables a navigation payload designed using commercial‐off‐the‐shelf components. © 2018 Institute of Navigation [ABSTRACT FROM AUTHOR]

Abstract: This paper examines how to evaluate observed instantaneous signal‐in‐space errors and determine suitable upper bounds on their likely distribution. We compare this performance against the commitments and broadcast values from the satellites to determine whether the provided values are sufficient or not. An important aspect is to characterize the errors in light of known or predictable characteristics. Oftentimes, errors are grouped together to create a single averaged distribution. However, there may be times and conditions where performance is notably worse. We need to separate out such conditions and evaluate the distributions individually so as not to form overly optimistic estimates of the error bounds. Further, we must ensure that these parameters will continue to bound future fault‐free behavior. We will describe the conservative steps taken in the estimation process and the validation effort, both with the real data and versus the stated commitments from the constellation service providers. Copyright © 2018 Institute of Navigation [ABSTRACT FROM AUTHOR]

We present a fault exclusion algorithm and a formula for the position error bounds after an exclusion event for Advanced Receiver Autonomous Integrity Monitoring. This algorithm has both a low computational load and an analytical proof of integrity. To mitigate the loss of performance associated with false exclusion, the method both exploits the ambiguity as to which measurement must be excluded and a pre-allocation of the integrity budget to the exclusion outcomes. The algorithm is evaluated for a GPS-Galileo Advanced RAIM scenario. We show that with this algorithm, the addition of the exclusion option does not impact the protection levels compared to detection only and that when the faults are large enough, the effect on the user is equivalent to the effect of an outage. Copyright © 2017 Institute of Navigation [ABSTRACT FROM AUTHOR]

This paper describes an efficient new algorithm being developed for the Wide Area Augmentation System (WAAS) that significantly improves its ability to detect threats arising from multiple simultaneous one to two sigma errors. This new algorithm is based on the sum of the squares of the normalized errors at each reference station. It has significantly improved the ability to detect error conditions that are not obviously faulted individually, but that could be harmful to users when combined. Currently, other monitors are inflating the confidence bounds to protect against such conditions. This new User Position Monitor (UPM) is able to identify such threats, and as a consequence, excess conservatism may be removed from the system. We expect this innovation to lead to better availability while maintaining equal or better levels of integrity. Copyright © 2017 Institute of Navigation [ABSTRACT FROM AUTHOR]

One of the most commonly used detection statistics in autonomous integrity monitoring is the solution separation statistic. In this paper, we show that the solution separation statistic is closely linked to the optimal detection statistics. More precisely, we show that in the case of one threat, even multi-dimensional, the optimal detection statistic is the solution separation, and that in the case of many one-dimensional threats, the optimal statistics can be expressed as a function of the solution separations corresponding to each threat. This is achieved by casting the search of the optimal detection region as a mini-max problem and by using the Neyman-Pearson lemma to limit the search of the detection regions to a class of regions parameterized by a bias. These results allow us to establish a lower bound on the minimum achievable integrity risk. Copyright © 2017 Institute of Navigation [ABSTRACT FROM AUTHOR]

Growing activity in the Arctic calls for high integrity navigation in this region. This can be achieved using Global Navigation Satellite Systems (GNSS) in conjunction with Satellite Based Augmentation Systems (SBAS) or Advanced Receiver Autonomous Integrity Monitoring (ARAIM). Single frequency GPS-only SBAS is in service in some regions today and is reliant on ground and space infrastructure. ARAIM will be more autonomous and will rely on the multitude of signals and core constellations coming in the future. Here, we examine both SBAS and ARAIM in the context of aviation and maritime requirements in the Arctic. Results demonstrate that the introduction of multi-frequency and multi-constellation to these systems enables navigation safety in the Arctic. SBAS brings aircraft precision approach as well as precise maritime operations such as mapping. ARAIM also supports precision approach in addition to autonomous ice navigation at sea but falls short of precision maritime requirements. Copyright © 2016 Institute of Navigation [ABSTRACT FROM AUTHOR]

Pyrogenic carbon (PyC) is important because of its role in the global organic C (OC) cycle and in modifying soil properties. However, our understanding of PyC movement from terrestrial to fluvial ecosystems is not robust. This study examined (i)whether erosion or subsurface transport wasmore important for PyC export from headwaters, (ii) whether PyC was exported preferentially to total OC (TOC), and (iii) whether themovement of PyC from terrestrial to aquatic ecosystems provides an explanation for the coupling of PyC and non-PyC observed in rivers at a global scale. In the Guineo-Congolian highland forest region of western Kenya, duplicate catchments with sizes of 1-12 ha were equipped with stream gauges in primary forest and adjacent mixed agricultural landscapes that were cleared by fire 10, 16, or 62 years before. Stream water samples were taken weekly throughout 1 year and compared with runoff to assess PyC movement. Additional stream samples were taken fromall major tributaries of theWhite Nile watershed of Lake Victoria. PyC was not found to be preferentially eroded relative to TOC or non-PyC, as topsoil (0-0.15m) PyC concentrations (6.3 ± 0.3% of TOC; means and standard errors) were greater than runoff sediment (1.9 ± 0.4%) and dissolved PyC concentrations (2.0 ± 0.4%, n= 252). In addition, PyC proportions in eroded sediment were lower than and uncorrelated (r²=0.04; P= 0.14) with topsoil PyC. An enrichment of PyC was found with depth in the soil, from 6.3 ± 0.3% of TOC in the topsoil (0-0.15 m) to 12.3 ± 0.3% of TOC at 1-2m. Base flow PyC proportions of TOC correlated well with subsoil PyC (r²=0.57; P<0.05) but not with topsoil PyC (r2=0.18; P>0.05). Similar PyC proportions were found in the studied headwater streams (2.7 ± 0.2%), their downstream inflow into Lake Victoria (3.7%), the other ninemajor rivers into Lake Victoria (4.9 ± 0.8%), and its outflow into the White Nile (1.1%). A strong positive correlation between dissolved PyC and non-PyC (r² = 0.91; P<0.0001) in the headwater streams reflect relationships previously seen for a range of globally important rivers, and contrasts with a negative relationship for suspended sediments (r2 =-0.5; P<0.0001). The estimated PyC export from the Lake Victoria watershed of 11 Gg yr-1 may therefore originate to a large extent from subsoil pathways in dissolved form that appeared to be an important source of PyC in aquatic environments and may explain the coupling of PyC and non-PyC at a global scale. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a method to improve the integrity error bound in Advanced RAIM by optimizing the position solution and the integrity allocation simultaneously. Since the reduction in the error bound is achieved by degrading the position accuracy under nominal conditions, the method takes into account the accuracy constraint in the optimization. Advanced RAIM may have to consider a larger number of satellites and increased probabilities of fault, so this method is designed to accept a wide variety of threat models (in particular multiple faults). The search of the optimal coefficients is cast as a convex optimization problem with constraints. The solution is obtained iteratively, and the convexity of the problem guarantees a very fast convergence. The algorithm is evaluated by comparing its performance with algorithms where the position solution is not optimized, and showing how it could help achieve worldwide coverage of vertical guidance (LPV-200). Copyright © 2013 Institute of Navigation [ABSTRACT FROM AUTHOR]

ABSTRACT The GNSS environment is experiencing two major changes: the introduction of a new civil signal in the L5 band and the launch of new GNSS constellations. These improvements could enable worldwide vertical guidance using Advanced Receiver Autonomous Integrity Monitoring (ARAIM). Before ARAIM can be implemented, it will be necessary to develop a common understanding across service providers of the navigation requirements, the threat model, the airborne algorithm, and the role of ground monitoring. We outline a concept for the provision of integrity based on ARAIM. First, an interpretation of vertical guidance (LPV-200) requirements is proposed. Then, we describe a comprehensive threat model for GNSS which includes both nominal performance and faulted behavior. We will show how the threats could be mitigated through the use of ground monitoring and the Integrity Support Message in addition to the ARAIM airborne algorithm. Finally, examples of constellation configurations providing worldwide coverage of LPV-200 are presented. Copyright © 2013 Institute of Navigation. [ABSTRACT FROM AUTHOR]

ABSTRACT GPS has launched its first L5 capable satellites and plans to achieve L5 Full Operational Capability (FOC) in the 2019 time frame. L5 is of great interest to the Wide Area Augmentation System (WAAS) and the aviation community, as it will allow aircraft to measure and remove the ionospheric delay affecting each ranging observation. Currently, this error source is the most significant cause of unavailability for WAAS users. Its elimination will result in greater performance and a larger service area under WAAS. However, in order to take advantage of L5, both the aircraft and WAAS will need to be updated. We have previously recommended changes to the airborne protection level calculations to exploit these new signals. In this paper we describe changes that should then be made to WAAS to support the new protection level equations and provide dual-frequency service. Copyright © 2012 Institute of Navigation [ABSTRACT FROM AUTHOR]

The article presents a study on the development of a method to predict baseflow buffering chemistry which is based on the hydrogeomorphic properties of watersheds in Neversink River Basin in New York State. The study employs regression analysis which shows that low acid-neutralizing capacity (ANC) watersheds have higher potential for quickflow runoff. The study reveals that the hydrogeomorphic properties can help determine the sensitivity of watershed to acid deposition.