A Technique for Determining the Carrier Phase Differences between Independent GPS Receivers during Scintillation

A method for recovering the carrier phase differences between pairs of independent GPS receivers has been developed and demonstrated in truth-model simulations. This effort is in support of a project that intends to image the disturbed ionosphere with diffraction tomography techniques using GPS measurements from large arrays of receivers. Carrier phase differential GPS techniques, common in surveying and relative navigation, are employed to determine the phase relationships between the receivers in the imaging array. Strategies for estimating the absolute carrier phase disturbances at each receiver are discussed. Simulation results demonstrate that the system can rapidly detect the onset of scintillation, identify one non-scintillating reference signal, and recover the carrier phase differences accurate to 0.1 cycles.Aerospace Engineering and Engineering Mechanic

GPS Carrier Tracking Loop Performance in the presence of Ionospheric Scintillations

The performance of several GPS carrier tracking loops is evaluated using wideband GPS data recorded during strong ionospheric scintillations. The aim of this study is to determine the loop structures and parameters that enable good phase tracking during the power fades and phase dynamics induced by scintillations. Constant-bandwidth and variable-bandwidth loops are studied using theoretical models, simulation, and tests with actual GPS signals. Constant-bandwidth loops with loop bandwidths near 15 Hz are shown to lose phase lock during scintillations. Use of the decision-directed discriminator reduces the carrier lock threshold by ∼1 dB relative to the arctangent and conventional Costas discriminators. A proposed variablebandwidth loop based on a Kalman filter reduces the carrier lock threshold by more than 7 dB compared to a 15-Hz constant-bandwidth loop. The Kalman filter-based strategy employs a soft-decision discriminator, explicitly models the effects of receiver clock noise, and optimally adapts the loop bandwidth to the carrier-to-noise ratio. In extensive simulation and in tests using actual wideband GPS data, the Kalman filter PLL demonstrates improved cycle slip immunity relative to constant bandwidth PLLs.Aerospace Engineering and Engineering Mechanic

Individual and institutional determinants of the male female wage gap among U.S. economics faculty

This paper provides new evidence on the male female wage gap in academia. Using unique data from the economics discipline, we estimate a human-capital based model to explore the nature of wage differentials among male and female economics professors. Results indicate the salary gap varies across systematically across individual and institutional characteristics.discrimination, wages, academia

Near-optimal protocols in complex nonequilibrium transformations

The development of sophisticated experimental means to control nanoscale systems has motivated efforts to design driving protocols which minimize the energy dissipated to the environment. Computational models are a crucial tool in this practical challenge. We describe a general method for sampling an ensemble of finite-time, nonequilibrium protocols biased towards a low average dissipation. We show that this scheme can be carried out very efficiently in several limiting cases. As an application, we sample the ensemble of low-dissipation protocols that invert the magnetization of a 2D Ising model and explore how the diversity of the protocols varies in response to constraints on the average dissipation. In this example, we find that there is a large set of protocols with average dissipation close to the optimal value, which we argue is a general phenomenon.Comment: 6 pages and 3 figures plus 4 pages and 5 figures of supplemental materia

Analysis of Ionospheric Scintillations using Wideband GPS L1 C/A Signal Data

A non-real-time GPS receiver has been developed and tested for use in scintillation analysis. The receiver consists of a digital storage receiver and non-real-time software acquisition and tracking algorithms. The goal of this work is to shed light on the behavior of strongly scintillating signals: signals which cause conventional GPS receivers to lose carrier lock. The receiver collects wideband GPS L1 digital data sampled at 5.7 MHz using an RF front-end and stores it on disk for post-processing. It processes the data off-line to determine carrier signal amplitude and phase variations during scintillations. The main processing algorithms are traditional code delay and carrier frequency acquisition algorithms and special signal processing algorithms that effectively function as a delay-locked loop and phase-locked loop. The tracking algorithms use non-causal smoothing techniques in order to optimally reconstruct the phase and amplitude variations of a scintillating signal. These techniques are robust against the deep power fades and strong phase fluctuations characteristic of scintillating signals. To test the receiver, scintillation data were collected in Cauchoeira Paulista, Brazil, from December 4 to 6, 2003. The data set spans several hours and includes times when one or more satellite signals are scintillating. The smoothing algorithm has been used to determine the carrier amplitude and phase time histories of the scintillating signals along with the distortion of the pseudorandom noise (PRN) code’s autocorrelation function. These quantities provide a characterization of scintillation that can be used to study the physics of scintillations or to provide off-line test cases to evaluate a tracking algorithm’s ability to maintain signal lock during scintillations.Aerospace Engineering and Engineering Mechanic

GNSS Signal Authentication via Power and Distortion Monitoring

We propose a simple low-cost technique that enables civil Global Positioning System (GPS) receivers and other civil global navigation satellite system (GNSS) receivers to reliably detect carry-off spoofing and jamming. The technique, which we call the Power-Distortion detector, classifies received signals as interference-free, multipath-afflicted, spoofed, or jammed according to observations of received power and correlatio n function distortion. It does not depend on external hardware or a network connection and can be readily implemented on many receivers via a firmware update. Crucially, the detector can with high probability distinguish low-power spoofing from ordinary multipath. In testing against over 25 high-quality empirical data sets yielding over 900,000 separate detection tests, the detector correctly alarms on all malicious spoofing or jamming attack s while maintaining a <0.5% single-channel false alarm rate.Aerospace Engineering and Engineering Mechanic

Assessing the Spoofing Threat: Development of a Portable GPS Civilian Spoofer

A portable civilian GPS spoofer is implemented on a digital signal processor and used to characterize spoofing effects and develop defenses against civilian spoofing. This work is intended to equip GNSS users and receiver manufacturers with authentication methods that are effective against unsophisticated spoofing attacks. The work also serves to refine the civilian spoofing threat assessment by demonstrating the challenges involved in mounting a spoofing attack.Aerospace Engineering and Engineering Mechanic

Intensive Archaeological Survey of Portions of the Proposed Sand Hills Loop Phase I Pipeline, Reagan and Crockett Counties, Texas

On behalf of DCP Sand Hills Pipeline, LLC (DCP), SWCA Environmental Consultants (SWCA) conducted an intensive archaeological survey of portions of the proposed Sand Hills Loop Phase I Pipeline in Reagan and Crockett counties, Texas. Approximately 26 miles of the pipeline (“project”) crosses through land owned by the University of Texas (UT). The majority of the proposed alignment has been previously investigated by Turpin and Sons, Inc. in 2011. As such, only portions of the alignment that deviate outside the 2011 survey corridor were investigated, as well as portions which cross or are adjacent to (within 300 feet) sites that were identified after the 2011 survey. These areas to be surveyed total 6.4 miles within a 100-foot-wide corridor (approx. 78 acres). Archaeological investigations were conducted pursuant to the potential acquisition of a U.S. Army Corps of Engineers (USACE) Section 404 permit in accordance with 33 Code of Federal Regulations (CFR) Part 325, Appendix C (Processing Department of Army Permits: Procedures for the Protection of Historic Properties; Final Rule 1990; with current Interim Guidance Documents dated April 25, 2005 and January 31, 2007); and Section 106 of the National Historic Preservation Act (NHPA) (16 United States Code [USC] 470) and its implementing regulations 36 CFR 800. As the project area is owned by a political subdivision of the State of Texas, work was additionally conducted in compliance with the Antiquities Code of Texas (Texas Natural Resource Code, Title 9, Chapter 191) and accompanying Rules of Practice and Procedure (Texas Administrative Code, Title 13, Chapter 26) under Texas Antiquities Permit No. 8157. As a result of the current investigation, nine cultural resources were identified or revisited. These include seven previously recorded archaeological sites (41CX1096, 41CX1317, 41CX1570, 41RG76, 41RG263, 41RG324, and 41RG343) located within or immediately adjacent to the survey corridor, in addition to two newly-identified sites (41RG389 and 41RG390) and one isolated find (UT-CX-50a-1). All cultural resources identified or revisited during the course of the investigation were assessed with regard to eligibility for the National Register of Historic Places (NRHP) and designation as a State Antiquities Landmark (SAL) and recommendation for avoidance, if applicable, as follows: Two sites (41RG389 and 41RG390) and one isolated find (UT-CX-50a-1) are recommended NOT ELIGIBLE for the NRHP or for designation as a SAL. Owing to the paucity or commonality of recovered assemblages, lack of features, lack of unique character, and/or lack of contextual integrity, these resources possess negligible research value and are unlikely to contribute to the understanding of local and/or regional prehistory or history. Consequently, no further work was recommended for these resources. The investigated portions of five sites (41RG76, 41RG263, 41RG343, 41CX1096, and 41CX1317) within the proposed workspace are recommended NOT ELIGIBLE for the NRHP or for designation as a SAL. Owing to the paucity or commonality of recovered assemblages, lack of features, lack of unique character, and/or lack of contextual integrity, the investigated portions of these resources possess negligible research value and are unlikely to contribute to the understanding of local and/or regional prehistory or history. The remaining unevaluated portions of these sites will not be affected by the proposed project; therefore, no further work was recommended for these sites at this time. Two sites (41RG324 and 41CX1570) are located outside the proposed workspace and will not be impacted by the proposed project. Each of these sites are UNDETERMINED with regard to NRHP and SAL eligibility. As the proposed construction activities will have NO IMPACT on these sites, no additional work or avoidance measures are recommended at this time. In accordance with Section 106 of the NHPA 36 CFR 800.4 (b)(1) and the Antiquities Code of Texas, SWCA has made a reasonable and good faith effort to identify significant cultural resources within the project area. No properties listed or otherwise eligible for the NRHP, or for designation as a SAL were identified within the project area. Consequently, SWCA recommends no further archaeological investigation and a finding of NO HISTORIC PROPERTIES AFFECTED under 36 CFR 800.4(d)(1). Per requirements of the Antiquities Code of Texas, project documentation will be curated with the Texas Archeological Research Laboratory in Austin