Due to the ever growing threat of Global Positioning System (GPS) spoofing, it has become necessary for the aviation sector to develop an effective means of detection. This paper focuses on two complementary spoofing detection techniques that are available on commercial GPS receivers and thus require no additional hardware to operate. The primary methodology for detection is using this combination of: Radio Power Monitoring (RPM) metrics, levering both Automatic Gain Control (AGC) and C/N0 measurements, along with multiple correlations for signal distortion to provide a best practices spoofing detection algorithm which is able to distinguish between interference and spoofing. The paper first assess nominal statistics for both metrics compiled from over 250 hours of nominal data collected from multiple Wide Area Augmentation System (WAAS) stations. This data is compared to previous collections to validate the thresholds and false alarms rates and establish a complete testing methodology. These test and thresholds are then assessed with the Texas Spoofing Test Battery (TEXBAT) series of GPS spoofing data sets to confirm detection capabilities. Finally, these test and thresholds are applied to assess the GPS signal of six extended flights over the United States to assess the performance on an aircraft.
Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate. A pump-probe spectroscopic imaging setup records pulse after pulse, and with a nanosecond time resolution, the polarized transmission spectra of the plasmonic metasurface, submitted to 50,000 ultrashort laser pulses at 75 kHz. The measurements reveal different regimes, occurring in different ranges of accumulated pulse numbers, where successive self-organized embedded periodic nanostructures with very different periods are observed by post-mortem electron microscopy characterizations. Analyses are carried out; thanks to laser-induced temperature rise simulations and calculations of the mode effective indices that can be guided in the structure. The overall study provides a detailed insight into successive mechanisms leading to shape transformation and self-organization in the system, their respective predominance as a function of the laser-induced temperature relative to the melting temperature of metallic nanoparticles and their kinetics. The article also demonstrates the dependence of the self-organized period on the guided-mode effective index, which approaches a resonance due to system transformation. Such anisotropic plasmonic metasurfaces have a great potential for security printing or data storage, and better understanding their formation opens the way to smart optimization of their properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.