Ground-level Signal Research Articles

Performance of ground-level signal detection when using a phone while walking

Ground-level traffic lights or safety signs have been introduced recently as a prevention measure for smartphone-related pedestrian accidents. However, quantitative evaluation of smartphone users' detection performance during distracted walking has been scarce. A laboratory experiment was conducted to evaluate the performance of detecting ground-level visual cues during the concurrent use of a smartphone while walking. Thirty-eight young smartphone users performed ground-level visual cue detection trials, 1) while walking upright on a treadmill without using a smartphone; 2) when conducting one-handed browsing while walking; and, 3) when conducting two-handed texting while walking. Visual cues were presented on the ground at 24 locations by a ceiling-mounted projector, and participants were asked to respond verbally when they perceived the appearance of each cue. Study results show that the concurrent use of a smartphone decreased the detection rate significantly (p < 0.05) from 93.5 % to 76.3∼74.1 %, and increased the reaction time from 0.90 s to 1.04∼1.15 s. Among the 24 cue locations, cues that were presented closer to participants were detected significantly (p < 0.05) more often and faster than cues that were shown at further locations. The results of this laboratory-based study imply that the ground-level signals might not be detected well by smartphone users, specifically when they were conducting more demanding tasks such as texting while walking. However, the laboratory conditions were confined to a specific usage environment; therefore, future research should be focused on the situation awareness of smartphone users under various usage scenarios and more realistic environments.

Subsurface mass transport affects the radioxenon signatures that are used to identify clandestine nuclear tests

AbstractThe ratios of noble gas radioisotopes can provide critical information with which to verify that a belowground nuclear test has taken place. The relative abundance of anthropogenic isotopes is typically assumed to rely solely on their fission yield and decay rate. The xenon signature of a nuclear test is then bounded by the signal from directly produced fission xenon, and by the signal that would come from the addition of xenon from iodine precursors. Here we show that this signal range is too narrowly defined. Transport simulations were done to span the range of geological conditions within the Nevada Test Site. The simulations assume a 1 kt test and the barometric history following the nuclear test at Pahute Mesa in March 1992. Predicted xenon ratios fall outside of the typically assumed range 20% of the time and situations can arise where the ground level signal comes entirely from the decay of iodine precursors.

Ground level signal strength of electromagnetic waves generated by pulsed electron beams in space

A theoretical study has been made of the signal strengths at ground level of waves generated by pulsed electron beams in space. Such beams might be generated by pulsed electron guns aboard either a satellite or a rocket. The radiated energy is first calculated by an improved version of a theory based on coherent spontaneous emission. This theory evaluates the electric and magnetic field strengths and power fluxes in the far field by applying asymptotic expansion techniques. With this information at hand, the power flowing out within a cone whose apex is located at the gun position is calculated. Finally, the intersection of the rays in this cone with the Earth's surface is determined by using Snell's law considerations. Ground signal levels are calculated for typical ionospheric conditions as a function of pulsing frequency for fixed beam voltage and for voltage adjusted for resonance between the waves and the particles. For short beams, the ground level signal strengths are relatively insensitive to the wave particle resonance condition, but for longer beams the associated peaking of the signal level begins to be observed. Finally, these results are compared against ambient noise levels to determine under which circumstances these ground signals can be detected.

Ionospheric heating with oblique high‐frequency waves

This paper presents calculations of ionospheric electron temperature and density perturbations and ground‐level signal changes produced by intense oblique high‐frequency (HF) radio waves. Our analysis takes into account focusing at caustics, the consequent Joule heating of the surrounding plasma, heat conduction, diffusion, and recombination processes, these being the effects of a powerful oblique “modifying” wave. It neglects whatever plasma instabilities might occur. We then seek effects on a secondary “test” wave that is propagated along the same path as the first. Our calculations predict ground‐level field strength reductions of several decibels in the test wave for modifying waves having effective radiated power (ERP) in the 85‐ to 90‐dBW range. These field strength changes are similar in sign, magnitude, and location to ones measured in Soviet experiments. The location of the signal change is sensitive to the frequency and the model ionosphere assumed; so future experiments should employ the widest possible range of frequencies and propagation conditions. An ERP of 90 dBW seems to be a sort of threshold that, if exceeded, might result in substantial rather than small signal changes. Our conclusions are based solely on Joule heating and subsequent refraction of waves passing through caustic regions.

Geomagnetic fluctuations due to impulse sources with applications to high-altitude nuclear bursts

The response of the ionosphere-exosphere system to a bomb-like hydromagnetic source and the resultant time-dependent ground-level magnetic fluctuations are examined theoretically in this paper, with emphasis placed upon gaining an understanding of the time behavior of the ground-level signal. The methods of calculation are also applicable to certain magnetic fluctuations of natural origin. An analytic treatment is used, whereby the problem is reduced essentially to finding the poles and residues of previously derived hydromagnetic transmission coefficients. Conditions corresponding to high magnetic latitudes are used, but some conclusions corresponding to more general conditions are drawn. Bomb-induced ground-level magnetic fluctuations are interpreted in terms of a broadband excitation of ionospheric and exospheric resonant oscillations. Even for broadband sources, which excite all of the many resonances, the signal rapidly becomes dominated by the lowest characteristic frequencies. Thus, for a wide range of source functions, the frequency content of the transmitted signal would be determined largely by the resonant properties of the propagation medium. Two examples of this are the magnetic fluctuations measured after the Argus and Starfish high-altitude nuclear tests. For hypothetical high-latitude bursts detonated in or above the lower ionosphere, the ground-level signal is predicted to be nearly left-hand circularly polarized in the daytime and to exhibit nearly the polarization of the source at night. For many situations of practical interest, the enhancement of the lower ionospheric ionization density by bomb X rays is a very important consideration.