Mobile crowdsensing (MCS) has gained significant attention in recent years and has become an appealing paradigm for urban sensing. For data collection, MCS systems rely on contribution from mobile devices of a large number of participants or a crowd. Smartphones, tablets, and wearable devices are deployed widely and already equipped with a rich set of sensors, making them an excellent source of information. Mobility and intelligence of humans guarantee higher coverage and better context awareness if compared to traditional sensor networks. At the same time, individuals may be reluctant to share data for privacy concerns. For this reason, MCS frameworks are specifically designed to include incentive mechanisms and address privacy concerns. Despite the growing interest in the research community, MCS solutions need a deeper investigation and categorization on many aspects that span from sensing and communication to system management and data storage. In this paper, we take the research on MCS a step further by presenting a survey on existing works in the domain and propose a detailed taxonomy to shed light on the current landscape and classify applications, methodologies, and architectures. Our objective is not only to analyze and consolidate past research but also to outline potential future research directions and synergies with other research areas.

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A Survey on Mobile Crowdsensing Systems: Challenges, Solutions, and Opportunities

Abstract. This paper presents a method to derive the ionospheric total electron content (TEC) and to estimate the biases of GPS satellites and dual frequency receivers using the GPS Earth Observation Network (GEONET) in Japan. Based on the consideration that the TEC is uniform in a small area, the method divides the ionosphere over Japan into 32 meshes. The size of each mesh is 2° by 2° in latitude and longitude, respectively. By assuming that the TEC is identical at any point within a given mesh and the biases do not vary within a day, the method arranges unknown TECs and biases with dual GPS data from about 209 receivers in a day unit into a set of equations. Then the TECs and the biases of satellites and receivers were determined by using the least-squares fitting technique. The performance of the method is examined by applying it to geomagnetically quiet days in various seasons, and then comparing the GPS-derived TEC with ionospheric critical frequencies (foF2). It is found that the biases of GPS satellites and most receivers are very stable. The diurnal and seasonal variation in TEC and foF2 shows a high degree of conformity. The method using a highly dense receiver network like GEONET is not always applicable in other areas. Thus, the paper also proposes a simpler and faster method to estimate a single receiver’s bias by using the satellite biases determined from GEONET. The accuracy of the simple method is examined by comparing the receiver biases determined by the two methods. Larger deviation from GEONET derived bias tends to be found in the receivers at lower ( Key words. Ionosphere (mid-latitude ionosphere; instruments and techniques) – Radio science (radio-wave propagation)

Ionosphere and thermosphere: Derivation of TEC and estimation of instrumental biases from GEONET in Japan

[1] The turbulent flows and tangled magnetic fields of the Earth's plasma sheet are explored theoretically and by means of ISEE-2 plasma and magnetic-field measurements. The goal is to obtain a basic understanding of (1) the dynamics, (2) the driving, and (3) the dissipation of the turbulence. Dynamically, the turbulence of the plasma sheet appears to be a turbulence of eddies, rather than a turbulence of Alfven waves or other MHD modes. In this respect, it is similar to the two-dimensional turbulence of the solar wind. Previously published statistical arguments that the correlation length (= integral scale = eddy size) of the turbulence fluctuations in the plasma sheet is leddy ∼ 1.6 RE are confirmed by analyzing plasma sheet magnetic-field measurements during two special “sweeping” intervals that follow the passage of interplanetary shocks. For dissipation of the turbulence, two mechanisms appear to be important. The first is a cascade of energy in the turbulence to small spatial scales, where internal dissipation at non-MHD spatial scales should occur. The second mechanism is electrical coupling of the turbulent flows to the resistive ionosphere, which introduces a “quasi-viscosity” to the plasma sheet. This quasi-viscosity is complicated owing (1) to a time delay associated with Alfven-transit-time coupling (introducing a viscoelasticity to the turbulence), (2) to a scalesize dependence of the coupling (introducing a hypoviscosity), and (3) to a dependence of the coupling on the sign of the flow shear (introducing a sign-vorticity effect). For the coupling of the plasma sheet turbulence to the ionosphere, retarded-time Reynolds numbers R* are derived to describe the importance of the resulting dissipation (quasi-viscosity) and a Deborah number D is derived to describe the importance of the time lag (elasticity). The difference of the plasma sheet turbulence from homogeneous turbulence is discussed; this dissimilarity is owed to (a) dissipation at all wave numbers in the plasma sheet, (b) the presence of boundaries, and (c) the limited range of spatial scales that will allow scale-invariant dynamics. A better description of the plasma sheet turbulence would be “turbulence in a box” or a turbulent wake.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009625

MHD turbulence in the Earth's plasma sheet: Dynamics, dissipation, and driving

The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

A new technique for mapping of total electron content using GPS network in Japan

Pilot observations were conducted at Arecibo, Puerto Rico, using an all-sky, image-intensified CCD camera system in conjunction with radar, ionosonde, and Global Positioning System (GPS) diagnostic systems during the periods January 19–28, 1993, and February 21 to August 22, 1995. These represent the first use of campaign mode operations of an imager at Arecibo for extended periods of F region observations. The January 1993 period (the so-called “10-day run”) yielded a rich data set of gravity wave signatures, perhaps the first case of direct imaging of thermospheric wave train properties in the F region. The 6-month 1995 campaign revealed two additional optical signatures of F region dynamics. A brightness wave in 6300 A passing rapidly through the field of view (FOV) has been linked to meridional winds driven by the midnight temperature maximum (MTM) pressure bulge. On May 3, 1995, during a period of geomagnetic activity, a 6300-A airglow depletion pattern entered the Arecibo FOV. Such effects represent the optical signatures of equatorial spread F instabilities that rise above the equator to heights near 2500 km, thereby affecting Arecibo's L = 1.4 flux tube.

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Investigations of thermospheric-ionospheric dynamics with 6300-Å images from the Arecibo Observatory

The convergence of magnetospheric energy flux in the polar atmosphere

[1] A technique is presented for inverting incoherent scatter radar (ISR) measurements of the auroral ionosphere to determine the incident electron energy spectrum. A linear model is constructed relating electron differential number flux to the volume production rate of ions, the latter derived from measured electron density profiles using a continuity equation. The forward model is inverted using the maximum entropy method (MEM). This implementation of ISR inversion was found to be remarkably robust to the principal sources of model and measurement uncertainty. The procedure was applied to high-resolution measurements (1.2 s × 1 km) by the Sondrestrom ISR recorded during an auroral surge. Analysis of bulk plasma properties in the recovered spectra suggested that the relationship between the characteristic energy and the net number flux was highly nonlinear during the onset of the auroral surge, an observation that can now be evaluated statistically. This perspective on the temporal behavior of the auroral acceleration region cannot be accessed through spaceborne measurements; ISR inversion thus constitutes a critical tool for addressing time-dependent coupling of the magnetosphere and ionosphere.

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Determination of primary electron spectra from incoherent scatter radar measurements of the auroral E region

[1] A detailed study of the effects of auroral current systems on thermal ionospheric plasma transport and loss is conducted using a new ionospheric model. The mathematical formulation of the model is a variation on the 5-moment approximation which describes the temporal evolution of density, drift, and temperature for five different ion species in two spatial dimensions. The fluid system is closed through a 2-D electrostatic treatment of the auroral currents. This model is used to examine the interplay between ion heating, perpendicular transport, molecular ion generation, and type-1 ion upflows in a self-consistent way for the first time. Simulations confirm that the depletion of E-region plasma due to current closure occurs on extremely fast time scales (5–30 s), and that it is dependent on current system scale size. Near the F-region peak, the loss is mostly due to enhanced recombination from the conversion of the plasma to molecular ions. The F-region loss process is fairly slow (120–300 s) by comparison to lower altitude processes and is highly electric field dependent. On similar time scales, transient ion upflows from frictional heating move plasma from the near topside ionosphere (∼500 km) to higher regions, leaving depletions and enhancing plasma densities at very high altitudes. Results indicate the existence of large molecular ion upflows near the F-region peak and may shed some light on ionospheric source regions for outflowing molecular ions. Neutral atmospheric winds and densities are also shown to play an important role in modulating molecular ion densities, frictional heating, and currents.

/pdf/ionospheric-plasma-transport-and-loss-in-auroral-downward-flyafad3e4.pdf

Ionospheric plasma transport and loss in auroral downward current regions

[1] An analysis of multiscale observations of a substorm auroral breakup are presented which clarify the role of wave dispersion in the formation of elemental (<100 m) auroral structure. At coarse resolution (all-sky white light camera, 1 frame/s), observations fit the established substorm morphology—namely, arc brightening, formation of spatial distortions, and breakup into multiple “rayed” structures. At fine-scale resolution (electron multiplying charge-coupled device [EMCCD] camera, 9-degree field of view, prompt emission filter, 30 frames/s), an entirely different type of coherence is observed. The “arc,” as identified at lower resolution, is observed to be a dynamic structure composed of bifurcating elemental arcs that propagate outward from the center of an “arc packet.” This dynamic process is well captured in time-brightness histories (keograms) along a cut bisecting the structure. The observations are interpreted with respect to theoretical predictions for inertial Alfven wave dispersion. Specifically, the arc packets are interpreted as the B⊥ projection of the parallel electric field within the Alfven resonant cone. Prebreakup observations are found to be qualitatively consistent with this model. However, some difficulties are encountered for the more active postbreakup period. The article includes a discussion of perspective considerations in interpreting small-scale auroral features; in particular, it is shown that the “rayed” appearance of discrete breakup aurora is, in fact, a consequence of sharply kinked sheets viewed obliquely.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JA013122

Wave dispersion and the discrete aurora: New constraints derived from high-speed imagery

Space weather refers to the conditions and evolution of Earth's near space environment including electron density variations in the ionosphere. This environment is influenced by both the Sun and terrestrial processes, and has an impact on communications, navigation, and terrestrial power systems. The recent discovery of clear signatures in the ionosphere related to tsunamis and earthquakes suggests that the ionosphere itself may serve as a valuable and versatile sensor, registering many types of Earth- and space-based phenomena. To realize this potential, ionospheric electron density must be monitored through a dense wide-area sensor mesh that is expensive to realize with traditional deployments and observation techniques. Crowdsourcing can help pursue this novel direction by providing new capabilities, including an increase in the number of sensors as well as expanding data transport capabilities through participating devices that act as relays. This article describes the Mahali project, which is currently at the beginning of exploring these promising techniques. Mahali uses GPS signals that penetrate the ionosphere for science rather than positioning. A large number of ground-based sensors will be able to feed data through mobile devices into a cloud-based processing environment, enabling a tomographic analysis of the global ionosphere at unprecedented resolution and coverage. This novel approach brings the exploitation of the ionosphere as a global earth system sensor technologically and economically within reach.

Joshua Semeter

Papers

The convergence of magnetospheric energy flux in the polar atmosphere

Determination of primary electron spectra from incoherent scatter radar measurements of the auroral E region

Ionospheric plasma transport and loss in auroral downward current regions

Wave dispersion and the discrete aurora: New constraints derived from high-speed imagery

Mobile crowd sensing in space weather monitoring: the mahali project