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- Hobiger, Thomas, 1978, et al.
(författare)
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Atmospheric Signal Propagation
- 2017
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Ingår i: Springer Handbooks. - Cham : Springer International Publishing. - 2522-8692 .- 2522-8706. ; , s. 165-193
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Global navigation satellite system (GNSS ) satellites emit signals that propagate as electromagnetic waves through space to the receivers which are located on or near the Earth’s surface or on other satellites. Thereby, electromagnetic waves travel through the ionosphere and the neutral atmosphere (troposphere) which causes signals to be delayed, damped, and refracted as the refractivity index of the propagation media is not equal to one. In this chapter, the nature and effects of GNSS signal propagation in both the troposphere and the ionosphere, aref examined. After a brief review of the fundamentals of electromagnetic waves their propagation in refractive media, the effects of the neutral atmosphere are discussed. In addition, empirical correction models as well as the state-of-the-art atmosphere delay estimation approaches are presented. Effects related to signal propagation through the ionosphere are dealt in a dedicated section by describing the error contribution of the first up to third-order terms in the refractive index and ray path bending. After discussing diffraction and scattering phenomena due to ionospheric irregularities, mitigation techniques for different types of applications are presented.
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| 2. |
- Schrijver, Carolus J., et al.
(författare)
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Understanding space weather to shield society : A global road map for 2015-2025 commissioned by COSPAR and ILWS
- 2015
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 55:12, s. 2745-2807
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Tidskriftsartikel (refereegranskat)abstract
- There is a growing appreciation that the environmental conditions that we call space weather impact the technological infrastructure that powers the coupled economies around the world. With that comes the need to better shield society against space weather by improving forecasts, environmental specifications, and infrastructure design. We recognize that much progress has been made and continues to be made with a powerful suite of research observatories on the ground and in space, forming the basis of a Sun Earth system observatory. But the domain of space weather is vast extending from deep within the Sun to far outside the planetary orbits and the physics complex including couplings between various types of physical processes that link scales and domains from the microscopic to large parts of the solar system. Consequently, advanced understanding of space weather requires a coordinated international approach to effectively provide awareness of the processes within the Sun Earth system through observation-driven models. This roadmap prioritizes the scientific focus areas and research infrastructure that are needed to significantly advance our understanding of space weather of all intensities and of its implications for society. Advancement of the existing system observatory through the addition of small to moderate state-of-the-art capabilities designed to fill observational gaps will enable significant advances. Such a strategy requires urgent action: key instrumentation needs to be sustained, and action needs to be taken before core capabilities are lost in the aging ensemble. We recommend advances through priority focus (1) on observation-based modeling throughout the Sun Earth system, (2) on forecasts more than 12 h ahead of the magnetic structure of incoming coronal mass ejections, (3) on understanding the geospace response to variable solar-wind stresses that lead to intense geomagnetically-induced currents and ionospheric and radiation storms, and (4) on developing a comprehensive specification of space climate, including the characterization of extreme space storms to guide resilient and robust engineering of technological infrastructures. The roadmap clusters its implementation recommendations by formulating three action pathways, and outlines needed instrumentation and research programs and infrastructure for each of these. An executive summary provides an overview of all recommendations.
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