1、 Recommendation ITU-R P.531-13 (09/2016) Ionospheric propagation data and prediction methods required for the design of satellite services and systems P Series Radiowave propagation ii Rec. ITU-R P.531-13 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, effici
2、ent and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are
3、performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Fo
4、rms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also
5、be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobil
6、e, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum manag
7、ement SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2016 ITU 2016 All rights reserved. No part
8、 of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.531-13 1 RECOMMENDATION ITU-R P.531-13 Ionospheric propagation data and prediction methods required for the design of satellite services and systems (Question ITU-R 218/3) (1978-1990-1992
9、-1994-1997-1999-2001-2003-2005-2007-2009-2012-2013-2016) Scope Recommendation ITU-R P.531 describes a method for evaluating of the ionospheric propagation effects on Earth-space paths at frequencies from 0.1 to 12 GHz. The following effects may take place on an Earth-space path when the signal is pa
10、ssing through the ionosphere: rotation of the polarization (Faraday rotation) due to the interaction of the electromagnetic wave with the ionized medium in the Earths magnetic field along the path; group delay and phase advance of the signal due to the total electron content (TEC) accumulated along
11、the path; rapid variation of amplitude and phase (scintillations) of the signal due to small-scale irregular structures in the ionosphere; a change in the apparent direction of arrival due to refraction; Doppler effects due to non-linear polarization rotations and time delays. The data and methods d
12、escribed in this Recommendation are applicable for planning satellite systems, in respective ranges of validity indicated in Annex 1. Keywords: Trans-ionospheric propagation, scintillation, group delay The ITU Radiocommunication Assembly, considering a) that the ionosphere causes significant propaga
13、tion effects at frequencies up to at least 12 GHz; b) that effects may be particularly significant for non-geostationary-satellite orbit services below 3 GHz; c) that experimental data have been presented and/or modelling methods have been developed that allow the prediction of the ionospheric propa
14、gation parameters needed in planning satellite systems; d) that ionospheric effects may influence the design and performance of radio systems involving spacecraft; e) that these data and methods have been found to be applicable, within the natural variability of propagation phenomena, for applicatio
15、ns in satellite system planning, recommends 1 that the data prepared and methods developed as set out in Annex 1 should be adopted for planning satellite systems, in the respective ranges of validity indicated in Annex 1. 2 Rec. ITU-R P.531-13 Annex 1 1 Introduction This annex deals with the ionosph
16、eric propagation effects on Earth-space paths. From a system design viewpoint, the impact of ionospheric effects can be summarized as follows: a) the total electron content (TEC) accumulated along a mobile-satellite service (MSS) transmission path penetrating the ionosphere causes rotation of the po
17、larization (Faraday rotation) of the MSS carrier, time delay of the signal, and a change in the apparent direction of arrival due to refraction; b) localized random ionospheric patches, commonly referred to as ionospheric irregularities, further cause excess and random rotations and time delays, whi
18、ch can only be described in stochastic terms; c) because the rotations and time delays relating to electron density are non-linearly frequency dependent, both a) and b) further result in dispersion or group velocity distortion of the MSS carriers; d) furthermore, localized ionospheric irregularities
19、 also act like convergent and divergent lens which focus and defocus the radio waves. Such effects are commonly referred to as the scintillations which affect amplitude, phase and angle-of-arrival of the MSS signal. Due to the complex nature of ionospheric physics, system parameters affected by iono
20、spheric effects as noted above cannot always be succinctly summarized in simple analytic formulae. Relevant data edited in terms of tables and/or graphs, supplemented with further descriptive or qualifying statements, are for all practical purposes the best way to present the effects. In considering
21、 propagation effects in the design of MSS at frequencies below 3 GHz, one has to recognize that: e) the normally known space-Earth propagation effects caused by hydrometeors are not significant relative to effects of f) and h); f) the near surface multipath effects, in the presence of natural or man
22、-made obstacles and/or at low elevation angles, are always critical; g) the near surface multipath effects vary from locality to locality, and therefore they do not dominate the overall design of the MSS system when global scale propagation factors are to be dealt with; h) ionospheric effects are th
23、e most significant propagation effects to be considered in the MSS system design in global scale considerations. 2 Background Caused by solar radiation, the Earths ionosphere consists of several regions of ionization. For all practical communications purposes, regions of the ionosphere, D, E, F and
24、top-side ionization have been identified as contributing to the TEC between satellite and ground terminals. In each region, the ionized medium is neither homogeneous in space nor stationary in time. Generally speaking, the background ionization has relatively regular diurnal, seasonal and 11-year so
25、lar cycle variations, and is dependent strongly on geographical locations and geomagnetic activity. In addition to the background ionization, there are always highly dynamic, small-scale non-stationary structures known as irregularities. Both the background ionization and irregularities degrade radi
26、owaves. Furthermore, the refractive index is frequency dependent, i.e. the medium is dispersive. Rec. ITU-R P.531-13 3 3 Prime degradations due to background ionizations A number of effects, such as refraction, dispersion and group delay, are in magnitude directly proportional to the TEC; Faraday ro
27、tation is also approximately proportional to TEC, with the contributions from different parts of the ray path weighted by the longitudinal component of magnetic field. A knowledge of the TEC thus enables many important ionospheric effects to be estimated quantitatively. 3.1 TEC Denoted as NT, the TE
28、C can be evaluated by: s eT ssnN d)(1) where: s : propagation path (m) ne : electron concentration (el/m3). Even when the precise propagation path is known, the evaluation of NT is difficult because ne has diurnal, seasonal and solar cycle variations. For modelling purposes, the TEC value is usually
29、 quoted for a zenith path having a cross-section of 1 m2. The TEC of this vertical column can vary between 1016 and 1018 el/m2 with the peak occurring during the sunlit portion of the day. For estimating the TEC, either a procedure based on the International Reference Ionosphere (IRI-2012) or a more
30、 flexible procedure, also suitable for slant TEC evaluation and based on NeQuick2 v.P531-12, are available. Both procedures are provided below. 3.1.1 IRI-2012-based method The standard monthly median ionosphere is the COSPAR-URSI IRI-2012. Under conditions of low to moderate solar activity numerical
31、 techniques may be used to derive values for any location, time and chosen set of heights up to 2 000 km. Under conditions of high solar activity, problems may arise with values of electron content derived from IRI-2012. For many purposes it is sufficient to estimate electron content by multiplicati
32、on of the peak electron density with an equivalent slab thickness value of 300 km. 3.1.2 NeQuick2-based method The electron density distribution given by the model is represented by a continuous function that is also continuous in all spatial first derivatives. It consists of two parts, the bottom-s
33、ide part (below the peak of the F2-layer) and the top-side part (above the F2-layer peak). The peak height of the F2-layer is calculated from M(3000)F2 and the ratio foF2/foE (see Recommendation ITU-R P.1239). The bottom-side is described by semi-Epstein layers for representing E, F1 and F2. The top
34、-side F layer is again a semi-Epstein layer with a height dependent thickness parameter. The NeQuick2 v.P531-12 model gives the electron density and TEC along arbitrary ground-to-satellite or satellite-to-satellite paths. The computer program and associated data files are integral digital products t
35、o this Recommendation and are available in the file R-REC-P.531-12-201309-I!ZIP-E. 4 Rec. ITU-R P.531-13 3.2 Faraday rotation When propagating through the ionosphere, a linearly polarized wave will suffer a gradual rotation of its plane of polarization due to the presence of the geomagnetic field an
36、d the anisotropy of the plasma medium. The magnitude of Faraday rotation, , will depend on the frequency of the radiowave, the magnetic field strength, and the electron density of the plasma as: 2141036.2 f NB Tav(2) where: : angle of rotation (rad) Bav : average Earth magnetic field (Wb m2 or Tesla
37、s) f : frequency (GHz) NT : TEC (electrons m2). Typical values of are shown in Fig. 1. FIGURE 1 Faraday rotation as a function of TEC and frequency The Faraday rotation is thus inversely proportional to the square of frequency and directly proportional to the integrated product of the electron densi
38、ty and the component of the Earths magnetic field along the propagation path. Its median value at a given frequency exhibits a very regular diurnal, seasonal, and solar cyclical behaviour that can be predicted. This regular component of the Faraday rotation can therefore be compensated for by a manu
39、al adjustment of the polarization tilt angle at the earth-station antennas. However, large deviations from this regular behaviour can occur for small percentages of the time as a result of geomagnetic storms and, to a lesser extent, large-scale travelling ionospheric disturbances. These deviations c
40、annot be predicted in advance. Intense and fast fluctuations of the Faraday rotation angles of VHF signals have been associated with strong and fast amplitude scintillations respectively, at locations situated near the crests of the equatorial anomaly. 102110103104101102101610171018F r e que nc y (
41、G H z )Faradayrotation(rad)10 e l / m19 21 0.1 0.2 0.5 2 5 100.3 0.4Rec. ITU-R P.531-13 5 The cross-polarization discrimination for aligned antennas, XPD (dB), is related to the Faraday rotation angle, , by: XPD 20 log (tan ) (3) 3.3 Group delay The presence of charged particles in the ionosphere sl
42、ows down the propagation of radio signals along the path. The time delay in excess of the propagation time in free space, commonly denoted as t, is called the group delay. It is an important factor to be considered for MSS systems. Likewise, the phase is advanced by the same amount. This quantity ca
43、n be computed as follows: t 1.345 NT / f 2 107 (4) where: t : delay time (s) with reference to propagation in a vacuum f : frequency of propagation (Hz) NT : determined along the slant propagation path. Figure 2 is a plot of time delay, t, versus frequency, f, for several values of electron content
44、along the ray path. For a band of frequencies around 1 600 MHz the signal group delay varies from approximately 0.5 to 500 ns, for TEC from 1016 to 1019 el/m2. Figure 3 shows the yearly percentage of daytime hours that the time delay will exceed 20 ns at a period of relatively high solar activity. 3
45、.4 Dispersion When trans-ionospheric signals occupy a significant bandwidth the propagation delay (being a function of frequency) introduces dispersion. The differential delay across the bandwidth is proportional to the integrated electron density along the ray path. For a fixed bandwidth the relati
46、ve dispersion is inversely proportional to frequency cubed. Thus, systems involving wideband transmissions must take this effect into account at VHF and possibly UHF. For example, as shown in Fig. 4 for an integrated electron content of 5 1017 el/m2, a signal with a pulse length of 1 s will sustain
47、a differential delay of 0.02 s at 200 MHz while at 600 MHz the delay would be only 0.00074 s (see Fig. 4). 3.5 TEC rate of change With an orbiting satellite the observed rate of change of TEC is due in part to the change of direction of the ray path and in part to a change in the ionosphere itself.
48、For a satellite at a height of 22 000 km traversing the auroral zone, a maximum rate of change of 0.7 1016 el/m2/s has been observed. For navigation purposes, such a rate of change corresponds to an apparent velocity of 0.11 m/s. 6 Rec. ITU-R P.531-13 FIGURE 2 Ionospheric time delay versus frequency
49、 for various values of electron content Ionospherictimedelay(s)F r e que nc y ( M H z )100 200 1 000500 2 000 3 0001042525252525251019e l / m2101610171018103102101110102Rec. ITU-R P.531-13 7 FIGURE 3 Contours of percentage of yearly average daytime hours when time delay at vertical incidence at 1.6 GHz exceeds 20 ns (sunspot number = 140) FIGURE 4 Difference in the time delay between the lower and upper frequencies of the spectrum of a pulse of width, , transmitted through the ionosphere, one way traversal LatitudeL ong i t ude 9
