Space environment (natural and artificial) — The Earth's ionosphere model — International reference ionosphere (IRI) model and extensions to the plasmasphere

This document provides guidance to potential users for the specification of the global distribution of ionosphere densities and temperatures, as well as the total content of electrons in the height interval from 50 km to 1 500 km. It includes and explains several options for a plasmaspheric extension of the model, embracing the geographical area between latitudes of 80°S and 80°N and longitudes of 0°E to 360°E, for any time of day, any day of year, and various solar and magnetic activity conditions. A brief introduction to ionospheric and plasmaspheric physics is given in Annex A. Annex B provides an overview over physical models, because they are important for understanding and modelling the physical processes that produce the ionospheric plasma.

Environnement spatial (naturel et artificiel) — Modèle de l'ionosphère de la Terre — Modèle de l'ionosphère internationale de référence (IRI) et extensions à la plasmasphère

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INTERNATIONAL ISO
STANDARD 16457
Second edition
2022-02
Space environment (natural and
artificial) — The Earth's ionosphere
model — International reference
ionosphere (IRI) model and
extensions to the plasmasphere
Environnement spatial (naturel et artificiel) — Modèle de
l'ionosphère de la Terre — Modèle de l'ionosphère internationale de
référence (IRI) et extensions à la plasmasphère
Reference number
ISO 16457:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO 16457:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 16457:2022(E)
Contents  Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2  Normative references ..................................................................................................................................................................................... 1

3  Terms and definitions .................................................................................................................................................................................... 1

4  Abbreviated terms ............................................................................................................................................................................................. 3

5  General considerations .................................................................................................................................................................................4

6 Applicability.............................................................................................................................................................................................................. 4

7  Model description ...............................................................................................................................................................................................4

8  Model content and inputs ........................................................................................................................................................................... 5

9  Real-time IRI ............................................................................................................................................................................................................ 6

10  Plasmasphere extension of the IRI model ................................................................................................................................ 6

10.1 General ........................................................................................................................................................................................................... 6

10.2 Extrapolation of IRI profiles ....................................................................................................................................................... 6

10.3 Global core plasma model (GCPM) ........................................................................................................................................ 6

10.4 IMAGE/RPI plasmasphere model........................................................................................................................................... 6

10.5 IZMIRAN plasmasphere model ................................................................................................................................................ 6

11  Accuracy of the model ....................................................................................................................................................................................7

Annex A (informative) Brief introduction to ionosphere and plasmasphere physics ....................................8

Annex B (informative) Physical models ........................................................................................................................................................... 9

Bibliography .............................................................................................................................................................................................................................13

iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 16457:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 14, Space systems and operations.

This second edition cancels and replaces the first edition (ISO 16457:2014), which has been technically

revised.
The main changes are as follows:
— adding a description of the newly developed real-time IRI (Clause 9);

— replacing one of the plasmaspheric extension models (GPID) that is no longer available with the

option to extrapolate the standard IRI to plasmaspheric altitudes;

— providing more detail and newer references for the IMAGE/RPI and IZMIRAN plasmaspheric

extensions of IRI.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 16457:2022(E)
Introduction

The purpose of this document is to identify a set of management guidelines for dealing with space

systems engineering activities and is intended to define the minimum existing processes on the subject

seeking to reach an international agreement on the topic.

Guided by the knowledge gained from empirical data analysis, this document provides guidelines

for specifying the global distribution of electron density, electron temperature, ion temperature,

ion composition, and total electron content through the Earth’s ionosphere and plasmasphere. The

model recommended for the representation of these parameters in the ionosphere is the international

reference ionosphere (IRI).

IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the

International Union of Radio Science (URSI). These organizations formed a working group in the late

1960s to produce an empirical standard model of the ionosphere based on all available data sources.

The IRI Working Group consists of more than 60 international experts representing different countries

and different measurement techniques and modelling communities. The group meets annually to

discuss improvements and additions to the model. As a result of these activities several steadily

[18],[19],[20],[5],[6],[1],[2],[3],[53],[72],[73]
improved editions of the model have been released . The homepage

of the IRI project at http://irimodel.org/ provides access to the computer code (FORTRAN) of the latest

version of the model and to earlier versions and to links to several related sites that use IRI for various

applications.

For a given location over the globe, time, and date, IRI describes the monthly averages of electron

+ + + + + +

density, electron temperature, ion temperature, and the percentage of O , H , He , N , NO , O , and

cluster ions in the altitude range from 50 km to 1 500 km. In addition, IRI provides the electron content

by numerically integrating over the electron density height profile within user-provided integral

boundaries. IRI is a climatological model describing monthly average conditions. The major data

sources for building the IRI model are the worldwide network of ionosondes, the powerful incoherent

scatter radars, the topside sounders and in situ instruments flown on several satellites and rockets.

This document also presents several empirical and semi-empirical models that can be used to extend

the IRI model to plasmasphere altitudes.

One advantage of the empirical approach is that it solely depends on measurements and not on the

evolving theoretical understanding of the processes that determine the electron and ion densities

and temperatures in the Earth’s ionosphere. A physical model can help to find the best mathematical

functions to represent variations of these parameters with altitude, latitude, longitude, time of day, day

of year, and solar and magnetic activity.

IRI is recommended for international use by COSPAR and URSI. The IRI model is updated and improved

as new data and new sub-models become available. This document provides a common framework of

the international standard of the Earth’s ionosphere and plasmasphere for the potential users.

© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 16457:2022(E)
Space environment (natural and artificial) — The Earth's
ionosphere model — International reference ionosphere
(IRI) model and extensions to the plasmasphere
1 Scope

This document provides guidance to potential users for the specification of the global distribution of

ionosphere densities and temperatures, as well as the total content of electrons in the height interval

from 50 km to 1 500 km. It includes and explains several options for a plasmaspheric extension of the

model, embracing the geographical area between latitudes of 80°S and 80°N and longitudes of 0°E to

360°E, for any time of day, any day of year, and various solar and magnetic activity conditions.

A brief introduction to ionospheric and plasmaspheric physics is given in Annex A. Annex B provides

an overview over physical models, because they are important for understanding and modelling the

physical processes that produce the ionospheric plasma.
2  Normative references
There are no normative references in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
ionosphere

region of the Earth's atmosphere in the height interval from 50 km to 1 500 km containing weakly

ionized cold plasma
3.2
plasmasphere
−3 +

torus of cold, relatively dense (> 10 cm ) plasma of mostly H in the inner magnetosphere, which is

trapped on the Earth's magnetic field lines and co-rotates with the Earth

Note 1 to entry: Cold plasma is considered to have an energy of between a few electronvolts and a few dozen

electronvolts.
3.3
plasmapause

outward boundary of the plasmasphere (3.2) located at between two and six Earth radii from the centre

of the Earth and formed by geomagnetic field lines where the plasma density drops by a factor of 10 or

more across a range of L-shells of as little as 0,1

Note 1 to entry: The L-shell is a parameter describing a particular set of planetary magnetic field lines, often

describing the set of magnetic field lines which cross the Earth's magnetic equator at a number of Earth-radii

equal to the L-value, e.g. “L = 2” describes the set of the Earth's magnetic field lines which cross the Earth's

magnetic equator two Earth radii from the centre of the Earth.
© ISO 2022 – All rights reserved
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ISO 16457:2022(E)
3.4
solar activity

series of processes occurring in the Sun’s atmosphere which affect the interplanetary space and the

Earth
Note 1 to entry: The level of solar activity is characterized by indices.
3.5
ionospheric storm

storm lasting about a day, documented by depressions and/or enhancements of the ionospheric electron

density during various phases of the storm

Note 1 to entry: Ionospheric storms are the ultimate result of solar flares or coronal mass ejections, which

produce large variations in the particle and electromagnetic radiation that hit Earth's magnetosphere and

ionosphere (3.1), as well as large-scale changes in the global neutral wind, composition and temperature.

3.6
sunspot number

daily index of sunspot activity defined as k(10 g + s) where s is the number of individual spots, g is the

number of sunspot groups, and k is an observatory factor
Note 1 to entry: R is alternatively called Ri or Rz or SSN.
Note 2 to entry: R12 is 12-month running mean of monthly sunspot number.
[68]

Note 3 to entry: In 2014 the calculation scheme for the officially distributed sunspot number was changed

with the result that the new sunspot number (SSN2) is about a factor of 1,45 larger than the old one (SSN1).

3.7
F10.7
solar radio flux at 10,7 cm wavelength measured at the ground daily at noon

Note 1 to entry: Besides this ‘observed’ F10.7 index there is also an ‘adjusted’ F10.7 index that is adjusted to 1AU.

Often used averages are the 81-day (3 solar rotations) running mean and the 12-month running mean.

3.8
Lyman-α index

solar activity (3.4) index based on daily measured solar emission at 121,6 nm (H Lyman-α line)

3.9
MGII index

solar activity (3.4) index based on core-to-wing ratio of the magnesium ion h and k lines at 279,56 nm

and 280,27 nm
3.10
Kp index

planetary three-hour index of geomagnetic activity characterizing the disturbance in the Earth's

[87]
magnetic field over three-hour universal time (UT) intervals

Note 1 to entry: The index scale is uneven quasi-logarithmic and assigned to successive 3 h UT intervals giving

eight values per UT day, and ranges in 28 steps from 0 (quiet) to 9 (disturbed).
3.11
ap index

three-hour UT amplitude index of geomagnetic variation equivalent to the Kp index (3.10)

Note 1 to entry: It is expressed in 1 nT to 400 nT.
© ISO 2022 – All rights reserved
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ISO 16457:2022(E)
3.12
total electron content
TEC

integral number of electrons in the unitary area column from a lower altitude boundary to an upper

boundary

Note 1 to entry: Typically, the integral is taken from the lower boundary of the ionosphere (3.1) to the plasmapause

(3.3)
16 −2
Note 2 to entry: It is expressed in units of 10 electrons m (TECU).
3.13
TECg
TEC-based global index

global ionospheric index based on GNSS-derived TEC-noon measurements at the network of IGS stations

Note 1 to entry: See References [70] and [82] for more information on IGS stations.

3.14
GEC
global electron content

integral of TEC (3.12) over the whole globe based on GNSS-derived TEC measurements

3.15
ionosphere global index
[56] [7]

ionosphere-effective sunspot number (3.6) that is obtained by adjusting the CCIR maps to global

ionosonde measurements of the F2 plasma critical frequency foF2

Note 1 to entry: IG12 is 12-month running mean of monthly ionosphere-effective sunspot number.

Note 2 to entry: See Reference [56] for the ionosphere-effective sunspot number and Reference [7] for the CCIR

maps.
4  Abbreviated terms
ELF extremely low frequency (less than 3 kHz)
BeiDou BeiDou Navigation Satellite System
GALILEO European Global Satellite Navigation System
GLONASS Global Orbiting Navigation Satellite System
GNSS Global Navigation Satellite System (e.g. GPS, GLONASS, GALILEO and others)
GPS Global Positioning System
HF high frequency (3 MHz to 30 MHz)
IRI international reference ionosphere
LF low frequency (30 kHz to 300 kHz)
MF medium frequency (300 kHz to 3 MHz)
UHF ultra high frequency (300 MHz to 3 000 MHz)
VHF very high frequency (30 MHz to 300 MHz)
VLF very low frequency (3 kHz to 30 kHz)
© ISO 2022 – All rights reserved
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ISO 16457:2022(E)
5  General considerations

This model for the representation of the ionospheric and plasmaspheric plasma parameters is important

to a wide spectrum of applications. Electromagnetic waves travelling through the ionized plasma at the

Earth’s environment experience retardation and refraction effects. A remote sensing technique relying

on signals traversing the ionosphere and plasmasphere therefore needs to account for the ionosphere-

plasmasphere influence in its data analysis. Applications can be found in the disciplines of altimetry,

radio astronomy, satellite communication, navigation and orbit determination.

Radio signals, transmitted by modern communication and navigation systems, can be heavily disturbed

by space weather hazards. Thus, severe temporal and spatial changes of the electron density in the

ionosphere and plasmasphere can significantly degrade the signal quality of various radio systems

which even can lead to a complete loss of the signal. Model-based products providing specific space

weather information, in particular now- and fore-cast of the ionospheric state, serve for improvement

of the accuracy and reliability of impacted communication and navigation systems.

For high frequency radio communication, a good knowledge of the heights and plasma frequencies of

the reflective layers of the ionosphere and the plasmasphere is critical for continuous and high-quality

radio reception. High frequency communication remains of great importance in many remote locations

of the globe. The model helps to estimate the effect of charged particles on technical devices in the

Earth's environment and defines the ionosphere-plasmasphere operational environment for existing

and future systems of radio communication, radio navigation, and other relevant radio technologies in

the medium and high frequency ranges.
6 Applicability

There are a multitude of operational usages for ionospheric models, of which the most important are

outlined in this clause. Operators of certain navigational satellite systems such as GPS (USA), GLONASS

(Russia), BeiDou (China) and GALILEO (Europe) require ionospheric predictions to mitigate losses of

navigation signal phase and/or amplitude lock, as well as to maintain accurate orbit determination for

all its satellites. Users of global navigation satellite systems need precise ionospheric models to increase

[57][58]

the accuracy and to reduce the precise positioning convergence time . Radio and television

operators using LF, MF, HF, VHF, UHF satellite or ground stations require ionospheric parameters for

efficient communications and for reducing interferences. Space weather forecasters have a great need

for accurate ionospheric models to support their customers with reliable and up-to-the-minute space

weather information. Ionospheric models are also used in the aeronautical and space system industries

and by governmental agencies performing spacecraft design studies. Here the models help to estimate

surface charging, sensor interference and satellite anomaly conditions.

Users also apply ionospheric models to mitigate problems with HF communications, HF direction

finding, radar clutter and disruption to ELF/VLF communications with underwater vehicles. Insurance

companies estimating the cost of protecting human health in space and satellites make use of

ionospheric models. Scientists using remote sensing measurement techniques in astronomy, biology,

geology, geophysics and seismology require parameter estimates for compensating the effects of the

ionosphere on their observations. An ionospheric model can be also used to evaluate tomographic,

radio occultation, and other similar techniques, by providing the ground-truth background model for

test runs. Amateur radio operators, as well as students and teachers in space research and applications,

also use ionosphere parameters. This document may be also applied for ray-path calculations to assess

the performance of a particular ground-based or space-borne system. Monthly medians of ionospheric

parameters are useful for HF circuit and service planning, while maps for individual days and hours aid

frequency management and retrospective studies.
7  Model description

The first version of the IRI model, IRI-1979, and its mathematical build-up is described in References [18],

[19] and [20]. The most detailed description of the model and the mathematical formulas and methods

[2]

used is given in a 155-page report about IRI-1990 . The next significant updates of the model were

© ISO 2022 – All rights reserved
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ISO 16457:2022(E)
[5] [3] [53],[54] [71],[72] [73]

introduced with IRI-1995 , IRI-2000 , IRI-2007 , IRI-2012 and IRI-2016 . The latest

version of the model is available from http:// irimodel .org.

IRI-related research efforts and applications of the IRI model are presented and discussed during

annual IRI workshops , with each workshop focusing on a specific modelling topic. Papers from these

workshops have been published in dedicated issues of the journal Advances in Space Research .

Reviews of IRI and other ionospheric models can be found in References [4], [51], [52] and [54].

8  Model content and inputs

The IRI model uses a modular approach combining sub-models for the different parameters in different

altitude and/or time regimes. Examples of such sub-models are:

— International Telecommunication Union ITU-R (former CCIR) model for the F2 layer critical

frequency foF2 (directly related with the F2 peak electron density, in m ) and for the propagation

[7]

factor M(3000)F2 (inversely correlated with the peak height, in km) ; IRI recommends use of the

[55]

CCIR model above continental areas and recommends use of the URSI model above ocean areas,

because the URSI model produces better results than the CCIR model in these areas; Instead of the

[56]

CCIR-recommended sunspot number IRI uses the global ionosphere index IG because it gives

better results especially at high solar activities;
[38]

— COSPAR international reference atmosphere (CIRA) model (NRL-MSISE-00 ) for the neutral

temperature;
[9]
— STORM model for storm-time updating of the F2 layer peak density ;

— International geomagnetic reference field (IGRF) model of the International Association of

Geomagnetism and Aeronomy (IAGA) for the magnetic coordinates (https:// www .ngdc .noaa .gov/

IAGA/ vmod/ ).
The IRI model requires the following indices as input parameters:
— R12, the 12-month running mean of sunspot number R;
— F10.7, the daily index and 81-day and 12-month running mean;
— IG12, the 12-month running mean of global ionosphere index IG;
— ap indices, the 3-hourly planetary magnetic indices for the prior 33 hours.

These indices can either be found automatically from the indices files that are included with the IRI

software package and that are updated quarterly, or the user can provide his/her own input values for

these indices. For R12 and IG12, the indices file starts from January 1958 and include indices prediction

for one to two years into the future. For ap index, the values start from January 1960 and include no

predictions.

In addition, model users have the options to use measured peak parameters to update the IRI profile,

including the F2, F1, and E layer critical frequencies (or electron densities), the F2 peak height (or

M(3000)F2 propagation factor), the E peak height, and the bottomside thickness and shape parameters

B0 and B1. In this way, real-time IRI predictions can be obtained if the real-time peak parameters are

available.

The total electron content (TEC) is obtained by numerical integration from the model’s lower boundary

(65 km during daytime and 80 km during night time) to the user-specified upper boundary.

1) Information about past and future workshops can be found on the IRI homepage (http:// irimodel .org), which

also provides access to the final report from each workshop and to a bibliography of IRI-related papers and issues

of Advances in Space Research.

2) A list of IRI issues of Advances in Space Research is available at http:// irimodel .org/ docs/ asr _list .html.

© ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 16457:2022(E)
9  Real-time IRI

Various data-assimilation techniques and indices-updating algorithms have been used to bring IRI

[74]-[81]

closer to the observed conditions in either real-time or retrospective mode . The most advanced

[79]

system developed by Galkin et al. uses the global database of ionosonde measurements of the Global

Ionospheric Radio Observatory (GIRO) to provide real-time inputs of foF2, hmF2, B0 and B1 for IRI.

10 Plasmasphere extension of the IRI model
10.1 General

The models described in 10.2 to 10.5 have been proposed as plasmasphere extension of the IRI model.

10.2 Extrapolation of IRI profiles

With the version of the IRI model available at http:// irimodel .org, a user is given the option to increase

the upper boundary for TEC computations to up to 20 000 km (GPS satellite altitude). Above 2 000 km a

simple extrapolation is used employing the IRI topside function.
10.3 Global core plasma model (GCPM)
[10]

GCPM-2000 is an empirical description of thermal plasma densities in the plasmasphere,

plasmapause, magnetospheric trough and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI

in the transition region 500 km to 600 km .
10.4 IMAGE/RPI plasmasphere model
[15]

The IMAGE/RPI plasmasphere model is based on more than 700 density profiles along field lines

[21]

derived from active sounding measurements made by the radio plasma imager (RPI) on the

IMAGE satellite between June 2000 and July 2005. The measurements cover all magnetic local times

and vary from L = 1,6 to L = 4 spatially. The resulting model depends not only on L-shell but also on

magnetic latitude and can be applied to specify the electron densities in the plasmasphere between

2 000 km altitude and the plasmapause (the plasmapause location itself is not included in this model).

A comparison of this model with other diffusive equilibrium models was published in Reference [22]. A

power profile model as function of magnetic activity was developed from RPI observations for the polar

[17]
cap region .
10.5 IZMIRAN plasmasphere model
4) [8],[11],[13]

The IZMIRAN plasmasphere model is an empirical model based on whistler and satellite

observations. IRI-Plas model presents global vertical analytical profiles of electron density and

temperature in the plasmasphere smoothly fitted to the IRI Ne(h) and Te(h) profiles at the altitude of the

topside half peak density (400 km to 600 km for electron density and 400 km for electron temperature)

and extended towards the plasmapause (up to 36 000 km). For the smooth fitting of the two models,

the shape of the IRI topside electron density profile is modified using ISIS-1, ISIS-2 and IK-19 satellite

[12]

inputs . The plasmasphere model depends on solar activity and magnetic activity. The latest version

of IRI-Plas model includes dependence on eight solar and ionospheric proxy indices (SSN, R12, F10.7,

3) A FORTRAN code implementation of GCPM that includes all regions except the polar cap is

...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 16457
ISO/TC 20/SC 14
Space environment (natural and
Secretariat: ANSI
artificial) — The Earth's ionosphere
Voting begins on:
2021-10-29 model — International reference
ionosphere (IRI) model and
Voting terminates on:
2021-12-24
extensions to the plasmasphere
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 16457:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 16457:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 16457:2021(E)
Contents  Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2  Normative references ..................................................................................................................................................................................... 1

3  Terms and definitions .................................................................................................................................................................................... 1

4  Abbreviated terms ............................................................................................................................................................................................. 3

5  General considerations .................................................................................................................................................................................4

6 Applicability.............................................................................................................................................................................................................. 4

7  Model description ...............................................................................................................................................................................................4

8  Model content and inputs ........................................................................................................................................................................... 5

9  Real-time IRI ............................................................................................................................................................................................................ 6

10  Plasmasphere extension of the IRI model ................................................................................................................................ 6

10.1 General ........................................................................................................................................................................................................... 6

10.2 Extrapolation of IRI profiles ....................................................................................................................................................... 6

10.3 Global core plasma model (GCPM) ........................................................................................................................................ 6

10.4 IMAGE/RPI plasmasphere model........................................................................................................................................... 6

10.5 IZMIRAN plasmasphere model ................................................................................................................................................ 6

11  Accuracy of the model ....................................................................................................................................................................................7

Annex A (informative) Brief introduction to ionosphere and plasmasphere physics ....................................8

Annex B (informative) Physical models ........................................................................................................................................................... 9

Bibliography .............................................................................................................................................................................................................................13

iii
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ISO/FDIS 16457:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 14, Space systems and operations.

This second edition cancels and replaces the first edition (ISO 16457:2014), which has been technically

revised.
The main changes are as follows:
— adding a description of the newly developed real-time IRI (Clause 8);

— replacing one of the plasmaspheric extension models (GPID) that is no longer available with the

option to extrapolate the standard IRI to plasmaspheric altitudes;

— providing more detail and newer references for the IMAGE/RPI and IZMIRAN plasmaspheric

extensions of IRI.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/FDIS 16457:2021(E)
Introduction

The purpose of this document is to identify a set of management guidelines for dealing with space

systems engineering activities and is intended to define the minimum existing processes on the subject

seeking to reach an international agreement on the topic.

Guided by the knowledge gained from empirical data analysis, this document provides guidelines

for specifying the global distribution of electron density, electron temperature, ion temperature,

ion composition, and total electron content through the Earth’s ionosphere and plasmasphere. The

model recommended for the representation of these parameters in the ionosphere is the international

reference ionosphere (IRI).

IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the

International Union of Radio Science (URSI). These organizations formed a working group in the late

1960s to produce an empirical standard model of the ionosphere based on all available data sources.

The IRI Working Group consists of more than 60 international experts representing different countries

and different measurement techniques and modelling communities. The group meets annually to

discuss improvements and additions to the model. As a result of these activities several steadily

[18],[19],[20],[5],[6],[1],[2],[3],[53],[72],[73]
improved editions of the model have been released . The homepage

of the IRI project at http://irimodel.org/ provides access to the computer code (FORTRAN) of the latest

version of the model and to earlier versions and to links to several related sites that use IRI for various

applications.

For a given location over the globe, time, and date, IRI describes the monthly averages of electron

+ + + + + +

density, electron temperature, ion temperature, and the percentage of O , H , He , N , NO , O , and

cluster ions in the altitude range from 50 km to 1 500 km. In addition, IRI provides the electron content

by numerically integrating over the electron density height profile within user-provided integral

boundaries. IRI is a climatological model describing monthly average conditions. The major data

sources for building the IRI model are the worldwide network of ionosondes, the powerful incoherent

scatter radars, the topside sounders and in situ instruments flown on several satellites and rockets.

This document also presents several empirical and semi-empirical models that can be used to extend

the IRI model to plasmasphere altitudes.

One advantage of the empirical approach is that it solely depends on measurements and not on the

evolving theoretical understanding of the processes that determine the electron and ion densities

and temperatures in the Earth’s ionosphere. A physical model can help to find the best mathematical

functions to represent variations of these parameters with altitude, latitude, longitude, time of day, day

of year, and solar and magnetic activity.

IRI is recommended for international use by COSPAR and URSI. The IRI model is updated and improved

as new data and new sub-models become available. This document provides a common framework of

the international standard of the Earth’s ionosphere and plasmasphere for the potential users.

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 16457:2021(E)
Space environment (natural and artificial) — The Earth's
ionosphere model — International reference ionosphere
(IRI) model and extensions to the plasmasphere
1 Scope

This document provides guidance to potential users for the specification of the global distribution of

ionosphere densities and temperatures, as well as the total content of electrons in the height interval

from 50 km to 1 500 km. It includes and explains several options for a plasmaspheric extension of the

model, embracing the geographical area between latitudes of 80°S and 80°N and longitudes of 0°E to

360°E, for any time of day, any day of year, and various solar and magnetic activity conditions.

A brief introduction to ionospheric and plasmaspheric physics is given in Annex A. Annex B provides

an overview over physical models, because they are important for understanding and modelling the

physical processes that produce the ionospheric plasma.
2  Normative references
There are no normative references in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
ionosphere

region of the Earth's atmosphere in the height interval from 50 km to 1 500 km containing weakly

ionized cold plasma
3.2
plasmasphere
−3 +

torus of cold, relatively dense (> 10 cm ) plasma of mostly H in the inner magnetosphere, which is

trapped on the Earth's magnetic field lines and co-rotates with the Earth

Note 1 to entry: Cold plasma is considered to have an energy of between a few electronvolts and a few dozen

electronvolts.
3.3
plasmapause

outward boundary of the plasmasphere (3.2) located at between two and six Earth radii from the centre

of the Earth and formed by geomagnetic field lines where the plasma density drops by a factor of 10 or

more across a range of L-shells of as little as 0,1

Note 1 to entry: The L-shell is a parameter describing a particular set of planetary magnetic field lines, often

describing the set of magnetic field lines which cross the Earth's magnetic equator at a number of Earth-radii

equal to the L-value, e.g. “L = 2” describes the set of the Earth's magnetic field lines which cross the Earth's

magnetic equator two Earth radii from the centre of the Earth.
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ISO/FDIS 16457:2021(E)
3.4
solar activity

series of processes occurring in the Sun’s atmosphere which affect the interplanetary space and the

Earth
Note 1 to entry: The level of solar activity is characterized by indices.
3.5
ionospheric storm

storm lasting about a day, documented by depressions and/or enhancements of the ionospheric electron

density during various phases of the storm

Note 1 to entry: Ionospheric storms are the ultimate result of solar flares or coronal mass ejections, which

produce large variations in the particle and electromagnetic radiation that hit Earth's magnetosphere and

ionosphere (3.1), as well as large-scale changes in the global neutral wind, composition and temperature.

3.6
sunspot number

daily index of sunspot activity defined as k(10 g + s) where s is the number of individual spots, g is the

number of sunspot groups, and k is an observatory factor
Note 1 to entry: R is alternatively called Ri or Rz or SSN.
Note 2 to entry: R12 is 12-month running mean of monthly sunspot number.
[68]

Note 3 to entry: In 2014 the calculation scheme for the officially distributed sunspot number was changed

with the result that the new sunspot number (SSN2) is about a factor of 1,45 larger than the old one (SSN1).

3.7
F10.7
solar radio flux at 10,7 cm wavelength measured at the ground daily at noon

Note 1 to entry: Besides this ‘observed’ F10.7 index there is also an ‘adjusted’ F10.7 index that is adjusted to 1AU.

Often used averages are the 81-day (3 solar rotations) running mean and the 12-month running mean.

3.8
Lyman-α index

solar activity (3.4) index based on daily measured solar emission at 121,6 nm (H Lyman-α line)

3.9
MGII index

solar activity (3.4) index based on core-to-wing ratio of the magnesium ion h and k lines at 279,56 nm

and 280,27 nm
3.10
Kp index

planetary three-hour index of geomagnetic activity characterizing the disturbance in the Earth's

[87]
magnetic field over three-hour universal time (UT) intervals

Note 1 to entry: The index scale is uneven quasi-logarithmic and assigned to successive 3 h UT intervals giving

eight values per UT day, and ranges in 28 steps from 0 (quiet) to 9 (disturbed).
3.11
ap index

three-hour UT amplitude index of geomagnetic variation equivalent to the Kp index (3.10)

Note 1 to entry: It is expressed in 1 nT to 400 nT.
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ISO/FDIS 16457:2021(E)
3.12
total electron content
TEC

integral number of electrons in the unitary area column from a lower altitude boundary to an upper

boundary

Note 1 to entry: Typically, the integral is taken from the lower boundary of the ionosphere (3.1) to the plasmapause

(3.3)
16 −2
Note 2 to entry: It is expressed in units of 10 electrons m (TECU).
3.13
TECg
TEC-based global index

global ionospheric index based on GNSS-derived TEC-noon measurements at the network of IGS stations

Note 1 to entry: See References [70] and [82] for more information on IGS stations.

3.14
GEC
global electron content

integral of TEC (3.12) over the whole globe based on GNSS-derived TEC measurements

3.15
ionosphere global index
[56] [7]

ionosphere-effective sunspot number (3.6) that is obtained by adjusting the CCIR maps to global

ionosonde measurements of the F2 plasma critical frequency foF2

Note 1 to entry: IG12 is 12-month running mean of monthly ionosphere-effective sunspot number.

Note 2 to entry: See Reference [56] for the ionosphere-effective sunspot number and Reference [7] for the CCIR

maps.
4  Abbreviated terms
ELF extremely low frequency (less than 3 kHz)
BeiDou BeiDou Navigation Satellite System
GALILEO European Global Satellite Navigation System
GLONASS Global Orbiting Navigation Satellite System
GNSS Global Navigation Satellite System (e.g. GPS, GLONASS, GALILEO and others)
GPS Global Positioning System
HF high frequency (3 MHz to 30 MHz)
IRI international reference ionosphere
LF low frequency (30 kHz to 300 kHz)
MF medium frequency (300 kHz to 3 MHz)
UHF ultra high frequency (300 MHz to 3 000 MHz)
VHF very high frequency (30 MHz to 300 MHz)
VLF very low frequency (3 kHz to 30 kHz)
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ISO/FDIS 16457:2021(E)
5  General considerations

This model for the representation of the ionospheric and plasmaspheric plasma parameters is important

to a wide spectrum of applications. Electromagnetic waves travelling through the ionized plasma at the

Earth’s environment experience retardation and refraction effects. A remote sensing technique relying

on signals traversing the ionosphere and plasmasphere therefore needs to account for the ionosphere-

plasmasphere influence in its data analysis. Applications can be found in the disciplines of altimetry,

radio astronomy, satellite communication, navigation and orbit determination.

Radio signals, transmitted by modern communication and navigation systems, can be heavily disturbed

by space weather hazards. Thus, severe temporal and spatial changes of the electron density in the

ionosphere and plasmasphere can significantly degrade the signal quality of various radio systems

which even can lead to a complete loss of the signal. Model-based products providing specific space

weather information, in particular now, and forecast of the ionospheric state, serve for improvement of

the accuracy and reliability of impacted communication and navigation systems.

For high frequency radio communication, a good knowledge of the heights and plasma frequencies of

the reflective layers of the ionosphere and the plasmasphere is critical for continuous and high-quality

radio reception. High frequency communication remains of great importance in many remote locations

of the globe. The model helps to estimate the effect of charged particles on technical devices in the

Earth's environment and defines the ionosphere-plasmasphere operational environment for existing

and future systems of radio communication, radio navigation, and other relevant radio technologies in

the medium and high frequency ranges.
6 Applicability

There are a multitude of operational usages for ionospheric models, of which the most important are

outlined in this clause. Operators of certain navigational satellite systems such as GPS (USA), GLONASS

(Russia), BeiDou (China) and GALILEO (Europe) require ionospheric predictions to mitigate losses of

navigation signal phase and/or amplitude lock, as well as to maintain accurate orbit determination for

all its satellites. Users of global navigation satellite systems need precise ionospheric models to increase

[57][58]

the accuracy and to reduce the precise positioning convergence time . Radio and television

operators using LF, MF, HF, VHF, UHF satellite or ground stations require ionospheric parameters for

efficient communications and for reducing interferences. Space weather forecasters have a great need

for accurate ionospheric models to support their customers with reliable and up-to-the-minute space

weather information. Ionospheric models are also used in the aeronautical and space system industries

and by governmental agencies performing spacecraft design studies. Here the models help to estimate

surface charging, sensor interference and satellite anomaly conditions.

Users also apply ionospheric models to mitigate problems with HF communications, HF direction

finding, radar clutter and disruption to ELF/VLF communications with underwater vehicles. Insurance

companies estimating the cost of protecting human health in space and satellites make use of

ionospheric models. Scientists using remote sensing measurement techniques in astronomy, biology,

geology, geophysics and seismology require parameter estimates for compensating the effects of the

ionosphere on their observations. An ionospheric model can be also used to evaluate tomographic,

radio occultation, and other similar techniques, by providing the ground-truth background model for

test runs. Amateur radio operators, as well as students and teachers in space research and applications,

also use ionosphere parameters. This document may be also applied for ray-path calculations to assess

the performance of a particular ground-based or space-borne system. Monthly medians of ionospheric

parameters are useful for HF circuit and service planning, while maps for individual days and hours aid

frequency management and retrospective studies.
7  Model description

The first version of the IRI model, IRI-1979, and its mathematical build-up is described in References [18],

[19] and [20]. The most detailed description of the model and the mathematical formulas and methods

[2]

used is given in a 155-page report about IRI-1990 . The next significant updates of the model were

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ISO/FDIS 16457:2021(E)
[5] [3] [53],[54] [71],[72] [73]

introduced with IRI-1995 , IRI-2000 , IRI-2007 , IRI-2012 and IRI-2016 . The latest

version of the model is available from http:// irimodel .org.

IRI-related research efforts and applications of the IRI model are presented and discussed during

annual IRI workshops , with each workshop focusing on a specific modelling topic. Papers from these

workshops have been published in dedicated issues of the journal Advances in Space Research .

Reviews of IRI and other ionospheric models can be found in References [4], [51], [52] and [54].

8  Model content and inputs

The IRI model uses a modular approach combining sub-models for the different parameters in different

altitude and/or time regimes. Examples of such sub-models are:

— International Telecommunication Union ITU-R (former CCIR) model for the F2 layer critical

frequency foF2 (directly related with the F2 peak electron density, in m ) and for the propagation

[7]

factor M(3000)F2 (inversely correlated with the peak height, in km) ; IRI recommends use of the

[55]

CCIR model above continental areas and recommends use of the URSI model above ocean areas,

because the URSI model produces better results than the CCIR model in these areas; Instead of the

[56]

CCIR-recommended sunspot number IRI uses the global ionosphere index IG because it gives

better results especially at high solar activities;
[38]

— COSPAR international reference atmosphere (CIRA) model (NRL-MSISE-00 ) for the neutral

temperature;
[9]
— STORM model for storm-time updating of the F2 layer peak density ;

— international geomagnetic reference field (IGRF) model of the International Association of

Geomagnetism and Aeronomy (IAGA) for the magnetic coordinates (https:// www .ngdc .noaa .gov/

IAGA/ vmod/ ).
The IRI model requires the following indices as input parameters:
— R12, the 12-month running mean of sunspot number R;
— F10.7, the daily index and 81-day and 12-month running mean;
— IG12, the 12-month running mean of global ionosphere index IG;
— ap indices, the 3-hourly planetary magnetic indices for the prior 33 hours.

These indices can either be found automatically from the indices files that are included with the IRI

software package and that are updated quarterly, or the user can provide his/her own input values for

these indices. For R12 and IG12, the indices file starts from January 1958 and include indices prediction

for one to two years into the future. For ap index, the values start from January 1960 and include no

predictions.

In addition, model users have the options to use measured peak parameters to update the IRI profile,

including the F2, F1, and E layer critical frequencies (or electron densities), the F2 peak height (or

M(3000)F2 propagation factor), the E peak height, and the bottomside thickness and shape parameters

B0 and B1. In this way, real-time IRI predictions can be obtained if the real-time peak parameters are

available.

The total electron content (TEC) is obtained by numerical integration from the model’s lower boundary

(65 km during daytime and 80 km during night time) to the user-specified upper boundary.

1) Information about past and future workshops can be found on the IRI homepage (http:// irimodel .org), which

also provides access to the final report from each workshop and to a bibliography of IRI-related papers and issues

of Advances in Space Research.

2) A list of IRI issues of Advances in Space Research is available at http:// irimodel .org/ docs/ asr _list .html.

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ISO/FDIS 16457:2021(E)
9  Real-time IRI

Various data-assimilation techniques and indices-updating algorithms have been used to bring IRI

[74]-[81]

closer to the observed conditions in either real-time or retrospective mode . The most advanced

[79]

system developed by Galkin et al. uses the global database of ionosonde measurements of the Global

Ionospheric Radio Observatory (GIRO) to provide real-time inputs of foF2, hmF2, B0 and B1 for IRI.

10 Plasmasphere extension of the IRI model
10.1 General

The models described in 10.2 to 10.5 have been proposed as plasmasphere extension of the IRI model.

10.2 Extrapolation of IRI profiles

With the latest version of the IRI model (available at http:// irimodel .org) a user is now given the option

to increase the upper boundary for TEC computations to up to 20 000 km (GPS satellite altitude). Above

2 000 km a simple extrapolation is used employing the IRI topside function.
10.3 Global core plasma model (GCPM)
[10]

GCPM-2000 is an empirical description of thermal plasma densities in the plasmasphere,

plasmapause, magnetospheric trough and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI

in the transition region 500 km to 600 km .
10.4 IMAGE/RPI plasmasphere model
[15]

The IMAGE/RPI plasmasphere model is based on more than 700 density profiles along field lines

[21]

derived from active sounding measurements made by the radio plasma imager (RPI) on the

IMAGE satellite between June 2000 and July 2005. The measurements cover all magnetic local times

and vary from L = 1,6 to L = 4 spatially. The resulting model depends not only on L-shell but also on

magnetic latitude and can be applied to specify the electron densities in the plasmasphere between

2 000 km altitude and the plasmapause (the plasmapause location itself is not included in this model).

A comparison of this model with other diffusive equilibrium models was published in Reference [22]. A

power profile model as function of magnetic activity was developed from RPI observations for the polar

[17]
cap region .
10.5 IZMIRAN plasmasphere model
4) [8],[11],[13]

The IZMIRAN plasmasphere model is an empirical model based on whistler and satellite

observations. IRI-Plas model presents global vertical analytical profiles of electron density and

temperature in the plasmasphere smoothly fitted to the IRI Ne(h) and Te(h) profiles at the altitude of the

topside half peak density (400 km to 600 km for electron density and 400 km for electron temperature)

and extended towards the plasmap
...

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