Extraterrestrial Influences on Remote Sensing in the Earth’s Atmosphere

Abstract

Atmospheric properties have a significant influence on electromagnetic (EM) waves, including the propagation of EM signals used for remote sensing. For this reason, changes in the received amplitudes and phases of these signals can be used for the detection of the atmospheric disturbances and, consequently, for their investigation. Some of the most important sources of the temporal and space variations in the atmospheric parameters come from the outer space. Although the solar radiation dominates in these processes, radiation coming out of the solar system also can induces enough intensive disturbance in the atmosphere to provide deflections in the EM signal propagation paths. The aim of this issue is to present the latest research linking events and processes in outer space with changes in the propagation of the satellite and ground-based signals used in remote sensing.

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remote sensing
Editorial
Extraterrestrial Influences on Remote Sensing in the
Earth’s Atmosphere
Aleksandra Nina 1,* , Milan Radovanovi´c 2,3 and Luka ˇ
C. Popovi´c 4,5,6


Citation: Nina, A.; Radovanovi´c, M.;
Popovi´c, L. ˇ
C. Extraterrestrial
Influences on Remote Sensing in the
Earth’s Atmosphere. Remote Sens.
2021,13, 890.
https://doi.org/10.3390/rs13050890
Received: 17 February 2021
Accepted: 22 February 2021
Published: 26 February 2021
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1Institute of Physics Belgrade, University of Belgrade, 11080 Belgrade, Serbia
2Geographical Institute “Jovan Cviji´c” SASA, 11000 Belgrade, Serbia; m.radovanovic@gi.sanu.ac.rs
3Institute of Sports, Tourism and Service, South Ural State University, 454080 Chelyabinsk, Russia;
milan.georgaf@gmail.com
4Astronomical Observatory, 11060 Belgrade, Serbia; lpopovic@aob.rs
5Department of Astronomy, Faculty of mathematics, University of Belgrade, 11000 Belgrade, Serbia;
lpopovic@matf.bg.ac.rs
6Faculty of Science, University of Banja Luka, 78000 Banja Luka, R. Srpska, Bosnia and Herzegovina;
luka.popovic@pmg.unibl.org
*Correspondence: sandrast@ipb.ac.rs
Abstract:
Atmospheric properties have a significant influence on electromagnetic (EM) waves,
including the propagation of EM signals used for remote sensing. For this reason, changes in the
received amplitudes and phases of these signals can be used for the detection of the atmospheric
disturbances and, consequently, for their investigation. Some of the most important sources of the
temporal and space variations in the atmospheric parameters come from the outer space. Although
the solar radiation dominates in these processes, radiation coming out of the solar system also can
induces enough intensive disturbance in the atmosphere to provide deflections in the EM signal
propagation paths. The aim of this issue is to present the latest research linking events and processes
in outer space with changes in the propagation of the satellite and ground-based signals used in
remote sensing.
Keywords:
atmosphere; observations; signal processing; modelling; extraterrestrial radiation; solar
radiation; disturbances; remote sensing
1. Introduction
As the highest terrestrial layer, the atmosphere is under permanent influences from
outer space. For this reason and due to link with many processes in different areas of Earth,
the temporal and space distributions of atmospheric parameters are very complex and
have been the focus of a number of studies in different research fields. The application of
these studies is important for pure sciences but also for applied sciences and technology.
Since the measurement of atmospheric parameters using on-site methods is very
complex, remote sensing has very important role in observations of different-altitude
domains. The propagation properties of a signal which have been used for different
kinds of remote sensing depend on the different atmospheric parameters, such as the
electron density and temperature. The spatial and temporal variations in these parameters
affect signal propagations and, consequently, the corresponding applications of the used
technique, such as observations and positioning. Some of the most important sources
of atmospheric disturbances are solar wind and radiation. In addition, cosmic rays can
provide intensive perturbations of the outer Earth’s layer [
1
–
3
]. The perturbation intensity,
duration, and location in the Earth’s atmosphere can be quite different, which can induce
various signal deviations.
The focus of this Special Issue is: (1) the detection of extraterrestrial events and induced
atmospheric disturbance modelling, and (2) the influences of atmospheric parameter
variations on EM signal propagation.
Remote Sens. 2021,13, 890. https://doi.org/10.3390/rs13050890 https://www.mdpi.com/journal/remotesensing

Remote Sens. 2021,13, 890 2 of 4
2. Extraterrestrial Influences on the Earth Atmosphere—Remote Sensing
of Disturbances
The properties of the atmospheric disturbances induced by extraterrestrial events
and processes depend on the characteristics of the disturbance sources (intensities, source
type etc.), the considered atmospheric area (due to interaction of incoming radiation or
bodies with particles within them), and the space between them (due to the interaction of
incoming radiation or bodies with the atmosphere part before its arrival at the considered
location). Charged particlesprimarily disturb the upper ionosphere as well as the polar and
near-polar latitudes (due to the geomagnetic field), while the influence of the EM radiation
depends on the radiation intensity, wavelength, impact angle in the atmosphere, and the
area within its propagation.
These variations can be periodical because of, for example, variations during a solar
cycle, year (due to Earth’s revolution), and day (due to Earth’s rotation), and sudden due
to expected or unexpected outer space phenomena (see Figure 1). The periodical changes
in the atmospheric parameters and the precision of their determination are primarily
connected with the solar radiation. They are recorded within all atmospheric layers,
from the ionosphere and magnetosphere in the upper atmosphere [
4
–
6
] to the troposphere
and stratosphere in the lower atmosphere [
7
]. The sources of these sudden perturbations
can be the Sun, solar system, galaxy, or the wider Universe [
3
,
8
]. The intensity and duration
of their influences on the atmosphere are different: from very weak and very hard to detect
to extremely intensive when the atmospheric parameters are changed by several orders
of magnitude [
9
,
10
], and from short-lasting (several milliseconds) [
2
] to perturbations of
several days or more [11].
Figure 1.
Scheme of outer space’s influence on the Earth’s atmosphere. Extraterrestrial electromag-
netic and particle radiation coming from the Sun, our galaxy, and the wider universe, and impact
of meteors in the Earth’s atmosphere. Several examples of the remote sensing of the atmosphere:
troposphere observations by LIDAR, VLF/LF signal monitoring of the lower ionosphere, ionospheric
monitoring using signals emitted by ionosondes, satellite observations.
The application of an observation technique depends on the considered altitude
domain. In addition, the detection of the short-term variations requires the good temporal

Remote Sens. 2021,13, 890 3 of 4
resolution of the observed data, while the monitoring of the unpredictable phenomena is
possible with continuous measurements provided by, for example, the Global Navigation
Satellite System (GNSS) [
12
] or lower ionosphere monitoring by very low/low frequency
radio waves [2,3,13,14].
The recorded data are included in many methodologies for the modelling of the
spatial and temporal distributions of atmospheric parameters. In some cases, their esti-
mation within a local area requirea more then one data set and more than one monitoring
techniques [15–17]m which provides more precious estimates of atmospheric properties.
3. Extraterrestrial Influences on Electromagnetic Signal Propagation
The investigation of the signal propagation changes induced by extraterrestrial events
and processes, primarily with origins in the solar system, is very important due to possible
errors in their use in observations and modelling. This task can be crucial for precision in
technologies based on, for example, satellite signal propagation, which is reason why the
corresponding research took place many decades ago and why it is still of high importance.
In this field, solar radiation is the subject of most relevant studies. Its influence on
satellite signals dominates in the upper ionosphere due to the largest electron density in
this atmospheric layer, which is often used as an approximation in the estimation of the
total electron content (TEC), the ionospheric parameter required in the modelling of signal
propagation [
18
–
20
]. However, the recent study presented in [
21
] shows that errors due to
the neglect of the D-region electron density increase induced by a solar X-ray flare can be
important for the precision of satellite signal propagation modelling. Lower ionosphere
disturbances as well as F-region disturbances below the altitude of the electron density
maximum are important for the propagation of ground-based signals emitted at the surface
and reflected from the ionosphere. A well-known example of extreme solar radiation
influence on radio signal propagation is black out [22].
The influence of the Solar radiation on the quality of signals is also reported in lower
atmospheric observations. As an example, in [
23
] the authors analysed solar radiation’s
influence on error in temperature measurements.
4. Summary
The main goal of this Special Issue is to collect studies about extraterrestrial influences
on remote sensing in the Earth’s atmosphere. Attention is focused on research on the
following topics:
•
The detection of extra-terrestrial radiation and the modelling of the induced atmo-
spheric disturbances using different kinds of remote sensing techniques;
•
Changes in signals used for remote sensing and the quality of their applications during
influences of extra-terrestrial events;
•
Influence of events from outer space on the detection of terrestrial or extra-terrestrial
events and corresponding modelling, such as masking less intense perturbations with
solar influences;
•
The Earth’s atmosphere’s perturbations due to extra-terrestrial events (e.g., meteor
perturbations) that may affect signal propagation, etc.
Studies in different research fields should emphasise the multidisciplinary character
of both observations and modelling corresponding to extraterrestrial influences on remote
sensing in the Earth’s atmosphere
Author Contributions:
Conceptualization, original draft preparation, and visualization, A.N.; review
and editing, all authors. All authors have read and agreed to the published version of the manuscript.
Funding:
The authors acknowledge funding provided by the Institute of Physics Belgrade and
the Astronomical Observatory (the contract 451-03-68/2020-14/200002) through the grants by the
Ministry of Education, Science, and Technological Development of the Republic of Serbia.

Remote Sens. 2021,13, 890 4 of 4
Acknowledgments:
The authors thank to Zoran Miji´c and Nikola Veselinovi´c for help in preparation
of this paper, and Sr ¯
dan Mitrovi´c for help in promotion of this Special Issue. We also would like to
thank the Remote Sensing editorial team for its support in preparation of this SI.
Conflicts of Interest: The authors declare no conflict of interest.
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