The ionosphere is composed of two main layers: the lower layer, which has been designated as layer E and is sometimes also known as Heaviside or Kennelly-Heaviside layer and is located between 80 and 112 km above the Earth’s surface reflecting low-frequency radio waves; and the upper layer, also known as F or Appleton layer, which reflects higher frequency radio waves. Ionograms show the virtual heights and critical frequencies of the ionospheric layers and which are measured by an ionosonde. The ionosphere (/aɪˈɒnəˌsfɪər/) is the ionized part of Earth's upper atmosphere, from about 48 km (30 mi) to 965 km (600 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. Both are valuable for their long historical records covering multiple solar cycles. f = frequency of operation (Hz). Ionization depends primarily on the Sun and its activity. The thermosphere rises several hundred miles above the Earth's surface, from 56 miles (90 km) up to between 311 and 621 miles (500–1,000 km). The ionosphere can be categorised into a number of regions corresponding to peaks in the electron density. These investigations focus on studying the properties and behavior of ionospheric plasma, with particular emphasis on being able to understand and use it to enhance communications and surveillance systems for both civilian and military purposes. As a result the way in which the E layer or E region acts is somewhat different. The activity of the Sun modulates following the solar cycle, with more radiation occurring with more sunspots, with a periodicity of around 11 years. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring the ionosphere. As a result the figures given should only be taken as a rough guide. The geomagnetic activity levels of the Earth are measured by the fluctuation of the Earth's magnetic field in, This page was last edited on 27 October 2020, at 02:04. Propagation software Above that is the stratosphere, followed by the mesosphere. Vertical antennas It is calculated as shown below: where N = electron density per m3 and fcritical is in Hz. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere. At heights of above 80 km (50 mi), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. As the signal is travelling in an area where the density of electrons is increasing, the further it progresses into the region, the signal is refracted away from the area of higher electron density. The F layer consists of one layer (F2) at night, but during the day, a secondary peak (labelled F1) often forms in the electron density profile. Therefore, the technique allows probing the ionosphere, unlike ionosondes, also above the electron density peaks.