An ionosonde, or chirpsounder, is a special radar for the examination of the ionosphere. The basic ionosonde technology was invented in 1925 by Gregory Breit and Merle A. Tuve [1] and further developed in the late 1920s by a number of prominent physicists, including Edward Victor Appleton. The term ionosphere and hence, the etymology of its derivatives, was proposed by Robert Watson-Watt.
An ionosonde consists of:
The transmitter sweeps all or part of the HF frequency range, transmitting short pulses. These pulses are reflected at various layers of the ionosphere, at heights of 100–400 km (60 to 250 miles), and their echos are received by the receiver and analyzed by the control system. The result is displayed in the form of an ionogram, a graph of reflection height (actually time between transmission and reception of pulse) versus carrier frequency.
An ionosonde is used for finding the optimum operation frequencies for broadcasts or two-way communications in the high frequency range.
An ionogram is a display of the data produced by an ionosonde; technically speaking one may call the data used to make the display as the ionogram but often this is simply implied. It is a graph of the virtual height of the ionosphere plotted against frequency. Ionograms are often converted into electron density profiles. Data from ionograms may be used to measure changes in the Earth's ionosphere due to space weather events.
Note that in the ionogram above the legend can be more clearly understood as having "Vx-" and "Vx+" to replace respectively "X-" and "X+". These refer to the vertical reflection of the eXtraordinary kind. "Vo-" and "Vo+" refer to the Ordinary reflection. An Ordinarily reflected wave is the one that behaves as though there were no geomagnetic field.
ARTIST is the software program used to "scale" (deduce or calculate) the characteristic parameter values shown in the table on the left. The version shown here is "5", which is the latest as of March 2022. Ion2Png is the software program used to create the ionogram image.
A chirp transmitter is a shortwave radio transmitter that sweeps the HF radio spectrum on a regular schedule. If one is monitoring a specific frequency, then a chirp is heard (in CW or SSB mode) when the signal passes through. In addition to their use in probing ionospheric properties, [2] these transmitters are also used for over-the-horizon radar systems. [3]
An analysis of existing transmitters has been done using SDR technology. [4] For better identification of chirp transmitters the following notation is used: <repetition rate (s)>:<chirp offset (s)>, where the repetition rate is the time between two sweeps in seconds and the chirp offset is the time of the first sweep from 0 MHz after a full hour in seconds. If the initial frequency is greater than 0 MHz, the offset time can be linearly extrapolated to 0 MHz. [2]
The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth. It also affects GPS signals that travel through this layer.
Ground waves are radio waves propagating parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. This radiation is known as Norton surface wave, or more properly Norton ground wave, because ground waves in radio propagation are not confined to the surface.
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz ; above the medium frequency band (MF), to the bottom of the VHF band.
The High-frequency Active Auroral Research Program (HAARP) is a University of Alaska Fairbanks program which researches the ionosphere - the highest, ionized part of Earth's atmosphere.
Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band as the wavelengths range from ten to one hectometers. Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.
High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.
The Ionosonde Juliusruh is a facility of the institute for atmospheric physics near Juliusruh in northeastern Germany for sounding the ionosphere with radar systems in the short wave range. The landmark of the station is a 70 metre high grounded free standing steel framework tower, which was built in 1960/61 and which carries a cage aerial for the transmitter of the ionosonde.
Over-the-horizon radar (OTH), sometimes called beyond the horizon radar (BTH), is a type of radar system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the radar horizon, which is the distance limit for ordinary radar. Several OTH radar systems were deployed starting in the 1950s and 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems. OTH radars have recently been making a comeback, as the need for accurate long-range tracking becomes less important with the ending of the Cold War, and less-expensive ground-based radars are once again being considered for roles such as maritime reconnaissance and drug enforcement.
Shortwave bands are frequency allocations for use within the shortwave radio spectrum. Radio waves in these frequency ranges can be used for very long distance (transcontinental) communication because they can reflect off layers of charged particles in the ionosphere and return to Earth beyond the horizon, a mechanism called skywave or “skip” propagation. They are allocated by the ITU for radio services such as maritime communications, international shortwave broadcasting and worldwide amateur radio. The bands are conventionally named by their wavelength in metres, for example the ‘20 meter band’. Radio propagation and possible communication distances vary depending on the time of day, the season and the level of solar activity.
The Jindalee Operational Radar Network (JORN) is an over-the-horizon radar (OHR) network that can monitor air and sea movements across 37,000 square kilometres (14,000 sq mi). It has a normal operating range of 1,000 kilometres (620 mi) to 3,000 kilometres (1,900 mi). It is used in the defence of Australia, and can also monitor maritime operations, wave heights and wind directions.
Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight conditions refer to partial obstruction by a physical object present in the innermost Fresnel zone.
Long delayed echoes (LDEs) are radio echoes which return to the sender several seconds after a radio transmission has occurred. Delays of longer than 2.7 seconds are considered LDEs. LDEs have a number of proposed scientific origins.
Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the medium distances range — usually 0–650 km. It is used for military and paramilitary communications, broadcasting, especially in the tropics, and by radio amateurs for nearby contacts circumventing line-of-sight barriers. The radio waves travel near-vertically upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 650 km from the transmitter. If the frequency is too high, refraction is insufficient to return the signal to earth and if it is too low, absorption in the ionospheric D layer may reduce the signal strength.
Amateur radio frequency allocation is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by the class of the station license.
An amateur radio propagation beacon is a radio beacon, whose purpose is the investigation of the propagation of radio signals. Most radio propagation beacons use amateur radio frequencies. They can be found on LF, MF, HF, VHF, UHF, and microwave frequencies. Microwave beacons are also used as signal sources to test and calibrate antennas and receivers.
The Jicamarca Radio Observatory (JRO) is the equatorial anchor of the Western Hemisphere chain of Incoherent Scatter Radar (ISR) observatories extending from Lima, Peru to Søndre Strømfjord, Greenland. JRO is the premier scientific facility in the world for studying the equatorial ionosphere. The observatory is about half an hour drive inland (east) from Lima and 10 km from the Central Highway. The magnetic dip angle is about 1°, and varies slightly with altitude and year. The radar can accurately determine the direction of the Earth's magnetic field (B) and can be pointed perpendicular to B at altitudes throughout the ionosphere. The study of the equatorial ionosphere is rapidly becoming a mature field due, in large part, to the contributions made by JRO in radio science.
The International Beacon Project (IBP) is a worldwide network of radio propagation beacons. It consists of 18 continuous wave (CW) beacons operating on five designated frequencies in the high frequency band. The IBP beacons provide a means of assessing the prevailing ionospheric signal propagation characteristics to both amateur and commercial high frequency radio users.
Explorer 20, also known Ionosphere Explorer-A, IE-A, S-48, TOPSI and Topside Explorer, was a NASA satellite launched as part of Explorer program. Its purpose was two-fold: long-term investigation of the ionosphere from above, and in situ investigation of ion concentrations and temperatures.