Ionosonde

An ionosonde is a special radar for the active investigation of the ionosphere. It scans from layers in the ionosphere.

Can each be explored to the maximum electron density is only half of the ionosphere. When a scan from below it is the bottom ("bottom side" ) of the ionosphere; corresponding probes are called " Bottom Side - Sounder " means. The top ( " topside " ) is usually studied from satellites of the " topside sounders " so-called.

Common models of Bottom Side - sounders are the models of the " Digisonde " series of the Center for Atmospheric Research, University of Massachusetts Lowell and the " Dynasonde " from the U.S. National Oceanic and Atmospheric Administration ( NOAA).

In Germany there is a Ionosonde in Juliusruh, which is part of a worldwide network of interconnected ionosondes, which is led by the University of Massachusetts Lowell.

Construction

An ionosonde consists of

• A short-wave transmitter which is tunable over a wide frequency range. Typically, the frequency coverage from 0.5 to 23 or 1 to 40 MHz, wherein the frequency sweeps are usually limited to about 1.6 to 12 MHz,
• A follower shortwave receiver that can track the transmitter frequency automatically
• A steep beam transmitting antenna with a suitable directional emission and efficiency over the entire frequency range used,
• May be one or more separate receiving antennae,
• Control and data analysis circuits, as well as
• Data output devices (eg screens ) to which any storage devices are connected.

The transmitter emits on the (transmitting ) antenna pulses, and the receiver receives reflected echoes from an antenna passes them to be processed by the analysis system on.

Principle

In a frequency range between 0.1 to 30 MHz, a signal transmitted from the ionosphere and is reflected back broken signal an echo signal. With increasing frequency, the transmitted signal is less sharply broken and thus penetrates more deeply into the ionosphere, before it is reflected.

From below ( bottom side ) increases by deeper penetration the reflection height of the layer from above ( topside ) it is reduced accordingly. When the critical frequency is exceeded, the ionosphere is no longer in a position to reflect the signal. Individual layers of the ionosphere have their own critical frequency, respectively.

An ionosonde sends after the sonar principle radio pulses to the ionosphere and evaluates received echoes from. The pulses are reflected dependent on the frequency of the different layers of the ionosphere from the bottom at heights of 100 to 400 km. It ranks are usually sent by pulses, so-called runs ( English "sweep "), whereby gradually the whole or a part of the corresponding short-wave frequency range is passed through. In the simplest case, only the signal propagation time is measured, from which the magnitude of the reflection can be determined. The measured height is also called virtual height.

A similar principle of operation have the beacon propagation, which are used for the evaluation of the radio weather by the ionosphere.

Applications

Ionosondes can monitor the height and the critical frequency of the ionospheric layers. About distributed receiving antennas, two-dimensional representations of totally reflected echoes developed and partially reflected echoes can also be the mesosphere are examined.

Ionosondes be used, among other things, to find the lowest operating frequency for radio transmission in the shortwave range. In conjunction with Ionosphärenheizern they serve as diagnostic tools, in conjunction with the incoherent scatter radar can be used for the calibration.

Ionogram

The results can be displayed in a Ionogrammes. Ionograms are two-dimensional graph of the signal propagation time of the reflected radio-frequency signals or the reflection calculated from it amount to the carrier frequency. For their evaluation has been around since the International Geophysical Year internationally accepted rules.

History

The basic technique was invented in 1925 by Gregory Breit and Merle Tuve and Antony in the 1920s, further developed by a number of physicists, including Edward Victor Appleton. The term " ionosphere ", and that the origin of derived terms, was proposed by Robert Watson-Watt.