Ionoprobe

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The antenna system of the HAARP ion probe
Example of an ion probe system displaying an ionogram

An ion probe is a special type of radar for the active investigation of the ionosphere . It scans layers in the ionosphere.

Only half of the ionosphere can be probed to the maximum electron density at a time. When scanning from below, it is the “bottomside” of the ionosphere; Corresponding probes are referred to as "bottom-side sounders". The upper side ("topside") is mostly examined from satellites by the so-called "topside sounders".

Common models of bottom-side sounders are the models of the “Digisonde” series from the Center for Atmospheric Research at the University of Massachusetts Lowell and the “Dynasonde” from the US National Oceanic and Atmospheric Administration (NOAA).

In Germany there is an ion probe in Juliusruh , which is part of a worldwide network of interconnected ion probes, which is managed by the University of Massachusetts Lowell.

In the Falkland Islands, there is an ion probe at Port Stanley .

construction

An ion probe consists of

  • a shortwave transmitter that can be tuned over a wide frequency range. Typically, the frequency coverage is 0.5 to 23 or 1 to 40 MHz, with frequency sweeps usually limited to around 1.6 to 12 MHz,
  • a traveling shortwave receiver that can automatically track the transmission frequency,
  • a steep beam transmitting antenna with suitable, directional radiation characteristics and efficiency over the entire frequency range used,
  • possibly one or more separate receiving antennas,
  • Control and data analysis circuits, as well as
  • Data output devices (e.g. monitors) to which storage devices may be connected.

The transmitter sends pulses via the (transmitting) antenna, the receiver receives reflected echoes via an antenna and forwards them to the analysis system for processing.

principle

In a frequency range between 0.1 and 30 MHz, a signal sent against the ionosphere is broken back and an echo signal is reflected. With increasing frequency, the transmitted signal is broken back less strongly and thus penetrates deeper into the ionosphere before it is reflected.

From below (bottomside) the deeper penetration increases the reflection height of the layer, from above (topside) it decreases accordingly. When the critical frequency is exceeded, the ionosphere is no longer able to reflect the signal. Individual layers of the ionosphere each have their own critical frequency.

An ion probe sends radio pulses to the ionosphere according to the echo sounder principle and evaluates received echoes. The pulses are reflected on different layers of the ionosphere, depending on the frequency, from below at heights of 100 to 400 kilometers. Usually series of pulses are sent, so-called sweeps, whereby the whole or part of the corresponding shortwave frequency range is passed through step by step. In the simplest case, only the signal transit time is measured, from which the level of reflection can be determined. The measured height is also called the virtual height.

The propagation beacons , which are used to assess radio weather through the ionosphere, have a similar functional principle .

Applications

Ion probes can thus monitor the height and the critical frequency of the ionospheric layers. Two-dimensional representations of totally reflected echoes can be developed using distributed receiving antennas and the mesosphere can also be examined using partially reflected echoes.

Ion probes are used, among other things, to find the most favorable operating frequency for radio transmissions in the shortwave range. In connection with ionospheric heaters , they serve as diagnostic instruments, in connection with incoherent scatter radars they can be used for their calibration.

Ionogram

Typical ionogram with foF2 of approximately 5.4 MHz.

The results can be displayed in the form of an ionogram. Ionograms are two-dimensional graphs of the signal propagation time of the reflected high-frequency signals or the calculated reflection height above the carrier frequency. For their evaluation there have been internationally accepted rules since the International Geophysical Year .

history

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

Web links

Commons : Ionoprobe  - collection of images, videos and audio files

literature

  • Davies, Kenneth: Ionospheric Radio  (= IEE Electromagnetic Waves Series # 31). Peter Peregrinus Ltd / The Institution of Electrical Engineers, London, UK 1990, ISBN 0-86341-186-X , pp. 93-111.
  • Gwyn Williams, G4FKH: Interpreting Digital Ionograms . In: RSGB (Ed.): RadCom . 85, No. 05, May 2009, pp. 44-46.
  • Breit, G. and Tuve, MA: A Test of the Existence of the Conducting Layer . In: Physical Review . 28, No. 3, 1926, pp. 554-575. bibcode : 1926PhRv ... 28..554B . doi : 10.1103 / PhysRev.28.554 .
  • Appleton, EV: The Timing of Wireless Echoes, the use of television and picture transmission . In: Wireless World . No. 14, January 1931, pp. 43-44.

swell

  1. ↑ a b M. T. Rietveld, JW Wright, N. Zabotin, MLV Pitteway: The Tromsø dynasonde . In: Polar Science . tape 2 , no. 1 , March 2008, p. 55–71 , doi : 10.1016 / j.polar.2008.02.001 (English).
  2. ↑ UMass Lowell Center for Atmospheric Research: Ionoponde Station Map
  3. ^ Background to Ionospheric Sounding
  4. Jump up ↑ KJF Sedgemore, PJS Williams, GOL Jones, JW Wright: A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere . In: European Geosciences Union (Ed.): Annales Geophysicae . tape 14 , no. 12 . Springer-Verlag, 1996, p. 1403-1412 , doi : 10.1007 / s00585-996-1403-x (English, ann-geophys.net [PDF]).
  5. ↑ WR Piggott, K. Rawer (Ed.): URSI Handbook on Ionogram Interpretation and Reduction. Elsevier Publ.Comp., Amsterdam 1961 (translations exist in Chinese, French, Japanese and Russian).
  6. ↑ FC Judd, G2BCX: Radio Wave Propagation (HF bands) . Heinemann, London 1987, ISBN 0-434-90926-2 , pp. 12-20, 27-37.