East Siberian Center for the Earth's Ionosphere Research (SDC ESCEIR)
Institute of Solar-Terrestial Physics SB RASUpper Atmosphere Physics and Radiowave Propagation Department
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: http://rp.iszf.irk.ru/esceir/lchmen/ionozonden.htm
Дата изменения: Sat Jun 2 09:14:57 2001 Дата индексирования: Sun Dec 23 08:47:41 2007 Кодировка: IBM-866 Поисковые слова: п п п п п п п п п п п п п п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п |
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SHAREABLE DATA CENTER
East Siberian Center for the Earth's Ionosphere Research (SDC ESCEIR)Institute of Solar-Terrestial Physics SB RASUpper Atmosphere Physics and Radiowave Propagation Department |
Composition
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Short-wave ionospheric diagnostics subdivisionChirp ionosondeChirp ionosonde main technical characteristics ааThe main instrument of our investigation is chirp ionosonde, which has the vertical (VS), oblique (OS) and back-scattering (BSS) sounding modes. Chirp ionosonde ionosphere sounding principlesLinear frequency modulated continuous signals sounding method is relatively simple and has wide application in various special-purpose systems. A typical functional diagram of the ionosonde with a continuous chirp-signal is presented in the figure :
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Let the transmitted signal have the form:
where A
0 -- signal amplitude; Then in the case of mirror reflection the signal at the receiver input has a time delay t with respect to the transmitted signal (to start heterodyne time) and has the form:
where R0 -- coefficient of signal relaxation due to the propagation and reflection process. |
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Let us assume that the heterodyne receiver chirp-signal characteristics are strictly identical to the transmitted signal characteristics. If the receiver synthesizer is started simultaneously with the transmitter synthesizer by the synchronization system, then the low frequency filter output signal has the form:
So the difference frequency W=bt is uniquely determined by the propagation time on the run. Thus the received signal heterodyning process due to the chirp-signal generator transforms difference delay information into the difference of frequency information. The received signal has a multymodal structure. Each run of propagation (propagation mode) has his own difference frequency.This peculiarity imposes some restriction on equipment, which must supply all expecting signal delays registration. The sounding chirp signal parameters must usually meet the following requirements: The working frequency range is mainly determined by the sounding mode, run of investigation and also by seasonal factors, time, and solar activity. A high frequency is usually chosen well above the expected critical frequencies, but the working range is very often restricted by sounding equipment technical characteristics and by its transmitting and receiving antennas. A typical ionosonde freuency range varies from 1 to 30 MHz. The chirp speed (b) is the parameter which mainly defined the noise stability and resolution power or sounding equipment. Chirp signals which are applying for ionosphere channel diagnostics usually have10KHz/s -- 1MHz/s. We must point out that under modulation speed increasing there is an increase in noise suppression and resolution power. |
-- initial frequency;
-- rate of frequency variation. 
,
-- difference frequency;
-- phase run.