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THE ROUTINE DIAGNOSIS OF THE IONOSPHERE FOR THE SHORT-TERM FORECAST OF HF AND VHF PROPAGATION
R. G. Minullin, O. N. Sherstyukov, V. I. Nazarenko,SA. L. Sapaev, A. D. Akchyurin
Physics Faculty, Kazan University, RUSSIA
The routine diagnosis of ionospheric conditions can be accomplished by real-time measurements made within regional ionospheric networks. A proposed network design consists of seven digital ionosondes, one of which is at the centre of a region, the others being distributed around the periphery of the region. The ionosondes must be synchronised to operate alternatively in vertical and oblique mode.
The operating cycle of such a regional network starts with the operation of the central ionosonde in vertical sounding mode. At this time, the vertical sounding (VS) is also recorded at all peripheral stations. The same aerials may be used for VS and oblique incidence (OS) operation. Our experiments have shown that delta aerials, intended for vertical sounding, receive ionograms when oblique sounding at a distance of 1800 km. This was tested over the paths Moscow-Kazan (700 km) and Kaliningrad-Kazan (1800 km). Receiving oblique ionograms provides information about ionospheric conditions at the mid-point between the central and peripheral station.
In the next time interval, a vertical sounding is carried out by each peripheral stations in turn. The nearest neighbouring peripheral ionosonde, arranged in a large circle of radius 1400-1600 km, receive radiation from each peripheral ionosonde after reflecting from the ionospheric layers. Thus, OS ionograms are recorded in addition to each VS which characterise ionospheric conditions for points between peripheral stations at a distance of 700-800 km. Taking into account the correlation properties of the regular ionospheric layers (high within 700-900 km), the area of control may be equal to a circle with a diameter of approximately 5000 km.
Sounding data are processed at peripheral stations to reduce their content from 100 kBytes to 1kByte. If necessary, a further reduction by an order of magnitude can occur. After reduction, the results of the sounding are transmitted to the central station.
The main computer at the central site periodically calculates the present state of the ionosphere over the region, which is promptly corrected by data from the peripheral stations. On the basis of the corrected model, the forecast state of the ionosphere is determined. Consumers of ionospheric information entering into contact with the central station have information about the present as well as the forecast state of the ionosphere. An independent, autonomous communication link not subjected to ionospheric influence is then required.
The transmitters and receivers at the ionospheric stations may also be used for transmitting ionospheric information. After the transmission of the information, the transmitters and receivers then return to their usual function. Thus the sounding and transmission of information will alternate periodically in time.
Meteor burst communications  could be an alternative method for transmitting ionospheric information. Meteor communication is possible in the range 25-60 MHz over distances up to 1800 km and is a system of intermittent communication, where the duration of contact may be from part of a second to a few seconds with pauses which may run to tens of seconds. However, thanks to the wide bandwidth of a meteor radio channel (2 MHz or more) the rate of information transfer can be large during contact [2,3].
Daytime meteor radio communications have unfavourable conditions at 1800 LT. At this time, the number of meteor reflections is least with season, the minimum in meteor numbers occurs in spring. Calculations for these worst conditions show that an ordinary ionogram of 1 kB may be transmitted via the meteor channel in individual contacts of a few tenths of a second.
Meteor communication is not subjected to ionospheric influence or a rise in radiowave absorption, because radio communication is carried out mainly in the meter wavelength range. Signals reflected from meteor trails may be received in a bounded zone of a few tenths of a km radius about a receiving station. Because reception outside the zone is not possible, peripheral stations may work at one carrier frequency without interfering with each other. At the central collection point of ionospheric information, special steps need not be taken to time-separate the stations because of the random nature of contact with the peripheral stations. Meteor communication selects the time and duration of a session of information transmission automatically.
For oblique sounding, the peripheral and central stations must be synchronised and locked to a common scale of time. Currently, synchronisers are locked via the transmission of exact time signals from radio stations in the decameter radiowave range. Such frequencies are subject to ionospheric influences, particularly in high latitudes, which may result in a complete loss of radio communication. Meteor communication makes it possible to solve this problem. Thanks to the broad band of transmission, exploratory experiments have shown that the meteor channel may provide a locked scale of time with errors of no more than tens of nanosecond. This is higher than the precision required for synchronising ionosondes, which need to be mutually locked within tens of microseconds. Thus, high precision timing within the given region may be provided by an ionospheric network which has a meteor communication system. Exact timing requires checking and correcting at intervals from tens of hours to a few days so that the communication channel access for this objective is low. Therefore, this channel may also be provided by the meteor communication system intended for ionogram transmission to the central station.
Central stations of regional networks may be mutually connected at key border points. As a result, regional centres may exchange data about the current ionospheric situation and maintain a routine ionospheric map for a large region of the Earth.
Thus, such a variant of the regional ionospheric network when based on meteor communication channels between central and peripheral stations, solves the problem of obtaining routine ionospheric information for the control and reliable short-term forecasting of HF and VHF propagation conditions.
A regional ionospheric network may allow the prompt recognition of the presence and movement of sporadic E-layers, as well as ionospheric disturbances and the ionospheric response to "heating" and surface and nuclear explosions etc. All this timely information may be immediately transmitted to the appropriate consumers. A network with such meteor channels of communication may also be used for the receipt and transmission of meteorological and geophysical information to consumers spread over a large geographic region, along with other low data rate information.
Minullin, R. G. The Variants of Regional Ionospheric Networks, Ionosfernye issledovania. Moscow, 1994. N50 (in the press).
Kazantsev, A. N. Meteor Radio Communication on Ultra-short Waves. Moscow. F.L., 1961. 286p.
Minullin, R. G., Palii, G. H., Sidorov, V.V. and another. Locking Scales of Time to a State Standard by Using Meteor Reflections. Izmeritelnaya tekhnika. 1971. N1. P.22.
Boikov, V. I., Zhulina, E. M., Minullin, R.G. and another. Influence of Proton Flares on Radiowave Propagation in the Subaurora Region. Geomagnetizm in Aeronomia. 1973 V.13, N6. P.1116.
Zhulina, E. M., Kurganov, R. A., Minullin, R. G. and another. Influence of Auroral Absorption on the Numbers of Meteor Reflections. Geomagnetizm in Aeronomia. 1978. V.18. N4. P.734.