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A SEMI-AUTOMATIC INTERPRETATION OF IONOGRAMS

B.O. Vugmeister and V.V. Radionov

Institute of Solar-Terrestrial Physics

664033 Irkutsk, Russia

Advances in ionospheric sounding techniques that made possible a variety of digital ionosonde designs and have helped researchers anticipate the possibility of a fully automated process of ionogram analysis and interpretation.

So far, however, these authors are unaware of any processing system capable of accurately scaling the 16 ionospheric characteristics endorsed by URSI. The main problems arising in ionogram analysis may be reduced to three:

- signal detection

- ray tracing

- ionogram interpretation

Usually, the first and second problems are resolved by choosing an appropriate value of ionosonde potential (high sensitivity of the receiver, adequate power of the transmitter, the use of a coded signal). Besides, such problems are tackled in related areas of knowledge (radar, nuclear physics, etc.).

Ionogram interpretation is accomplished following reasonably formalised rules (1); however, as our investigations and results [2,3] reported by other authors show:

a) a correct determination of ionospheric parameters is possible in no more than 80 percent of cases,

b) some parameters (type Es, for example) have not yet been automatically determined at all.

Obviously, large-scale computer treatment of ionograms would be followed by the transfer of the data to the WDC for storage. But no data would be preferable to storing incorrect data.

The above reasoning has led us to the idea that it would be premature to exclude man from the ionogram interpretation process. Based on this, it was possible to formulate a request for proposal (RFP) involving the development of a system for handling ionograms interactive.

The system's program software is implemented in FORTRAN and Macroassembler for micro-computers DVK-3M (PDP).

The system is designed to solve the following problems:

signal processing to increase the signal/noise ratio

ionogram interpretation in the interactive mode

automatic transmission of an ionogram via telex.

The signal is processed through an post-detector accumulator with frequency averaging. The noise level is determined for every sounding frequency (normally in 5 kHz steps). For this purpose, the signal is analysed for those height ranges where an ionospheric reflection is obviously absent. A mean noise level is determined for the entire frequency range in which the signal amplitude (normally 5x5 kHz) is calculated. The value of the mean noise level is used as the threshold when making a decision about the presence or absence of the signal.

In the interactive mode of ionogram interpretation, the height-frequency characteristic obtained by the above method, is displayed on the computer terminal, simultaneously with operator prompting (a list of allowable instructions that varies depending on operating conditions - according to the interpretation of the Es-layer or the E-, F1- and F2-layers) and with values of parameters to be determined. By moving the cursor along the ionogram, the operator detects the desired point and, by depressing an appropriate key, enters the name of the measured parameters and (if necessary) its signatures. In the process of interpretation, the operator is able to change the cursor step, erase incorrectly marked values of parameters and erase the data frame of a given size.

The points marked on the ionogram by the operator are displayed and maintained until the ionogram interpretation is terminated.

Data obtained are used to generate a series of (usually hourly) values of ionospheric parameters and a file-telegram in the IONKA BE code used by the Russian Agency on Hydrometeorology and Environmental Control.

The subsystem for data transmission via telex consists of the telegraphic line interface and the program software. The subsystem operates in active and passive (data transmission on request) modes. In the active mode, the subsystem performs the following functions:

calling a telegraph office

dialling the wanted party

checking the answer-back of the wanted party

transmitting the file-telegram

handling and recording of the acknowledgment of data received.

The data transmission subsystem receives, handles and communicates to the operator the service information of the telegraph office.

The system for interactive processing of ionograms permits ionogram interpretation in real time (average processing time - 90 seconds) and the transmission of data obtained via telex.

References

1. Piggott W. R. and K. Rawer, URSI Handbook of Ionogram Interpretation and Reduction. Report UAG-23A, World Data Center A for Solar and terrestrial Physics, 1978.

2. Reinisch Bodo W. and Xuegin Huang. Automatic Calculation of Electron Density Profiles from Digital Ionograms. 3. Processing of Bottomside Ionograms. Radio Sci., 1983, v. 18, No. 3.

3. Galkin I.A. The Program Software for Automatic Processing of Vertical-Incidence Sounding Ionograms. II. Interpretation of the Height-Frequency Characteristic. Preprint No. 22-88, SibIZMIR, Irkutsk, 1988.

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