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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Forgotten radiometeorology. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology Why forgotten? And what is this science anyway? By definition, radiometeorology is the science of the relationship of meteorological (weather) processes with the processes of radio wave propagation in the atmosphere. However, the meaning given to this definition has changed several times throughout the history of the development of radio engineering. Recall that the first radio receiver of A. S. Popov was used as a lightning detector, that is, the first practical use of radio was radio meteorological! Observation of atmospherics - radio emission pulses caused by lightning discharges, became quite widespread in the 20-30s. For example, the instrument of the Swiss physicist Lujon was known, which was called an atmoradiograph and was an improved Popov lightning detector combined with a meteorological anemokinemograph [1]. Observations were carried out at ultra-long waves (frequencies of tens of kilohertz), which have a large propagation range, so that it was possible to register remote sources of thunderstorm activity, including tropical ones. During the Second World War, when Switzerland was cut off from sources of meteorological information, thanks to observations of atmospherics, it was possible to register the occurrence of cyclones even off the coast of Florida. Crossing the Atlantic, these cyclones then determined the weather in Europe. Later, in order to more accurately locate the sources of atmospherics, the Lujon group organized in 1957-1959. observation posts in Zurich and Svalbard. Direction finding with a base of 4200 km made it possible to register thunderstorms in almost the entire northern hemisphere. Atmospheric observation techniques improved significantly when direction-finding receivers appeared with an indication of incoming pulses not by ear, but on the CRT screen. The block diagram of a modern lightning direction finder is shown in fig. 1]. This is a direct amplification receiver containing three identical channels with bandpass filters Z2-Z1 tuned to the received frequency (eg 3 kHz) and amplifiers A27-A1. Two channels receive a signal from WA3 and WA1 loop antennas crossed at right angles (magnetic ones can be used with equal success), and the third channel receives a signal from the WA2 omnidirectional whip antenna. The signal of the third channel is limited in amplitude by the limiter U3 and serves as a model for the operation of two synchronous detectors U4 and U1 installed in the first two channels.
At the outputs of synchronous detectors, the demodulated signals are proportional to the sine and cosine of the angle of arrival of the radio waves. After applying them, after appropriate amplification and formation in devices U5 and U6, to the horizontal and vertical deflection plates of the CRT, we obtain the beam deflection angle proportional to the arc tangent of the voltage ratio in the channels with loop antennas, i.e., the azimuth of the wave arrival angle. The initial alignment of the direction finder is carried out by turning the loop antennas and the U3 phase shifter in the reference signal circuit. As you can see, the direction finder is quite simple, does not contain mobile devices for rotating antennas, however, it allows you to determine the azimuth with a fairly high accuracy. Atmospheric on the screen is observed in the form of a beam ejection from the center of the screen in the direction corresponding to the azimuth, and the ejection length corresponds to the atmospheric amplitude. Thus, a polar intensity diagram of atmospherics is formed. Typhoons and hurricanes give a sharp sharp maximum on it, while the frontal regions of thunderstorms - a wide maximum in direction and less in intensity [1]. The lightning direction finding technique somehow did not receive proper coverage in the domestic literature, and in the amateur radio it is completely absent. At the same time, forecasting thunderstorms, hurricanes, squalls, showers and observing their development is extremely important, especially in rural areas. It seems that there is a wide field of activity for radio amateurs. Another aspect of radio meteorology is related to observations of the passage of radio signals in the atmosphere. In the 20s and 30s, it was taken for granted that radio reception was related to the state of the weather. There was even such a sign among radio operators: "Good weather - bad reception, bad weather - good!". At the same time, many works and studies were carried out, proving the connection between the propagation of long, medium and short waves (LW, SW and HF) with weather conditions. Radio amateurs G. I. Kazakov (Tashkent), M. A. Benashvili (Tbilisi), L. S. Leonov and A. P. Shchetinin (Moscow) took part in them. Their observations gave very valuable results, but now few people know about them. During the Great Patriotic War, there was no time for radio meteorology, but radar was developed, the ranges of decimeter, centimeter, and later millimeter waves were mastered. Then, already in the 50-60s, theoretical and experimental studies were carried out on the long-range propagation of VHF due to refraction in the troposphere, scattering on tropospheric inhomogeneities, discovered the existence of tropospheric waveguides. Radar reflections were received from clouds, precipitation zones, and even from "clear skies" - sections of the troposphere with large fluctuations in the refractive index. Thus, the "third" radio meteorology has already been formed, which studies the propagation and reflection of VHF in the troposphere [3]. It also often includes the study of the atmosphere with the help of balloons equipped with radio transmitters. Let us recall the famous radiosonde of the system of prof. Molchanov, first launched in January 1930. It was so successfully designed that even many years later it was used by most domestic weather stations. It was this radio meteorology, plus radar meteorology, that became dominant in the post-war years, completely replacing that old radio meteorology related to the Far East, SW and SW. Well-known scientists Pedersen and Austin also contributed to this “accidentally”, back in 1927-1931. who spoke in favor of the independence of the distribution of DW, SW, and HF from weather conditions (in fact, their conclusion was made as a result of observations in America of the work of European stations, and any kind of weather occurs in such open spaces [1], so there can be no dependence). Since then, provisions have been established in the science of radio wave propagation that can be found in any textbook: the propagation of DW, SW and KB is not related to the weather, the parameters of the ionosphere are determined only by processes on the Sun and the Earth's magnetic field, and the long-range propagation of radio waves in these ranges is determined by the state of the ionosphere . The influence of the troposphere is observed only on VHF and SHF. Previously, the author of these lines was also sure of this, but several cases from practice have greatly shaken this confidence. The first case occurred at a geodetic test site near Serpukhov, 100 km south of Moscow. On a summer afternoon, while listening to a Moscow radio station on long waves, I was surprised to find fluctuations in the signal level with a swing of more than 12 dB and with a frequency of several seconds! It helped that the reception was carried out on an interference level meter, in which there was no AGC, but there was a pointer indicator of the input signal level, fading on the LW when propagating over a short distance by an earth wave? It can't be! However, the arrow stubbornly walked all over the scale. In complete bewilderment, leaving the tent, I saw in the sky a huge and beautiful thundercloud approaching from the south. A comparison of the speed of the cloud with the wavelength clearly showed that the fading was caused by the interference of an ordinary ground wave and a wave reflected from the cloud. Another incident occurred on a hydrographic vessel carrying out scientific work in the straits between the Kuril Islands. Despite the remoteness from large population centers, the air was full: in the NE there were a lot of Japanese broadcasting stations, in the Far East Khabarovsk, Petropavlovsk-Kamchatsky, Vladivostok and Magadan were well heard. But one fine morning (foggy as always) the receiver in the wardroom refused to receive anything on the Far East and North and they called me to fix it. The receiver was correct. Listening to the air on a large communication receiver with the ship's radio operators showed that the signals of the mentioned radio stations were absorbed almost completely, only the carrier of the radio station of Petropavlovsk-Kamchatsky was received, rather guessed, in the telegraph mode by two points. The ether revived only at frequencies above 3,5 MHz, where a normal transmission for KB was observed. For three days in the Far East and Northeast it was "deaf as in a tank", and only gradually the passage was restored. Many years later, the author got a wonderful book [1] by Dmitry Nikolayevich Nasilov, a scientist from Moscow State University, written mainly based on the results of research in the 20s and 30s. For the first time in the literature, I read about a similar incident that occurred in a completely different region of the globe - during the voyage of the Perseus expedition ship from Arkhangelsk to Franz Josef Land (FJL). It was noted that when leaving the warm current of the Gulf Stream into the cold Arctic waters, all radio stations located to the south became barely audible or disappeared altogether. But when approaching the FJL, the audibility was restored, at the same time, hydrologists noted the appearance of another warm jet of the Gulf Stream. Observers explained the "zone of silence" by the refraction of radio waves on a powerful and extensive layer of fog over a warm current invading cold waters. Note that the situation is similar in the Kuril Islands: the warm Kuro-Sio current, coming from the Japanese islands, collides with the cold waters of the Sea of Okhotsk. The explanation of the Kuril-Kola effect was not then supported by reputable scientists, and many such facts are still not included in textbooks on radio wave propagation. But the facts are stubborn things, and experiments confirm that the phenomena of refraction, reflection and waveguide propagation are also observed on the LW, SW and HF, as well as on the VHF. In this regard, observations of the field strength of broadcasting stations are of great interest. So, for example, the American researcher R. Colwell, being 170 km from the city of Pittsburgh and measuring the field strength of the radio station of this city at a wave of 305 meters, established a 98 percent correlation with weather conditions. His own group in 1939 experimentally received reflections at HF (frequencies 1614 and 3492,5 kHz) from tropospheric layers, which are much lower than the ionospheric layer E, even at altitudes of 1 ... 2.3 km! The measured values of the reflection coefficient are about 10-4 for thin clouds in the form of haze, always present at altitudes of 12...16 km, and about 0,001...0,05 for warm front clouds, they can increase up to 0,7 (! ) for powerful cumulus and thunderclouds, often accompanied by a cold front.
Fluctuations in the field strength of radio stations during thunderstorms were noted by many - as an example, in Fig. Figure 2 shows a record of a radio station in Kiev (1209,6 meters), made by the Kiev radio receiving station in good weather (Fig. 2, a) and during a thunderstorm (Fig. 2, b) [1]. The fluctuations can be explained by the appearance of areas of increased air ionization at low altitudes. But even in the absence of thunderstorms, the approach of, for example, a warm front gives a general increase in the field strength in the LW and NE, while a cold front causes sharp fluctuations, fading, and can even lead to signal loss. Nonlinear effects are also observed in the atmosphere, which manifest themselves in the form of "overlays" on the carrier of the received radio station. M. A. Benashvili in 1938 proposed to determine the location of atmospheric fronts by the nature of the "overlays" on the signals of the LW and MW radio stations received from different directions and distances. So, a cold front in the path of radio waves generates crackles and clicks, a warm front - rustles, a solid background. In one article it is impossible to retell many of the most interesting phenomena that manifest themselves when carefully listening to the ether and studying the processes of radio wave propagation. The purpose of this publication is to draw the attention of radio amateurs to these half-forgotten phenomena, somehow lost in our age of computers and satellite communications. It is not superfluous to recall that even cosmic radio emission was discovered by ordinary radio engineers who performed everyday work on measuring radio interference, and long-range propagation of HF was discovered by radio amateurs. Literature
Author: V.Polyakov, Moscow
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