The Technical Note presents the possibility of applying the classical onboard aviation radar altimeter in the function of a simple anticollision system. Currently, classical radar altimeter offers two important pieces of information for pilots: actual flight altitude and aircraft descent at the level of decision making. The goal here is to draw attention to the innovative technique of using the radar altimeter to generate further crucial information for the pilot of a helicopter or small aircraft for predicting the threat of collision with the terrain. This new technique is based on the evaluation of the Doppler frequency in the differential signal of the radar altimeter. The theoretical assumptions have been verified by simulation and experiment.Nomenclature c speed of light, m/s F D differential signal frequency of radar altimeter corresponding to Doppler effect, Hz F M frequency modulation, Hz F r differential signal frequency of radar altimeter corresponding to helicopter's altitude, Hz F rD resulting differential signal frequency shaped by radar altimeter, Hz f 0 center frequency sweep of radar altimeter, Hz H helicopter altitude, m s distance flown, m t c time remaining to the collision with terrain, s t cr critical time, s U D voltage proportional to difference of the measured frequencies at each half-period of the modulation frequency, V U H voltage proportional to altitude, V v speed of aircraft flight, m/s v v vertical component of speed, m/s α terrain inclination angle, deg β hill inclination, deg f frequency deviation, Hz
The paper focuses on the new trend of increasing the accuracy of low altitudes measurement by frequency-modulated continuous-wave (FMCW) radio altimeters. The method of increasing the altitude measurement accuracy has been realized in a form of a frequency deviation increase with the help of the carrier frequency increase. In this way, the height measurement precision has been established at the value of ±0.75 m. Modern digital processing of a differential frequency cannot increase the accuracy limitation considerably. It can be seen that further increase of the height measurement precision is possible through the method of innovatory processing of so-called height pulses. This paper thoroughly analyzes the laws of height pulse shaping from the differential frequency presented by the number that represents the information about the measured altitude for this purpose. This paper presents the results of the laboratory experimental altitude measurement with the use of a so-called double-channel method. The application of obtained results could contribute to the increase of air traffic safety, mainly in the phase of the aircraft approaching for landing and landing itself.
It is well established that strong electromagnetic fields (EMFs) can give rise to acute health effects, such as burns, which can be effectively prevented by respecting exposure guidelines and regulations. Current concerns are instead directed toward the possibility that long-term exposure to weak EMF might have detrimental health effects due to some biological mechanism, to date unknown. (1) The possible risk due to pulsed EMF at frequency 2.45 GHz and mean power density 2.8 mW/cm(2) on rat postnatal neurogenesis was studied in relation to the animal's age, duration of the exposure dose, and post-irradiation survival. (2) Proliferating cells marker, BrdU, was used to map age- and dose-related immunohistochemical changes within the rostral migratory stream (RMS) after whole-body exposure of newborn (P7) and senescent (24 months) rats. (3) Two dose-related exposure patterns were performed to clarify the cumulative effect of EMF: short-term exposure dose, 2 days irradiation (4 h/day), versus long-term exposure dose, 3 days irradiation (8 h/day), both followed by acute (24 h) and chronic (1-4 weeks) post-irradiation survival. (4) We found that the EMF induces significant age- and dose-dependent changes in proliferating cell numbers within the RMS. Our results indicate that the concerns about the possible risk of EMF generated in connection with production, transmission, distribution, and the use of electrical equipment and communication sets are justified at least with regard to early postnatal neurogenesis.
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