ultra short pulse radiolocation
coefficient linear attenuation
B.Ch. Dorzhiev, O.N. Ochirov, A.V. Bazarov
At present report, results of a ground radar-location of wood environments by a nano-second radar with carrying frequency 10 GHz and duration of a pulse 10 ns are submitted. The following tasks were put out at realization of researches: an experimental rating of ultra-short pulse radar-location of wood environments, a rating of attenuation properties wood environment of various (deciduous and coniferous) types, a rating of an opportunity of construction of the radio tomography image of a wood site by a method of angular multi foreshortening scanning. In introduction the definitions ultra wide band and of ultra-short pulse signals and their specific features are briefly considered. Two properties of ultra-short pulse signals, namely - high resolution on range and effect of reflections contrast from objects are marked. The specified properties are caused by three factors: a small pulse volume, absence of lateral petals on an axis of range at correlation function of rectangular sounding signal, reduction of an echo - signal from a surface and passive interference. Radar location are carried out on the basis of measuring complex, including a nano-second radar, parabolic antenna with the rotary device, digital oscillograph TDS1012 with the block of expansion TDS2CMA, notebook, and electro generator on 220 V. The basic characteristics of radar transmitter and receiver are also given.
The rating of signal attenuation by a deciduous wood is carried out by a method of relative measurements with use of a corner reflector (CR) when the last are deep into wood on fixed range. The attenuation coefficient was defined by comparison of signals from CR on first (wood edge) and subsequent positions. Absolute values of the reflected signals were defined from volt-watt characteristic of the radar receiver. The average value of attenuation coefficient for a deciduous wood is 0.29 dB/m. The other method is used at location of a coniferous wood. It is applied the method of angular scanning. The recording signal represents the diagram of dependence of the reflected signal amplitude from time of its arrival to registration system. The level of the reflected signal turns out as a result of summation of signals from trunks and crown of trees. Decrease of an analytical signal approximated by linear dependence. The average value of attenuation coefficient determined on the given dependences is 0.2 dB/m. In case of ground measurements the basic contribution is brought in by reflections from trunks, therefore is put a task to maximum reduce influence of trees crowns. The method of the spectral analysis is used for decomposition of an analytical signal on harmonics. After exception of high-frequency harmonics appropriate to the contributions from branches and needles, the restored signal by a method of return transformation Fourier is received. The received signal contains more expressed maxima appropriate to reflections from trunks of trees. Thus the character oscillogram of a restored signal is closer to exponent dependence.
The power spectrum of a signal assumes its description by the certain law of distribution of probability similarly as are described fluctuations of electromagnetic radiation intensity. The approximation of a power spectrum by the lognormal law of distribution seems to satisfactoriness. However, for this purpose, it is necessary to receive the basic numerical characteristics, with which help it is possible to carry out a comparative rating of areas of existence specified, and it is possible also of other distributions, in particular, exponential law of distribution or Nakagami distribution. It will allow to establish deeper connections between temporary and frequency areas of a signal. By analogy of concept, it is possible to name "a radar portrait" of object spectral performance of an analytical signal for wood environment as "a spectral portrait" woods.
At tomography of a wood in a case of narrow directional antenna, the method of angular scanning is optimum. The set of projections is formed as summation of registered oscillograms at each corner of scanning. For each angle data regulation is carried out in view of average value of linear attenuation coefficient. The tomogram of a test site is submitted as grey gradation mode, where brighter areas concern to areas with higher values of the reflected signal and correspond to site either separate tree, or group of the close located trees. The tomogram matching with the plan of a wood site shows the satisfactory consent.
In summary, the following conclusions are made. The considered features of ultra-short pulse location - high resolution on an example CR, taking place inside wood environment, and effect of contrast of reflections from separate trees are experimentally confirmed. The received experimental ratings of factor of attenuation coefficient allow to expand its spectral dependence. The further development of tomogram construction method of wood tested sites will allow to solve a task of restoration of a wood, including such basic parameters, as a tree stock and biomass.