ЭКОЛОГИЧЕСКИЕ АСПЕКТЫ ИСПОЛЬЗОВАНИЯ АЛЬТЕРНАТИВНОЙ ЭНЕРГЕТИКИ, ЭКОЛОГИЯ МЕГАПОЛИСОВ, МАЛЫХ ГОРОДОВ, ДЕРЕВЕНЬ
ECOLOGICAL ASPECTS OF ALTERNATIVE ENERGY AND ECOLOGY OF MEGAPOLISES, CITIES AND VILLAGES
ALGORITHMIC SYSTEM FOR IDENTIFYING BIRD RADIO-ECHO | AND PLOTTING RADAR ORNITHOLOGICAL CHARTS i
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L. Dinevich, Y. Leshem |
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George S. Wise Faculty of Natural Sciences, Dept. of Zoology |
Tel-Aviv University, 69978, Israel J
E-mail: dinevich@barak-online.net; leonid@post.tau.ac.il g
The proposed algorithmic system for identifying bird radio-echo against the background of reflectors of other types was developed within a novel approach based on the analysis of echo movement characteristics. A long-term implementation of the previously designed algorithm (Dinevich et al. 2004) has demonstrated its ability for identifying bird echo with high confidence. At the same time, this work enabled to determine the directions of further research, aimed at: a) significant reduction of computation time; b) increasing echo identification accuracy in cases of weak echo and of large dense bird masses; c) plotting radar ornithological charts on-line.
In the course of the present study, a comparative analysis was carried out of radio-echo typical of different categories of reflectors. As a result, a set of characteristics was obtained that distinctly specify bird echo and distinguish it from echoes of other types of reflectors. The algorithmic system based on this set of characteristics enables to determine whether a radio-echo movement belongs to one of the four patterns: a) straightforward at non-uniform velocity; b) straightforward at uniform velocity; c) significant deviation from a straight line, non-uniform velocity and d) chaotic undirected shifts. The data on echo movement pattern were used for plotting bird (bird group) flight vectors. In order to filter off false vectors, a special algorithmic procedure was devised based on a number of additional echo characteristics, including the threshold value, the extent of chaotic status in the direction of closely located vectors, the maximum and minimum velocities etc. Another proposed algorithmic procedure enables to make a prompt and accurate (at least 80% confidence) decision on the "bird-not bird" origin a particular echo on the basis of its fluctuation pattern. The system enables online plotting of operational ornithological charts every 12-15 min, including charts that combine meteorological and bird monitoring data, and thus is as an efficient means of maintaining air traffic safety in complicated meteorological and ornithological conditions. In view of the fact that MRL-5 radars are located in many countries and cover an extremely vast territory, it appears expedient to connect them into a network. Using the algorithmic system for bird echo identification by means of MRL-5 radar, such a network could perform intercontinental bird monitoring in the real-time mode, contributing to providing collective air traffic safety.
1. The Objectives of the Study
The present study has been carried out within the novel approach to bird echo identification based on an algorithmic analysis of specific parameters characterizing echo movement. It was shown in the previous work (Dinevich et al., 2004) that during bird migration, the coordinates of bird echo centers form almost straight lines over flight legs. This property was used as the basis of the identification algorithm. A long-term implementation of the algorithm has demonstrated not only the advantages of the method, but also the directions of its further improvement. In some cases, the previously developed techniques proved inapplicable, e.g. when echo from small birds were of power below
the noise level and, therefore, were not registered
in some of the scans within the scan cycle pre- i
scribed by the algorithm. In these cases, straight t
line segments that should have served as the basis |
for echo identification were disrupted. Another ^
problem arose when the mass of birds was espe- §
a
cially dense and rapidly moving, which sometimes |
resulted in the system's mistakenly taking sum- I
mated bird echoes for reflections from ground clut- p
ter, thus excluding those echoes from the further i
analysis. Yet another problem to be solved was g
reducing the computation time. 0
The objective of the present study was to reveal additional parameters that are distinctively characteristic of bird echo and use them to develop a more accurate and prompt algorithmic system
Статья поступила в редакцию 13.09.2005. The article has entered in publishing office 13.09.2005.
for echo identification. As in the previous study, the data was obtained by means of MRL-5 radar.
MRL-5, which is a high-grade meteorological radar designed mainly for cloud monitoring, has a capability of full azimuth scanning (0°-360°), the elevation range of minus 2° to +90° in the upper <t hemisphere and a symmetric narrow beam operat-^ ing simultaneously at two wave-lengths (3.2 cm and
5 10 cm). The application of MRL-5 radar for bird u monitoring and the system of primary data pro-| cessing are described in a number of studies (AbI shayev et al., 1980; Abshayev et al., 1984; Dinev-^ ich et al., 2000; Dinevich et al., 2004).
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£ 2. The basic principles of bird echo identification underlying the proposed algorithm
Comparative analysis of echoes reflected from different categories of objects shows that there are sets of distinctive properties typical only of a particular category.
Ground clutter echoes are characterized by considerable extension in space, high signal power, wide spectra of fluctuation, amplitude and frequency, as well as by relative immobility (Atlas, 1967; Hajovsky et al., 1966; Chernikov, 1979; Dinevich et el., 2001).
Considerable extension in space is also typical of echoes from clouds of different types, including convective and stratus clouds, that tend to shift in the direction of dominating wind flow. In contrast to bird echo, the echo of atomized clouds and precipitation is larger at 3 mm wavelength than that at 10 cm, while its polarization signal characteristics are typical of spherical targets. The value of differential reflexibility which is the ratio of horizontally reflected echo (at horizontally polarized illumination) to vertically reflected echo (at vertically polarized illumination) is close to unit1 for small drops. Echoes from large-drop clouds at 3cm and 10 cm wavelengths are considerably more powerful than bird echoes (Atlas, 1967; Shupiatzky, 1959; Chernikov, 1979; Doviak and Zrnic, 1993; Dinevich et al., 1994; Zrnic and Ryzhkov, 1998).
It is typical of echoes from visually unobserv-able atmospheric inhomogeneities to have low power, chaotic direction pattern while moving in space <t and polarization parameters that are close to those ¡S of spherical hydrometeors (Shupiatzky, 1959; Bat-^ tan, 1963, 1973; Lofgren and Battan, 1969; Doviak I and Zrnic, 1993; Zrnic and Ryzhkov, 1998; Ven-1 ema et al., 2000).
| Aircraft echoes are characterized by high pow-
| er and velocities (Daniel et al., 1999; Skolnik, ° 1970). Insects reflect low-power echoes whose di-
6 rection and velocity usually coincides with those g of the wind (Hajovsky et al., 1966; Glover and 8 Hardy, 1966; Skolnik, 1970).
Finally, bird echoes are of relatively low power (Z < 30 dBZ), their movement being forward and relatively straightforward. The maximum amplitude fluctuations occur in the low frequency band (below 10 dB within 2-50Hz band). Bird echoes at 10 cm wavelengths are more powerful than those at 3 cm wavelength, their polarization character-
istics being typical of horizontally oriented targets and differential reflexibility considerably exceeding unit (Lack D., 1959; Houghton, 1964; Eastwood, 1967; Chernikov and Schupjatzky, 1967; Chernikov, 1979; Bruderer, 1969, 1997A, 1997B; Bruderer B., 1992; Ganja I., Zubkov M., Kotjazi M., 1991; Russell and Gauthreaux, 1998; Gauthreaux et al., 1998; Miller et al., 1998; Buurma, 1999; Larkin et al., 2002; Gudmundsson et al., 2002; Komenda-Zehnder et al., 2002; Gauthreaux, Bels-er, 2003; Larkin et al., 2002).
In order to obtain data on specific properties of bird echo, we analyzed echo fields obtained by photographing the radar screen with an open objective, within horizontal scans performed at constant vertical angle, both during one scan (Fig. 1a) and during 18 scans (3 min; Fig. 1b).
Fig. 1c shows the same echo field after the digital data processing and data summation over 18 scans.
Comparative analysis of the three figures shows that the main common characteristic of bird echo is its specific movement, resulting in transformation of dotty radio-echo (Fig. 1, a) into streaks (Fig. 1, b). The streaks are relatively straightforward (Fig. 1, b, c). The increments in the length of the streaks take place as the result of the echoes' forward movement from scan to scan. At the same time, the number of echo dots forming most streaks is smaller than the number of scans, hence the straightforwardness of streaks is disrupted by a change of direction. To sum up, bird echoes do move, and this movement has pronounced distinguishing characteristics.
The goal of the present study was:
a) to reveal those characteristics, related to: uniformity of direction and velocity; changes in movement linearity; specificity of echo fluctuation etc.;
b) to analyze the revealed characteristics as a system of parameters and to use these parameters as the basis for an algorithmic system for prompt and accurate bird echo identification.
The first step of the procedure was aimed at identifying moving echoes and setting up the conditions for collecting the relevant data.
3. Primary radio-echo identification on the basis of echo movement
The primary source of data relevant for the task of bird echo identification is radio-echo fields obtained by summation of data collected over a prescribed number of c
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