1、 Recommendation ITU-R P.833-9 (09/2016) Attenuation in vegetation P Series Radiowave propagation ii Rec. ITU-R P.833-9 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication servi
2、ces, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication
3、Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by p
4、atent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/
5、publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation
6、RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V
7、 Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2016 ITU 2016 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permi
8、ssion of ITU. Rec. ITU-R P.833-9 1 RECOMMENDATION ITU-R P.833-9 Attenuation in vegetation (Question ITU-R 202/3) (1992-1994-1999-2001-2003-2005-2007-2012-2013-2016) Scope This Recommendation presents several models to enable the reader to evaluate the effect of vegetation on radiowave signals. Model
9、s are presented that are applicable to a variety of vegetation types for various path geometries suitable for calculating the attenuation of signals passing through vegetation. The Recommendation also contains measured data of vegetation fade dynamics and delay spread characteristics. Keywords Veget
10、ation, attenuation, fade dynamics, delay spread, terrestrial systems, Earth-space systems The ITU Radiocommunication Assembly, considering that attenuation in vegetation can be important in several practical applications, recommends that the content of Annex 1 be used for evaluating attenuation thro
11、ugh vegetation with various models addressing a frequency range from 30 MHz to 100 GHz. Annex 1 1 Introduction Attenuation in vegetation can be important in some circumstances, for both terrestrial and Earth-space systems. However, the wide range of conditions and types of foliage makes it difficult
12、 to develop a generalized prediction procedure. There is also a lack of suitably collated experimental data. The models described in the following sections apply to particular frequency ranges and for different types of path geometry. 2 Obstruction by woodland 2.1 Terrestrial path with one terminal
13、in woodland For a terrestrial radio path where one terminal is located within woodland or similar extensive vegetation, the additional loss due to vegetation can be characterized on the basis of two parameters: the specific attenuation rate (dB/m) due primarily to scattering of energy out of the rad
14、io path, as would be measured over a very short path; 2 Rec. ITU-R P.833-9 the maximum total additional attenuation due to vegetation in a radio path (dB) as limited by the effect of other mechanisms including surface-wave propagation over the top of the vegetation medium and forward scatter within
15、it. In Fig. 1, the transmitter is outside the woodland and the receiver is a certain distance, d, within it. The excess attenuation, Aev, due to the presence of the vegetation is given by: Aev = Am 1 exp ( d / Am) (1) where: d : length of path within woodland (m) : specific attenuation for very shor
16、t vegetative paths (dB/m) Am : maximum attenuation for one terminal within a specific type and depth of vegetation (dB). FIGURE 1 Representative radio path in woodland It is important to note that excess attenuation, Aev, is defined as excess to all other mechanisms, not just free space loss. Thus i
17、f the radio path geometry in Fig. 1 were such that full Fresnel clearance from the terrain did not exist, then Aev would be the attenuation in excess of both free-space and diffraction loss. Similarly, if the frequency were high enough to make gaseous absorption significant, Aev would be in excess o
18、f gaseous absorption. It may also be noted that Am is equivalent to the clutter loss often quoted for a terminal obstructed by some form of ground cover or clutter. The value of specific attenuation due to vegetation, dB/m, depends on the species and density of the vegetation. Approximate values are
19、 given in Fig. 2 as a function of frequency. dAmgD i s t a nc e i n w ood l a nd, dExcessloss(dB)AevTx RxRec. ITU-R P.833-9 3 Figure 2 shows typical values for specific attenuation derived from various measurements over the frequency range 30 MHz to about 30 GHz in woodland. Below about 1 GHz there
20、is a tendency for vertically polarized signals to experience higher attenuation than horizontally, this being thought due to scattering from tree-trunks. FIGURE 2 Specific attenuation due to woodland It is stressed that attenuation due to vegetation varies widely due to the irregular nature of the m
21、edium and the wide range of species, densities, and water content obtained in practice. The values shown in Fig. 2 should be viewed as only typical. At frequencies of the order of 1 GHz the specific attenuation through trees in leaf appears to be about 20% greater (dB/m) than for leafless trees. The
22、re can also be variations of attenuation due to the movement of foliage, such as due to wind. The maximum attenuation, Am, as limited by scattering from the surface wave, depends on the species and density of the vegetation, plus the antenna pattern of the terminal within the vegetation and the vert
23、ical distance between the antenna and the top of the vegetation. Measurements in the frequency range 105-2 200 MHz carried out in mixed coniferous-deciduous vegetation (mixed forest) near St. Petersburg (Russia) on paths varying in length from a few hundred meters to 7 km with various species of tre
24、es of mean height 16 m. These were found to agree on average with equation (1) with constants for specific and maximum attenuation as given in Table 1. VH103102101011100 M H z10 M H z 10 G H z1 G H z 100 G H zV : ve r t i c a l pol a r i z a t i onH : hor i z ont a l pol a r i z a t i onSpecificatte
25、nuation(dB/m)F r e que nc y4 Rec. ITU-R P.833-9 TABLE 1 Parameter Frequency (MHz) and polarization Frequency, MHz 105.9 Horizontal 466.475 Slant 949.0 Slant 1852.2 Slant 2117.5 Slant (dB/m) 0.04 0.12 0.17 0.30 0.34 m (dB) 9.4 18.0 26.5 29.0 34.1 A frequency dependence of Am (dB) of the form: fAAm 1
26、(2) where f is the frequency (MHz) has been derived from various experiments: Measurements in the frequency range 900-1 800 MHz carried out in a park with tropical trees in Rio de Janeiro (Brazil) with a mean tree height of 15 m have yielded A1 = 0.18 dB and = 0.752. The receiving antenna height was
27、 2.4 m. Measurements in the frequency range 900-2 200 MHz carried out in a forest near Mulhouse (France) on paths varying in length from a few hundred metres to 6 km with various species of trees of mean height 15 m have yielded A1 = 1.15 dB and = 0.43. The receiving antenna in woodland was a /4 mon
28、opole mounted on a vehicle at a height of 1.6 m and the transmitting antenna was a /2 dipole at a height of 25 m. The standard deviation of the measurements was 8.7 dB. Seasonal variations of 2 dB at 900 MHz and 8.5 dB at 2 200 MHz were observed. Measurements in the frequency range 105.9-2 117.5 MHz
29、 carried out in two forest-park areas with coniferous-deciduous vegetation (mixed forest) in St. Petersburg (Russia) with a tree height of 12 to 16 m and average distance between them was approximately 2 to 3 m, that corresponds to the density of 20-10 tree/100 m2 have yielded A1 = 1.37 dB and = 0.4
30、2. To receive the signal, a quarter-wave length dipole antenna at 1.5 m above the ground level was used. The distance between the receiver and the transmitter antenna was 0.4 to 7 km, and paths for measurement were chosen so as to have line-of-sight between these antennas without any obstacles but o
31、nly the woodland to be measured. Different phases of the experiment were performed in similar weather conditions: dry weather, wind speed 0 to 7 m/s. Measurements made in southern England to a depth of 200 m through mixed coniferous-deciduous woodland gave a value for Am of 46 dB at a frequency of 3
32、 605 MHz. The measurements were made with directional antennas at 2 m and 10 m above ground. Multipath effects were averaged over hundreds of individual measurements made over five paths. Measurements were carried out in summer and winter, but no significant seasonal variation was seen. 2.2 Satellit
33、e slant paths Representative radio path in woodland: In Fig. 3, Transmitter (TX) and Receiver (RX) are outside the woodland. The relevant parameters are: vegetation path length, d; average tree height, hv; height of the Rx antenna over ground, ha; Rec. ITU-R P.833-9 5 radio path elevation, ; distanc
34、e of the antenna to the roadside woodland, dw. FIGURE 3 Representative radio path in woodland with vegetation path length, d, average tree height, hv, height of the Rx antenna over ground, ha, radio path elevation, , and distance of the antenna to the roadside woodland, dw To describe the attenuatio
35、n loss, L along both, horizontal and slant foliage path propagation, the following model is proposed: L(dB) = A f B d C ( + E)G (3) where: f: frequency (MHz) d: vegetation depth (m) : elevation (degrees) A, B, C, E, and G: empirical found parameters. A fit to measurements made in pine woodland in Au
36、stria gave: L(dB) = 0.25 f 0.39 d 0.25 0.05 (4) 3 Single vegetative obstruction 3.1 At or below 1 GHz Equation (1) does not apply for a radio path obstructed by a single vegetative obstruction where both terminals are outside the vegetative medium, such as a path passing through the canopy of a sing
37、le tree. At VHF and UHF, where the specific attenuation has relatively low values, and particularly where the vegetative part of the radio path is relatively short, this situation can be modelled on an approximate basis in terms of the specific attenuation and a maximum limit to the total excess los
38、s: gdAet (5) dwRxhadTxhvq6 Rec. ITU-R P.833-9 where: d : length of path within the tree canopy (m) g: specific attenuation for very short vegetative paths (dB/m) and Aet : lowest excess attenuation for other paths (dB). The restriction of a maximum value for Aet is necessary since, if the specific a
39、ttenuation is sufficiently high, a lower-loss path will exist around the vegetation. An approximate value for the minimum attenuation for other paths can be calculated as though the tree canopy were a thin finite-width diffraction screen using the method of Recommendation ITU-R P.526. It is stressed
40、 that equation (5), with the accompanying maximum limit on Aet, is only an approximation. In general it will tend to overestimate the excess loss due to the vegetation. It is thus most useful for an approximate evaluation of additional loss when planning a wanted service. If used for an unwanted sig
41、nal it may significantly underestimate the resulting interference. 3.2 Above 1 GHz For terrestrial paths, the method based on RET described in 3.2.1 should be applied to compute the effect of a single tree. For slant paths, the method based on multiple scattering theory described in 3.2.2 should be
42、applied to compute the effect of a single tree. 3.2.1 Terrestrial path In order to estimate the total field, the diffracted, ground reflected and through-vegetation scattering components are first calculated and then combined. The diffracted components consist of those over the top of the vegetation
43、 and those around the sides of the vegetation. These components and the ground reflected component are calculated using ITU-R Recommendations. The through or scattered component is calculated using a model based upon the theory of radiative energy transfer (RET). 3.2.1.1 Calculation of the top diffr
44、acted component The diffraction loss, Ltop, experienced by the signal path diffracted over the vegetation, may be treated as double isolated knife-edge diffraction for the geometry defined in Fig. 4. FIGURE 4 Component diffracted over top of vegetation jjRec. ITU-R P.833-9 7 This is calculated as fo
45、llows: )()(_ jj RxTxd i f ft o pt o p GGLL (6) where GTx() and GRx() are the losses due to angles of the diffracted wave leaving the transmit antenna and coming into the receive antenna, respectively. Ltop_diff is the total diffraction loss as calculated using the method of Recommendation ITU-R P.52
46、6 for double isolated edges. 3.2.1.2 Calculation of the side diffracted component The diffraction loss, Lsidea and Lsideb, experienced by the signal diffracted around the vegetation, may again be treated as double isolated knife-edge diffraction, for the geometry defined in Fig. 5. FIGURE 5 Componen
47、ts diffracted around the vegetation The losses are calculated using equations (7) and (8). )()(_ aRxaTxs i d e ad i f fs i d e a GGLL jj (7) and )()(_ bRxbTxs i d e bd i f fs i d e b GGLL jj (8) where GTx(a,b) and GRx(a,b) are the losses due to angles of the diffracted wave leaving the transmit ante
48、nna and coming into the receive antenna, for sides a and b, respectively. Ldiff_sidea and Ldiff_sideb are the total diffraction loss around each side found using the method of Recommendation ITU-R P.526 for double isolated edges. 3.2.1.3 Calculation of the ground reflected component It is assumed th
49、at the path is sufficiently short that the ground reflected wave may be modelled by the geometry shown in Fig. 6. jbjaj aj bS i de bS i de a8 Rec. ITU-R P.833-9 FIGURE 6 Ground reflected component To calculate the loss experienced by the ground reflected wave at the receiver, the reflection coefficient, R0, of the ground reflected signal may be calculated with a given grazing angle, qg. This is a standard method and is described in Recommendation ITU-R P.1238. The values for the permittivity and conductance are
