1、-1-QUESTION ITU-R 202-3/3Methods for predicting propagation over the surface of the Earth(1990-2000-2007)The ITU Radiocommunication Assembly,consideringa) that the presence of obstacles on the propagation path may modify, to a large extent, themean value of the transmission loss, as well as the fadi
2、ng amplitude and characteristics;b) that, with increase in frequency, the influence of the detailed roughness of the surface of theEarth as well as that of vegetation and natural or man-made structures on or above the surface of theEarth becomes more significant;c) that propagation over high mountai
3、n ridges is sometimes of great practical importance;d) that diffraction and site shielding are of practical significance in interference studies;e) that the increase in performance and storage capacity of computers, permits thedevelopment of detailed digital terrain and clutter data bases;f) that th
4、e field strength of the ground wave for frequencies between 10 kHz and 30 MHz isgiven in Recommendation ITU-R P.368, and a computer implementation, GRWAVE, is availablefrom the Radiocommunication Study Group 3 Web page;g) that information on the phase of the ground-wave mode is required;h) that info
5、rmation on ground conductivity is often available in digital form;j) that seasonal variation of ground-wave propagation has been observed,decides that the following Question should be studied1 What is the influence of terrain irregularities, vegetation and buildings, the existence ofconducting struc
6、tures and seasonal variability, both for locations within the service area around atransmitter and for the evaluation of interference at much greater distances, on the transmission loss,polarization, group delay and angle of arrival?2 What is the additional transmission loss in urban areas?3 What is
7、 the screening provided by obstacles near a terminal, taking into account thepropagation mechanisms over the path?4 What are the conditions under which obstacle gain occurs and the short-term and long-termvariations of transmission loss under these conditions?- 2 -5 What are suitable methods and for
8、mats for describing the detailed roughness of the surfaceof the Earth including topographic features and man-made structures?6 How can terrain data bases, together with other detailed information on terrain features,vegetation and buildings be applied in the prediction of attenuation, time delay, sc
9、atter anddiffraction?7 How can quantitative relationships and statistically-based prediction methods be developedwhich treat reflection, diffraction and scatter from terrain features and buildings, as well as theinfluence of vegetation?8 What is the phase of the ground-wave mode?9 How can information on ground conductivity be made available digitally as matrix orvector information?further decides1 that the results of the above studies should be included in Recommendations and/orReports;2 that the above studies should be completed by 2010.Category: S2
