#1




What is the best way to determine the climatic factor (cf) in the Barnett & Vigants reliability formula? Not the C Factor!
Standard values seem to vary from 0.5 to 1 and 2. How can we determine the exact value depending on the climatic conditions of a specific area? I am especially looking for many areas in the province of Quebec in Canada. Where can I find a climatic factor map? Thanks! 
#2




VigantsBarnett reliability method
Maybe maps for the climatic factor cf do not exist (are not published). Then use instead the C factor with associated maps. The C factor is also by definition equal to cf for average terrain rouhness S = 15.2m
For a more detailed calculation you can use one of the newer ITUR P.530 reliability methods. These are applicable worldwide. Regards, Lars HL 
#3




Climatic factor
Thanks a lot Lars for your reply and your suggestion about the climatic factor for reliability calculation.
I only began to compare the ITU530 methods with the Barnett & Vigants method. Which method is the more reliable after you? 5306 or 5307/8 or the newest 5309 ? I get similar results when the path inclination is near 0 mr, but I get very different results when the path inclination is about 10 mr. What do you think about this? Thanks a lot for your collaboration. 
#4




climatic factor
ITU made a lot of changements over the last years for the recommendation P530. Therefore, if you are sure what kind of parameter set for the Barnett&Vigants is correct for your area you can choose this model.
If you have no idea the P5309 recommendation gives a detailed model where you only need the data provided by ITU and the GTopo30 DTM from USGS to get the right parameters. You do not have to look anywhere else. This model seems to be proved with hundreds of hops all over the world. Nevertheless there will be a new recommendation P53010 soon. Let's see what will be new this time. mike 
#5




Reliability methods
Rejean, here is my comments to the three ITUR P.530 reliability methods implemented in PL4.
P.5306(detailed planning)uses an average grazing angle which for many(most) paths is ambiguous or even meaningless. P.5307/8 does away with this average grazing angle. Instead many link classes are introduced, which makes it somewhat cumbersome, especially for coastal links. P.5309/10 (detailed link design)uses a terrain database (GTopo30) and the refractivity gradient data are incorporated in PL4. This makes the method convenient in use, but the method itself and/or the PL4 implementation may be unreliable (see the thread in this user forum initiated on Sep.13, 2002 by AK). At present I regard P.5307/8 to be the most reliable method. 
#6




Climatic Factor...
Thanks a lot Mike for your reply.
I will use both methods (Barnett & Vigants as well as ITU 5309) and compare them on each link. Then I will probably be able to take a better decision. Best regards! 
#7




Climatic Factor
Dear Lars,
Thanks for your comments about each ITU method. The main point I am wondering about is why the path inclination has such an effect on the reliability result? ITU 5306 and 5307/8 are the only two methods using this parameter. I get 99.9999% compared to 99.999% if the path inclination is respectively 10 mr instead of about 1 mr. Is it the reality? 
#8




inclination
In general a high low path is more reliable than a path without any inclination. The reason for this is the less high probability for multipath with a certain inclination.
mike 
#9




Path inclination and ITUR
I would also like to say that I see version 7/8 more reliable than version 9/10 in the clculation of the Geoclimatic factor, because in the calculation in 9/10 they refere to the GTOPO 30 DEM wich proved to be very unreliable.
and there is no dought that the path inclination in a very important parameter in the calculation of the Geoclimatic factor. 
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