Rainfall Rate Duration Study for Performance Assessment of Satellite Communication Links

The duration of rainfall events as a function of precipitation rate is investigated in this paper. The experimental data used in this study were measured along a rain gauge network with 8 pluviographs located in the Amazon region. The most important point to be highlighted in this study is the evidence of a correlation between rain and fade events durations observed in a 12？GHz satellite link. This result is quite important under the engineering point of view, once it can be used in the design of improvement techniques for low availability satellite systems. 1. Introduction In the planning of low availability satellite systems, an outage of 1% to 0.1% in the worst month is normally acceptable. In these systems the temporal variability of fading has a strong impact on system design. Consequently, the knowledge of rain dynamics is of fundamental relevance. It is recognized that the conversion of rain rate duration to slant path duration statistics is not an easy task [1]. The main problems are the vertical nonhomogeneity of rain structure and the possibility of having more than one rain cell along the propagation path. However, according to Timothy et al. [2], if the vertical distribution of rain is uniform from the earth surface to a height near the 0° isotherm level and the elevation angle is higher than 30°, the measured rainfall rate threshold at a given probability level may be used to obtain information on the dynamics associated with the attenuation in slant path. A study by Lekkla and Prapinmongkolkarn [3] corroborates this assertion. In this context, based on measurements carried out in the Brazilian Amazon region, this paper investigates the duration of rainfall events as a function of precipitation rate. Figure 1 shows the rain gauge network used in the study described here and details about these sites are presented in Table 1. Table 1: Description of the experimental sites. Figure 1: Rain gauge network. 2. Rainfall Rate Events Duration Statistics In each site shown in Figure 1, measurements of rain duration were carried out for a total period of one year between 2003 and 2005. The integration time of precipitation rate was 10s to be near the instantaneous value and more adequate to be aligned with the dynamics of signal attenuation. An example of rain duration statistics for the 8 sites illustrated in Figure 1 and a rain rate threshold of 50？mm/h is depicted in Figure 2. It is noted that, with only one exception, all the other sites have shown the same behaviour. The exception was in the site of Cruzeiro do Sul [7°36′S; 72°40′W] where a large