Development of Rain Attenuation and Rain Rate Maps for Satellite Communications System Design in Greece Anastassios D Papatsoris*(1), Konstantinos Polimeris(1) and Athanasia A Lazou(2) (1) TEI of Serres, Department of Informatics & Communications, Terma Magnesias, 62124 Serres, Greece (2) Foundation of National Social Security, Division of Engineering, Aristotelous 15, 54624 Thessaloniki, Greece E-mail:
[email protected] Abstract Using six (6) years of point rainfall data from several locations in Greece, which were obtained from the National Hellenic Meteorological Service (NHMS)1, the statistics of rainfall for various percentages of time for the average year are derived. Using the originally derived rainfall statistics2, accurate rain rate and attenuation maps are developed for facilitating satellite communications systems design in Greece. Introduction The effect of local climatology on the performance of satellite communication systems operating at the Ku-band and especially in the Ka-band is very important. One of the most widely used methodologies for assessing the radiowave propagation impairments on satellite communications systems, is outlined in Recommendation ITU-R 618-9 [1]. In order to assess the most critical aspect of radiowave propagation, viz. rain attenuation, the Recommendation dictates detailed knowledge of the statistics of rainfall at the location where the Earth station is going to be installed. Nevertheless, due to the absence of such rain statistics in Greece, radio systems engineers are currently relying on Recommendation ITU-R P.837-5 [2]. Recommendation ITU-R P.837-5 contains maps of R0.01%, i.e., the rainfall rate exceeded for 0.01% of the average year, which have been generated by suitable processing of the ERA-40 re-analysis database. It gives also a methodology for assessing rainfall rates exceeded for other percentages of time. And despite the fact Rec. ITU-R P.837-5 is a valuable tool to the hands of the radio systems engineer, it is still no substitute for local long-term measurements of rainfall rate, from which accurate local statistics of rainfall are deriving from. In this paper, results from the statistical processing of long-term measurements of rainfall rate in Greece are reported for the first time in the literature, and subsequently rainfall rate contour maps and example rain attenuation maps applicable to satellite communications systems operating at the Ka-band 20/30GHz are given. Development of Rainfall Rate and Attenuation Maps For the construction of rainfall rate maps for various percentages of time of the average year, data records for 12 locations in Greece and for 6 years from 2000 to 2005 were processed. A detailed description of the locations, the available rainfall data as well as the derivation of the R0.01% parameter referring to integration time of 1-min has been 1
We would like to thank the National Hellenic Meteorological Service (HNMS) for providing us with the rainfall rain data and express our gratitude to Dr. Manolis Anadranistakis for facilitating our effort. 2 This work was co-funded by the European Social Fund and National Resources - (EPEAEK-II) ARXIMHDHS.
978-1-4244-2042-1/08/$25.00 ©2008 IEEE
given in [3]. Therefore, here we concentrate on reporting results for percentages of time related to satellite communication systems operating at the Ku-band and Ka-band and for common lower availabilities, viz. 99.95% and 99.9%. The cumulative distribution of rainfall rate for 1-min integration time was obtained by converting the available from our data cumulative distribution for 5-min integration time, using the relation suggested in [2]. In Table 1 the results for the rainfall rate exceeded for 0.1% and 0.05% of the average year for the 12 locations of Greece are tabulated. For the sake of comparison, the corresponding values from ITU-R P.837-5 are also shown.
Location Agrinio Alexandroupolis Hellinikon Heraklion Ioannina Lamia Larisa Limnos Milos Pirgos Serres Chios Country average
Lat/ Long [deg] 38°36’ 21°21’ 40°51’ 25°57’ 37°53’ 23°44’ 35°20’ 25°10’ 39°41’ 20°49’ 38°54’ 22°16’ 39°39’ 22°26’ 39°55’ 25°14’ 36°43’ 24°30’ 37°55’ 21°17’ 41°06’ 23°34’ 38°20’ 26°48’
Elevation [m]
R0.1% [mm/hr]
ITU R0.1% [mm/hr]
R0.05% [mm/hr]
ITU R0.05% [mm/hr]
24
13.00
13.20
19.81
22.17
3
10.32
8.05
15.71
13.23
40
7.65
11.16
13.00
18.90
39
10.32
12.22
14.36
24.26
483
13.00
11.80
19.81
19.34
12
7.65
9.14
11.66
14.76
74
7.65
8.50
11.66
13.61
4
10.32
9.89
15.71
16.80
130
8.98
12.97
15.71
23.98
12
17.07
13.97
26.70
23.80
70
7.65
7.53
13.00
12.37
7
10.32
12.81
18.44
22.69
10.33
10.94
16.30
18.83
Observing the derived R0.1% and R0.05% values and comparing them to those suggested by ITU-R P.837-5, differences ranging from -22% to +46% and from -16% to +69% are observed, respectively. Nevertheless, careful inspection of Table 1 reveals good agreement in general between local point rainfall statistics and ITU's model, with the exception of few isolated cases. Indeed, in terms of national rain rate averages, the agreement is within +16% and 6% for R0.1% and R0.05%, accordingly. The even spatial distribution of the geographical locations across the latitude and longitude boundaries of Greece, allows the construction of rain rate maps depicting R0.1% and R0.05% isohyets. The corresponding maps are illustrated in Figures 1 and 2, respectively.
Finally, rain attenuation maps for a geostationary satellite located at 335.5E and associated VSAT configuration operating at the Ka-band in Greece are given in Figure 3.
Figure 1. Rain rate (mm/hr) exceeded for 0.1% of the average year in Greece.
Figure 2. Rain rate (mm/hr) exceeded for 0.05% of the average year in Greece.
Figure 3. Rain attenuation contour maps at 20 GHz (a) and 30 GHz (b) for 99.95% system availability for a geostationary satellite located at 335.5E and associated VSAT network installed in Greece. The attenuation calculations shown here have been done adopting the methodology of ITU outlined in Recommendation ITU-R P.618-9 [1]. Rain specific attenuation calculations have been done according to Recommendation ITU-R P.838-3 [4], whereas rain heights at the 12 locations in Greece have been adapted from Recommendation ITUR P.839-3 [5]. Conclusion Utilizing rainfall rate data from six recent years (2000-2005) supplied by the Hellenic National Meteorological Service, rain rates exceeded for 0.1% and 0.05% of the average year have been reported for the first time for Greece. These maps can be readily utilized by radio systems engineers to assess quickly and accurately the effect of the dominant radiowave propagation factor on satellite system design. Finally, indicative national rain attenuation maps for a VSAT system supported by a geostationary satellite located over the Atlantic Ocean and operating at the Ka-band have been given. References: [1] ITU-R Recommendation P.618-9, “Propagation data and prediction methods required for the design of Earth-space telecommunication systems”, Geneva, International Telecommunications Union, 2007. [2] ITU-R Recommendation P.837-5, “Characteristics of precipitation for propagation modeling”, Geneva, International Telecommunications Union, 2007. [3] Papatsoris A. D., Polimeris K., Sklari, I., and Lazou A. A., “Characteristics of Rainfall for Radiowave Propagation Studies in Greece”, IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting, San Diego, July 5-12, 2008. [4] ITU-R Recommendation P.838-3, “Specific attenuation model for use in prediction methods”, Geneva, International Telecommunications Union, 2005. [5] ITU-R Recommendation P.839-3, “Rain height model for prediction methods”, Geneva, International Telecommunications Union, 2001.
