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MICRO AND MACRO SCALE SPATIAL RAIN VARIATION
Part 1: Slant path attenuation for EHF systems and considerations for long and medium range diversity gain
Part 2: Dynamic millimeter wave communications in the presence of rain
Sarah Callaghan
University of Portsmouth and
Radio Communications Research Unit, RAL
Cristina Enjamio
University of Portsmouth and
University of Vigo
Macro and Micro Scales
Slant path attenuation for EHF systems and considerations for long and medium range
diversity gain
Sarah Callaghan
University of Portsmouth and
Radio Communications Research Unit, RAL
Introduction
Attenuation statistics measured in the South of England for Ku, Ka
and V-band
Satellite systems operating at EHF frequencies are very affected by the
presence of rain, light rain and clouds along the slant path.
•Attenuation is unlikely to be compensated for by available fade margin alone.
•Therefore need to design effective fade mitigation techniques
•Two major techniques are:
•Time diversity
•Site diversity
To effectively design fade mitigation techniques, it is necessary to accurately model the spatial and temporal structure of rain.
STENTOR Experiment
Artist's impression of STENTOR
Due for launch end 2001.
Beacon frequencies 20.7 and 41.4 GHz Schematic map of locations of
beacon receivers
Chilbolton Advanced Meteorological Radar.
• 25 m steerable antenna• 3 GHz Doppler-Polarization radar• operational range of 100 km• beam width of 0.25 degrees• max angular velocity 1 degree / second
CAMRa
• recorded on the 1st May 2001• 124 near horizontal scans• measured over an angle of 80 degrees• interpolated onto a square Cartesian grid, with a grid spacing of 300m and a side length of 56.2km• data points2188
Storm event: Details
• Contours of equal (log) rain rate
• used MATLAB’s predefined contour function at specific values of (log) rain rate to determine contour lines
Box counting method:
Count number of boxes required to cover length of each contour line.
Repeat, using boxes of different side lengths.
Plot on graph as ln(1/box size) vs ln(number of boxes).
Slope of best fit line is box counting dimension.
Box counting results for raster 25 (for each separate contour line having more than 100 vertices)
Sample values for different contour values
Contour values Box counting(log rain rate) dimension1 1.120.75 1.230.5 1.210.25 1.15-0.25 1.21-0.5 1.15-0.75 1.18-1 1.24
Box counting results for all contours in raster 25
Contour values Box counting(log rain rate) dimension1 1.180.75 1.230.5 1.250.25 1.25-0.25 1.28-0.5 1.23-0.75 1.13-1 1.15
Contour values Box counting(log rain rate) dimension1 1.170.75 1.220.5 1.250.25 1.28-0.25 1.26-0.5 1.20-0.75 1.15-1 1.17
Box counting dimension for all rasters in storm event.
Radar picture from CAMRa taken along
slant path to ITALSAT
Corresponding attenuation time series experienced by beacon
on ITALSAT
Concluding remarks
• Slant path systems operating at EHF suffer from attenuation that cannot be compensated for by available fade margin alone.
• Need to further understand and accurately model spatial and temporal distribution of rain.
• Fractal nature of rain rate contours has been established, confirming other work done on the fractal nature of the spatial variation of rain.
• Work ties in with others working on different scales, working towards a global understanding covering micro and macro scales.
References
• Lovejoy, S., Area-Perimeter Relation for Rain and Cloud Areas, Science, Vol 216, 185-187, April 1982
• Rys, F.S., Waldvogel, A. Fractal Shape of Hail Clouds, Physical Review Letters, Vol. 56, Number 7, 784-787, February 1986
• Klinkenberg, B., A fractal analysis of shadowed and sunlit areas, Int. Jnl. Remote Sensing, Vol. 15, No. 5, 967-977, 1994
