G. Delrieu et al., Quantification of path-integrated attenuation for X- and C-band weather radar systems operating in Mediterranean heavy rainfall, J APPL MET, 39(6), 2000, pp. 840-850
The aim of the current study is to quantify attenuation effects that X- and
C-band weather radar systems may experience in heavy rainfall. Part of thi
s information can be obtained from power-law relationships between the atte
nuation coefficient k (dB km(-1)) and the rain rate R (mm h(-1)). These rel
ations exhibit a strong dependence on the wavelength used and a significant
influence of the raindrop size and temperature distributions. Here the pur
pose is to go one step further by providing estimates of the path-integrate
d attenuations (PIAs) that could be observed as a function of range for a g
iven wavelength. Obviously, these values depend on the space and time struc
ture of rainfall and, therefore, refer to a given climatological context. T
he methodology used consists of using k-R relations to downgrade carefully
processed S-band radar data to the corresponding X- and C-band signals. The
data were collected in the Cevennes region, a Mediterranean region in Fran
ce subject to intense and long-lasting rain events during the autumn season
. A refined data processing procedure was applied to the available reflecti
vity measurements, including ground-clutter removal and correction for the
effects of the vertical profile of reflectivity as well as a final bias adj
ustment using rain gauge data. For three rain events, 75 h of instantaneous
rain-rate fields thus were available with total rain amounts that exceeded
300 mm over most of the area of interest. Examples of attenuated profiles
are presented, and PIA-range-frequency curves are established for the two w
avelengths considered under various hypotheses that concern the raindrop si
ze distribution. One of the results is that, at C band, a PIA of 3 dB is ex
ceeded for 5% of the rain-rate profiles at a range of 50 km. Another findin
g is that a multiplicative factor of about 6 exists between C- and X-band a
ttenuation effects. Implications for rain-rate estimation at X- and C band
are discussed.