Elena Saltikoff, FMI:
Atteanuation by precipitation
Intervening precipitation between the radar and the target causes some attenuation. For S-band, this is often negligble, for X-band it's often fatal but for C-band (operationally used in Northern Europe) an intelligent correction algorithm makes a difference.
A typical algorithm gives corrected values (dBZc) by tuning two parameters (constant C and exponent E) in the equation
dBZc = dBZ + 2C*r*SUM(ZE)
For C-band system and liquid precipitation, the suggested values are for constant C 0.000112 dB/km and exponent E 0.62
It is not enough to set parameters C and E. As the ”right” values vary case to case, there is a risk of cumulating too huge corrections so a maximum cumulative correction to one pixel must be set.
An optimal attenuation correction system would have different constants for snow and water, and a dynamical switch to change the melting layer. This would need as an input a 3-dimensional field of water phase of hydrometeors.
Also, in case of hail, the attenuation correction can be overestimated as dBZ values are bigger than for rain of same attenuation effect. One way to get round this is to set maximum dBZ for correction (e.g.50 dBZ so that any pixels with reflectivity bigger than 50 dBZ are treated as 50 dBZ) . The more proper way would be target identification (dual polarization or Holleman-Waldvogel method).