added interp_atten. Function to interpolate reference attenuation to invalid beams. Not yet tested.
added interp_atten. Function to interpolate reference attenuation to invalid
beams. Not yet tested.

kmuehlbauer/wradlib,heistermann/wradlib,wradlib/wradlib,wradlib/wradlib,kmuehlbauer/wradlib,heistermann/wradlib