code: def Kdp(scatterer):
      
      if (scatterer.thet0 != scatterer.thet) or \
          (scatterer.phi0 != scatterer.phi):
          
          raise ValueError("A forward scattering geometry is needed to " + \
              "compute the specific differential phase.")
  
      S = scatterer.get_S()
      return 1e-3 * (180.0/np.pi) * scatterer.wavelength * (S[1,1]-S[0,0]).real
docs: Specific differential phase (K_dp) for the current setup.
  
      Args:
          scatterer: a Scatterer instance.
  
      Returns:
          K_dp [deg/km].
  
      NOTE: This only returns the correct value if the particle diameter and
      wavelength are given in [mm]. The scatterer object should be set to 
      forward scattering geometry before calling this function.