code: def dsr_thurai_2007(D_eq):
      
  
      if D_eq < 0.7:
          return 1.0
      elif D_eq < 1.5:
          return 1.173 - 0.5165*D_eq + 0.4698*D_eq**2 - 0.1317*D_eq**3 - \
              8.5e-3*D_eq**4
      else:
          return 1.065 - 6.25e-2*D_eq - 3.99e-3*D_eq**2 + 7.66e-4*D_eq**3 - \
              4.095e-5*D_eq**4
docs: Drop shape relationship function from Thurai2007
      (http://dx.doi.org/10.1175/JTECH2051.1) paper.
      Arguments:
          D_eq: Drop volume-equivalent diameter (mm)
  
      Returns:
          r: The vertical-to-horizontal drop axis ratio. Note: the Scatterer class
          expects horizontal to vertical, so you should pass 1/dsr_thurai_2007