text: #!/usr/bin/env python3
  # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  #
  # Author: Jeremy Maurer, Raymond Hogenson & David Bekaert
  # Copyright 2019, by the California Institute of Technology. ALL RIGHTS
  # RESERVED. United States Government Sponsorship acknowledged.
  #
  # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  import numpy as np
  
  _ZMIN = np.float64(-100)   # minimum required height
  _ZREF = np.float64(15000)  # maximum requierd height
  _STEP = np.float64(15.0)     # integration step size in meters
  
  _g0 = np.float64(9.80665)
  
  
  class Zenith:
      """Special value indicating a look vector of "zenith"."""
      pass
  