code: def _get_to3(self):
      if self._ao3 == 0:
          return 1.0
      return np.exp(-self._airmass * UO3_VIIRS * self._ao3)
  
imports: from __future__ import annotations
  import logging
  from typing import Optional, Type, Union
  import dask.array
  import numpy
  import xarray
  from satpy.dataset.dataid import WavelengthRange
label_desc: Use image node_id 3 for calling the _VIIRSAtmosphereVariables obj's underlying member method code with example usage: obj._get_to3() and returns: np, int