code: def _get_th2o(self):
      if self._bh2o == 0:
          return 1.0
      return np.exp(
          -np.exp(
              self._ah2o
              + self._bh2o * np.log(self._airmass * UH2O_MODIS)
          )
      )
  
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 2 for calling the _MODISAtmosphereVariables obj's underlying member method code with example usage: obj._get_th2o() and returns: np, int