code: def essl_moisture(img, low=1.1, high=1.6) -> None:
      r"""Low level moisture by European Severe Storms Laboratory (ESSL).
  
      Expects a mode L image with data corresponding to the ratio of the
      calibrated reflectances for the 0.86 µm and 0.906 µm channel.
  
      This composite and its colorisation were developed by ESSL.
  
      Ratio values are scaled from the range ``[low, high]``, which is by default
      between 1.1 and 1.6, but might be tuned based on region or sensor,
      to ``[0, 1]``.  Values outside this range are clipped.  Color values
      for red, green, and blue are calculated as follows, where ``x`` is the
      ratio between the 0.86 µm and 0.905 µm channels:
  
      .. math::
  
          R = \max(1.375 - 2.67 x, -0.75 + x) \\
          G = 1 - \frac{8x}{7} \\
          B = \max(0.75 - 1.5 x, 0.25 - (x - 0.75)^2) \\
  
      The value of ``img.data`` is modified in-place.
  
      A color interpretation guide is pending further adjustments to the
      parameters for current and future sensors.
  
      Args:
          img: XRImage containing the relevant composite
          low: optional, low end for scaling, defaults to 1.1
          high: optional, high end for scaling, defaults to 1.6
      """
      ratio = img.data
      if _is_fci_test_data(img.data):
          # Due to a bug in the FCI pre-launch simulated test data,
          # the 0.86 µm channel is too bright.  To correct for this, its
          # reflectances should be multiplied by 0.8.
          ratio *= 0.8
  
      with xr.set_options(keep_attrs=True):
          ratio = _scale_and_clip(ratio, low, high)
          red = _calc_essl_red(ratio)
          green = _calc_essl_green(ratio)
          blue = _calc_essl_blue(ratio)
          data = xr.concat([red, green, blue], dim="bands")
          data.attrs["mode"] = "RGB"
          data["bands"] = ["R", "G", "B"]
      img.data = data
  
file_path: satpy/satpy/enhancements/atmosphere.py
imports: import datetime
  import dask.array
  import xarray
label_desc: Use image node_id 1 for calling a global function with example usage: essl_moisture(img, low, high) without return types