def METHOD_NAME(self, fileName):
    """
    read in the data sets for observations, and possibly rename some
    variables and dimensions
    Parameters
    ----------
    fileName : str
        observation file name
    Returns
    -------
    dsObs : ``xarray.Dataset``
        The observational dataset
    """
    # Authors
    # -------
    # Xylar Asay-Davis
    # Load MLD observational data
    dsObs = xr.open_dataset(fileName)
    varList = [self.fieldName, 'month', 'year']
    if self.botFieldName is not None:
        varList.append(self.botFieldName)
    dsObs = dsObs[varList]
    if self.depths is not None:
        field = dsObs[self.fieldName]
        slices = []
        for depth in self.depths:
            if depth == 'top':
                slices.append(field.sel(method='nearest', z=0.).drop_vars(
                    'z'))
            elif depth == 'bot':
                slices.append(dsObs[self.botFieldName])
            else:
                level = field.sel(method='nearest', z=depth).drop_vars(
                    'z')
                slices.append(level)
        depthNames = [str(depth) for depth in self.depths]
        field = xr.concat(slices, dim='depthSlice')
        dsObs = xr.Dataset(data_vars={self.fieldName: field},
                           coords={'depthSlice': depthNames})
    return dsObs