code: def get_coeff_by_sfc(coeff_fn, bt_data, idx):
      """Read coefficients for specific filename (land or sea)."""
      sfc_coeff = read_atms_limb_correction_coefficients(coeff_fn)
      # transpose bt_data for correction
      bt_data = bt_data.transpose("Channel", "y", "x")
      c_size = bt_data[idx, :, :].chunks
      correction = da.map_blocks(
          apply_atms_limb_correction,
          bt_data,
          idx,
          *sfc_coeff,
          chunks=c_size,
          meta=np.array((), dtype=bt_data.dtype),
      )
      return correction
  
imports: import datetime
  import importlib
  import logging
  import os
  from collections import Counter
  import dask.array
  import numpy
  import xarray
  from satpy.aux_download import retrieve
  from satpy.readers.file_handlers import BaseFileHandler
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 5 for calling a global function with example usage: get_coeff_by_sfc(coeff_fn, bt_data, idx) and returns: correction