def get_fai(b):
    return b['b2'].subtract(b['b1'].add(b['b5'].subtract(b['b1']).multiply((859.0 - 645) / (1240 - 645)))).select(['sur_refl_b02'], ['b1'])
Just the internals of the FAI method
dataset/ETHPy150Open nasa/CrisisMappingToolkit/cmt/modis/simple_modis_algorithms.py/get_fai