def temp_separation_tac(T_c, T_s, fc, T_air, r_ah, r_s, r_x):
    """Compute air temperature at the canopy interface

    Parameters
    ----------
    T_c : ee.Image
        Canopy temperature (Kelvin).
    T_s : ee.Image
        Soil temperature (Kelvin).
    fc
    T_air : ee.Image
    r_ah : ee.Image
    r_s : ee.Image
    r_x : ee.Image

    Returns
    -------
    T_ac : ee.Image
        Air temperature at the canopy interface (Kelvin).

    """
    T_ac = fc.expression(
        '((T_air / r_ah) + (T_s / r_s) + (T_c / r_x)) / ((1 / r_ah) + (1 / r_s) + (1 / r_x))'
        , {'r_ah': r_ah, 'r_s': r_s, 'r_x': r_x, 'T_c': T_c, 'T_s': T_s,
        'T_air': T_air})
    return T_ac
