def ndvire2(b6, b8):
    """
    Normalized Difference Vegetation Index red-edge 2 narrow \
    (Fernández-Manso, Fernández-Manso and Quintano, 2016).

    .. math:: NDVIRE2 = (b8 - b6) / (b8 + b6)

    :param b6: Red-edge 2.
    :type b6: numpy.ndarray or float
    :param b8: NIR.
    :type b8: numpy.ndarray or float

    :returns NDVIRE2: Index value

    .. Tip::

       Fernández-Manso, A., Fernández-Manso, O., Quintano, C. 2016. \
       SENTINEL-2A red-edge spectral indices suitability for discriminating \
       burn severity. International Journal Of Applied Earth Observation and \
       Geoinformation 50, 170-175. doi:10.1016/j.jag.2016.03.005.
    """

    NDVIRE2 = (b8 - b6) / (b8 + b6)
    return NDVIRE2