def datt3(b3, b5, b8a):
    """
    Vegetation Index proposed by Datt 3 (Datt, 1998).

    .. math:: DATT3 = b8a / (b3 * b5)

    :param b3: Green.
    :type b3: numpy.ndarray or float
    :param b5: Red-edge 1.
    :type b5: numpy.ndarray or float
    :param b8a: NIR narrow.
    :type b8a: numpy.ndarray or float

    :returns DATT3: Index value

    .. Tip::

       Datt, B. 1998. Remote sensing of chlorophyll a, chlorophyll b, \
       chlorophyll a + b, and total carotenoid content in eucalyptus leaves. \
       Remote Sensing of Environment, 66, 111-121. \
       doi:10.1016/S0034-4257(98)00046-7.
    """

    DATT3 = b8a / (b3 * b5)
    return DATT3