def dt642epoch(dt64):
    """
    Convert numpy.datetime64 array to epoch time 
    (seconds since 1/1/1970 00:00:00)

    Parameters
    ----------
    dt64 : numpy.datetime64
        Single or array of datetime64 object(s)

    Returns
    -------
    time : float
        Epoch time (seconds since 1/1/1970 00:00:00)

    """
    return dt64.astype('datetime64[ns]').astype('float') / 1e9