def net_solar_radiation(rs, albedo=0.23):
    """
    Calculate the fraction of the solar radiation that is not reflected from
    the surface (Allen et al. 1998).

    Parameters
    ----------
    rs : float
        Solar radiation (MJ m-2 day-1).
    albedo : float, optional
        Albedo (-), default is 0.23 (value for a hypothetical
        grass reference crop.

    Returns
    -------
    float
        Net solar radiation (MJ m-2 day-1).

    """
    return (1 - albedo) * rs