def calc_rain_kdp_zdr(kdp, zdr, a=90.8, b=0.93, c=-0.169):
    """
    kdp = Specific Differential Phase (deg km^-1)
    zdr = Differential Reflectivity (dB)
    a, b, c = Adjustable function parameters
    """
    return a * kdp ** b * 10.0 ** (c * zdr)
