Abstract. This paper presents a general approach to quantify absorption model
uncertainty due to uncertainty in the underlying spectroscopic parameters. The
approach is applied to a widely used microwave absorption model (Rosenkranz,
2017) and radiative transfer calculations in the 20–60 GHz range, which are
commonly exploited for atmospheric sounding by microwave radiometer (MWR).
The approach, however, is not limited to any frequency range, observing
geometry, or particular instrument. In the considered frequency range,
relevant uncertainties come from water vapor and oxygen spectroscopic
parameters. The uncertainty of the following parameters is found to dominate:
(for water vapor) self- and foreign-continuum absorption coefficients, line
broadening by dry air, line intensity, the temperature-dependence exponent for
foreign-continuum absorption, and the line shift-to-broadening ratio; (for
oxygen) line intensity, line broadening by dry air, line mixing,
the temperature-dependence exponent for broadening, zero-frequency line
broadening in air, and the temperature-dependence coefficient for line mixing. The
full uncertainty covariance matrix is then computed for the set of
spectroscopic parameters with significant impact. The impact of the
spectroscopic parameter uncertainty covariance matrix on simulated
downwelling microwave brightness temperatures (TB) in the 20–60 GHz
range is calculated for six atmospheric climatology conditions. The
uncertainty contribution to simulated TB ranges from 0.30 K (subarctic
winter) to 0.92 K (tropical) at 22.2 GHz and from 2.73 K (tropical) to 3.31 K
(subarctic winter) at 52.28 GHz. The uncertainty contribution is nearly
zero at 55–60 GHz frequencies. Finally, the impact of spectroscopic
parameter uncertainty on ground-based MWR retrievals of temperature and
humidity profiles is discussed.
Параметры контура линий водяного пара при уширении гелием
