Three-dimensional simulation of the Ring effect in observations of scattered sun light using Monte Carlo radiative transfer models
Other literature type
English
OPEN
Wagner, T.
;
Beirle, S.
;
Deutschmann, T.
(2009)
We present a new technique for the quantitative simulation of the "Ring
effect" for scattered light observations from various platforms and under
different atmospheric situations. The method is based on radiative transfer
calculations at only one wavelength λ<sub>0</sub> in the wavelength range under
consideration, and is thus computationally fast. The strength of the Ring
effect is calculated from statistical properties of the photon paths for a
given situation, which makes Monte Carlo radiative transfer models in
particular appropriate. We quantify the Ring effect by the so called
rotational Raman scattering probability, the probability that an observed
photon has undergone a rotational Raman scattering event. The Raman
scattering probability is independent from the spectral resolution of the
instrument and can easily be converted into various definitions used to
characterise the strength of the Ring effect. We compare the results of our
method to the results of previous studies and in general good quantitative
agreement is found. In addition to the simulation of the Ring effect, we
developed a detailed retrieval strategy for the analysis of the Ring effect
based on DOAS retrievals, which allows the precise determination of the
strength of the Ring effect for a specific wavelength while using the
spectral information within a larger spectral interval around the selected
wavelength. Using our technique, we simulated synthetic satellite
observation of an atmospheric scenario with a finite cloud illuminated from
different sun positions. The strength of the Ring effect depends
systematically on the measurement geometry, and is strongest if the
satellite points to the side of the cloud which lies in the shadow of the
sun.