Abstract. To evaluate the SEVIRI retrieval for aerosols above
clouds presented in Part 1 of the companion paper, the algorithm is applied
over the south-east Atlantic Ocean during the CLARIFY-2017 field campaign
period. The first step of our analysis compares the retrieved aerosol and
cloud properties against equivalent products from the MODIS MOD06ACAERO
retrieval (Meyer et al., 2015). While the correlation between the two
satellite retrievals of the above-cloud aerosol optical thickness (AOT) is
good (R = 0.78), the AOT retrieved by SEVIRI is 20.3 % smaller than that
obtained from the MODIS retrieval. This difference in AOT is attributed
mainly to the more absorbing aerosol model assumed for the SEVIRI retrieval
compared to MODIS. The underlying cloud optical thickness (COT) derived from
the two satellites is in good agreement (R = 0.90). The cloud droplet
effective radius (CER) retrieved by SEVIRI is consistently smaller than
MODIS by 2.2 µm, which is mainly caused by the use of different
spectral bands of the satellite instruments. In the second part of our
analysis, we compare the forecast water vapour profiles used for the SEVIRI
atmospheric correction as well as the aforementioned aerosol and cloud
products with in situ measurements made from the Facility for Airborne
Atmospheric Measurements (FAAM) aircraft platform during the CLARIFY-2017
campaign. Around Ascension Island, the column water vapour used to correct
the SEVIRI signal is overestimated by 3.1 mm in the forecast compared to
that measured by dropsondes. However, the evidence suggests that the
accuracy of the atmospheric correction improves closer to the African coast.
Consistency is observed between the SEVIRI above-cloud AOT and in situ
measurements (from cavity ring-down spectroscopy instruments) when the
measured single-scattering albedo is close to that assumed in the retrieval
algorithm. On the other hand, the satellite retrieval overestimates the AOT
when the assumed aerosol model is not absorbing enough. Consistency is also
found between the cloud properties retrieved by SEVIRI and the CER measured
by a cloud droplet probe and the liquid water path derived from a microwave
radiometer. Despite the instrumental limitations of the geostationary
satellite, the consistency obtained between SEVIRI, MODIS and the aircraft
measurements demonstrates the ability of the retrieval in providing
additional information on the temporal evolution of the aerosol properties
above clouds.
Effect of the Aerosol Model Assumption on the Atmospheric Correction over Land: Case Studies with CHRIS/PROBA Hyperspectral Images over Benelux