Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign
In this study, vertical profiles and column-integrated aerosol properties retrieved by the GRASP (Generalized Retrieval of Atmosphere and Surface Properties) algorithm are evaluated with in situ airborne measurements made during the ChArMEx-ADRIMED field campaign in summer 2013. In the framework...
Main Authors: | , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-11-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | https://www.atmos-meas-tech.net/10/4439/2017/amt-10-4439-2017.pdf |
Summary: | In this study, vertical profiles and column-integrated aerosol properties
retrieved by the GRASP (Generalized Retrieval of Atmosphere and Surface
Properties) algorithm are evaluated with in situ airborne measurements made
during the ChArMEx-ADRIMED field campaign in summer 2013. In the framework of
this campaign, two different flights took place over Granada (Spain) during a
desert dust episode on 16 and 17 June. The GRASP algorithm, which
combines lidar and sun–sky photometer data measured at Granada, was
used to retrieve aerosol properties. Two sun-photometer datasets are
used: one co-located with the lidar system and the other in the Cerro
Poyos station, approximately 1200 m higher than the lidar system but at a
short horizontal distance.
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Column-integrated aerosol microphysical properties retrieved by GRASP are
compared with AERONET products showing a good agreement. Differences between
GRASP retrievals and airborne extinction profiles are in the range of 15 to
30 %, depending on the instrument on board the aircraft used as reference.
On 16 June, a case where the dust layer was coupled to the aerosol
layer close to surface, the total volume concentration differences between
in situ data and GRASP retrieval are 15 and 36 % for Granada and Cerro
Poyos retrievals, respectively. In contrast, on 17 June the
dust layer was decoupled from the aerosol layer close to the surface, and the
differences are around 17 % for both retrievals. In general, all the
discrepancies found are within the uncertainly limits, showing the
robustness and reliability of the GRASP algorithm. However, the better agreement
found for the Cerro Poyos retrieval with the aircraft data and the vertical
homogeneity of certain properties retrieved with GRASP, such as the
scattering Ångström exponent, for cases with aerosol layers
characterized by different aerosol types, shows that uncertainties in the
vertical distribution of the aerosol properties have to be considered.
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The comparison presented here between GRASP and other algorithms
(i.e. AERONET and LIRIC) and with airborne in situ measurements shows the
potential to retrieve the optical and microphysical profiles of the
atmospheric aerosol properties. Also, the advantage of GRASP versus LIRIC is that GRASP does not assume the results of the AERONET inversion as a starting point. |
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ISSN: | 1867-1381 1867-8548 |