FRESCO+: an improved O2 A-band cloud retrieval algorithm for tropospheric trace gas retrievals
Item
Title (Dublin Core)
FRESCO+: an improved O2 A-band cloud retrieval algorithm for tropospheric trace gas retrievals
Description (Dublin Core)
The FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A-band) algorithm has been used to retrieve cloud information from measurements of the O<sub>2</sub> A-band around 760 nm by GOME, SCIAMACHY and GOME-2. The cloud parameters retrieved by FRESCO are the effective cloud fraction and cloud pressure, which are used for cloud correction in the retrieval of trace gases like O<sub>3</sub> and NO<sub>2</sub>. To improve the cloud pressure retrieval for partly cloudy scenes, single Rayleigh scattering has been included in an improved version of the algorithm, called FRESCO+. We compared FRESCO+ and FRESCO effective cloud fractions and cloud pressures using simulated spectra and one month of GOME measured spectra. As expected, FRESCO+ gives more reliable cloud pressures over partly cloudy pixels. Simulations and comparisons with ground-based radar/lidar measurements of clouds show that the FRESCO+ cloud pressure is about the optical midlevel of the cloud. Globally averaged, the FRESCO+ cloud pressure is about 50 hPa higher than the FRESCO cloud pressure, while the FRESCO+ effective cloud fraction is about 0.01 larger. <br><br> The effect of FRESCO+ cloud parameters on O<sub>3</sub> and NO<sub>2</sub> vertical column density (VCD) retrievals is studied using SCIAMACHY data and ground-based DOAS measurements. We find that the FRESCO+ algorithm has a significant effect on tropospheric NO<sub>2</sub> retrievals but a minor effect on total O<sub>3</sub> retrievals. The retrieved SCIAMACHY tropospheric NO<sub>2</sub> VCDs using FRESCO+ cloud parameters (v1.1) are lower than the tropospheric NO<sub>2</sub>VCDs which used FRESCO cloud parameters (v1.04), in particular over heavily polluted areas with low clouds. The difference between SCIAMACHY tropospheric NO<sub>2</sub> VCDs v1.1 and ground-based MAXDOAS measurements performed in Cabauw, The Netherlands, during the DANDELIONS campaign is about −2.12×10<sup>14</sup>molec cm<sup>−2</sup>.
Creator (Dublin Core)
Wang, P.
Stammes, P.
der A, R.
Pinardi, G.
Roozendael, M.
Date (Dublin Core)
2018-01-15
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-8-6565-2008
https://acp.copernicus.org/articles/8/6565/2008/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
