Paper Info
Title
Development and Application of HECORA Cloud Retrieval Algorithm Based On the O2-O2 477 nm Absorption Band.
Abstract
In this paper, we present the Hefei EMI Cloud Retrieval Algorithm (HECORA), which uses information from the O-2-O-2 absorption band around 477 nm to retrieve effective cloud fraction and effective cloud pressure from satellite observations. The retrieved cloud information intends to improve the atmospheric trace gas products based on the Environment Monitoring Instrument (EMI) spectrometer. The HECORA method builds on OMCLDO2 and presents some evolutions. The Vector Linearized Discrete Ordinate Radiative Transfer (VLIDORT) model has been used to produce the Top of the Atmosphere (TOA) reflectance Look-up Tables (LUT) as a function of the cloud fraction and cloud pressure. Applying the Differential Optical Absorption Spectroscopy (DOAS) technique to the synthetic reflectance LUT, the reflectance spectra can be associated with O-2-O-2 geometrical vertical column densities (VCDgeo) and continuum reflectance. This is the core of the retrieval method, since there is a one-to-one relationship between O-2-O-2 VCDgeo and continuum reflectance, on the one hand, and effective cloud fraction and effective cloud pressure, on the other hand, for a given illumination and observing geometry and given surface height and surface albedo. We first used the VLIDORT synthetic spectra to verify the HECORA algorithm and obtained good results in both the Lambertian cloud model and the scattering cloud model. Secondly, HECORA is applied to OMI and TROPOMI and compared with OMCLDO2, FRESCO+, and OCRA/ROCINN cloud products. Later, the cloud pressure results from TROPOMI observations obtained using HECORA and FRESCO+ are compared with the CALIOP Cloud Layer product. HECORA is closer to the CALIOP results under low cloud conditions, while FRESCO+ is closer to high clouds due to the higher sensitivity of the O-2 A-band to cloud vertical information. Finally, HECORA is applied to the TROPOMI NO2 retrieval. Validation of the tropospheric NO2 VCD with ground-based MAX-DOAS measurements shows that choosing HECORA cloud products to correct for photon path variations on the TROPOMI tropospheric NO2 VCD retrievals has better performance than using FRESCO+ under low cloud conditions. In conclusion, this paper shows that the HECORA cloud products are in good agreement with the well-established cloud products and that they are suitable for correcting the effect of cloud in trace gas retrievals. Therefore, HECORA has the potential to be applied to EMI.
Year
DOI
Venue
2020
10.3390/rs12183039
REMOTE SENSING
Keywords
DocType
Volume
cloud fraction,cloud pressure,EMI,TROPOMI,DOAS
Journal
12
Issue
Citations 
PageRank 
18
0
0.34
References 
Authors
0
9
Name
Order
Citations
PageRank
Shuntian Wang100.34
Cheng Liu206.42
Wenqiang Zhang300.68
Nan Hao400.34
Sebastian Gimeno-Garcia500.34
Chengzhi Xing601.01
Chengxin Zhang702.37
Wenjing Su801.69
Jianguo Liu943.83