CALIOP near-real-time backscatter products compared to EARLINET data

Abstract

Abstract. The expedited near-real-time Level 1.5 CloudAerosol Lidar with Orthogonal Polarization (CALIOP) version 3 products were evaluated against data from the groundbased European Aerosol Research Lidar Network (EAR-LINET). The statistical framework and results of the threeyear evaluation of 48 CALIOP overpasses with ground tracks within a 100 km distance from operating EARLINET stations are presented and include analysis for the following CALIOP classifications of aerosol type: dust, polluted dust, clean marine, clean continental, polluted continental, mixed and/or smoke/biomass burning. For the complete data set comprising both the planetary boundary layer (PBL) and the free troposphere (FT) data, the correlation coefficient (R) was 0.86. When the analysis was conducted separately for the PBL and FT, the correlation coefficients were R = 0.6 and R = 0.85, respectively. From analysis of selected specific cases, it was initially thought that the presence of FT layers, with high attenuated backscatter, led to poor agreement of the PBL backscatter profiles between the CALIOP and EARLINET and prompted a further analysis to filter out such cases; however, removal of these layers did not improve the agreement as R reduced marginally from R = 0.86 to R = 0.84 for the combined PBL and FT analysis, increased marginally from R = 0.6 up to R = 0.65 for the PBL on its own, and decreased marginally from R = 0.85 to R = 0.79 for the FT analysis on its own. This suggests considerable variability, across the data set, in the spatial distribution of the aerosol over spatial scales of 100 km or less around some EARLINET stations rather than influence from elevated FT layers. For specific aerosol types, the correlation coefficient between CALIOP backscatter profiles and the EARLINET data ranged from R = 0.37 for polluted continental aerosol in the PBL to R = 0.57 for dust in the FT.

EARLINET evaluation of the CATS Level 2 aerosol backscatter coefficient product

“…In order to evaluate the CATS Level 2 aerosol backscatter product at 1064 nm, we utilized backscatter coefficient profiles calculated either with the SCC algorithm or, in case of PollyXT lidar systems, with independently developed userassisted retrieval algorithms (Baars et al, 2016). The EAR-LINET backscatter coefficient profiles used in this study are calculated with the SCC version 4 algorithm (for the stations that are not part of PollyNET) and with the methodology described in Haarig et al (2017; for the stations that are part of PollyNET). The SCC algorithm (D'Amico et al, 2015(D'Amico et al, , 2016Mattis et al, 2016) is developed with the concept of sustaining the homogeneity of aerosol products derived from different EARLINET lidar systems while satisfying the need for coordinated, quality-assured measurements.…”

“…The comparison showed that by using only the signal from the elastic channels, the mean relative deviation in the calculation of the aerosol backscatter coefficient at 1064 nm is less than 30 % (Althausen et al, 2009;Baars et al, 2012;Engelmann et al, 2016;Hänel et al, 2012), thus meeting the quality-assurance requirements of EARLINET. None of the lidar systems participating in the present study are equipped with a rotational-vibrational Raman channel excited by the 1064 nm, as, for example, recently reported by Haarig et al (2017). In the case of Pol-lyXT lidars, for the daytime backscatter coefficient calculations, the Fernald-Klett method (Klett, 1981;Fernald, 1984) is implemented, assuming a height-independent lidar ratio.…”

A Geostationary Instrument Simulator for Aerosol Observing System Simulation Experiments

“…For certain applications of the G5NR data, such as sampling studies to quantify the likelihood that an orbit will encounter certain aerosol mixtures, it is recommended that users apply these scaling factors to adjust the speciated AOD 550 . G5NR simulated aerosol vertical distributions were compared to cloud-cleared CALIOP Level 1.5 aerosol attenuated backscatter vertical profile data [34] in Figures 5 and 6. This is a spatially averaged cloud cleared product suitable for comparison to aerosol transport models.…”

Comparison of backscatter coefficient at 1064nm from CALIPSO and ground-based ceilometers over coastal and non-coastal regions

“…CALIOP, along with two other instruments, is on board a polar-orbit satellite called CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) [13]. Over the past years, several different comparison studies between CALIOP and ground-based lidars were performed by various research groups using different approaches [7,11,[14][15][16]. Some of them followed the criterion established in the CALIPSO validation plan and considered only measurements that were taken when the satellite was passing over the ground-stations within 100 km distance [7].…”