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Effective resolution concepts for lidar observations
摘要： Since its establishment in 2000, EARLINET (European Aerosol Research Lidar NETwork) has provided, through its database, quantitative aerosol properties, such as aerosol backscatter and aerosol extinction coefficients, the latter only for stations able to retrieve it independently (from Raman or high-spectral-resolution lidars). These coefficients are stored in terms of vertical profiles, and the EARLINET database also includes the details of the range resolution of the vertical profiles. In fact, the algorithms used in the lidar data analysis often alter the spectral content of the data, mainly acting as low-pass filters to reduce the high-frequency noise. Data filtering is described by the digital signal processing (DSP) theory as a convolution sum: each filtered signal output at a given range is the result of a linear combination of several signal input data samples (relative to different ranges from the lidar receiver), and this could be seen as a loss of range resolution of the output signal. Low-pass filtering always introduces distortions in the lidar profile shape. Thus, both the removal of high frequency, i.e., the removal of details up to a certain spatial extension, and the spatial distortion produce a reduction of the range resolution.
关键词： lidar,EARLINET,low-pass filtering,effective resolution,aerosol properties
更新于2025-09-10 09:29:36
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Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece
摘要： In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years 2003-2017. For this purpose, measurements of two independent instruments, a lidar and a sun photometer, were deployed. These two instruments represent two individual networks, the European Lidar Aerosol Network (EARLINET) and the Aerosol Robotic Network (AERONET). They include different measurement schedules. Fourteen years of lidar and sun photometer measurements were analyzed in order to obtain the annual cycles and trends of multiple optical and geometrical aerosol properties in the boundary layer, in the free troposphere and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing AOD355nm trends of -21.0% and -16.6% per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets respectively. Therefore, the analysis implies that the EARLINET sampling schedule can be quite effective in producing data that can be applied to climatological studies. It has also been confirmed that the observed decreasing trend is mainly attributed to changes in the aerosol properties inside the boundary layer. Seasonal profiles of the most dominant aerosol mixture types have been generated from the lidar data. The higher values of the extinction at 355nm appear in summer, while the lower ones appear in winter. The dust component is much more dominant in the free troposphere than in the boundary layer during summer, while the opposite is observed in winter. The strongest biomass burning episodes tend to occur during summer in the free troposphere and are probably attributed to wildfires rather than agricultural fires that are predominant during spring and autumn. This kind of information can be quite useful for applications that require a priori aerosol profiles. For instance, they can be utilized in models that require aerosol climatological data as input, in the development of algorithms for satellite products, and also in passive remote sensing techniques that require knowledge of the aerosol vertical distribution.
关键词： aerosol optical properties,EARLINET,climatology,AERONET,Thessaloniki
更新于2025-09-10 09:29:36