Articles | Volume 8, issue 12
Research article
10 Dec 2015
Research article |  | 10 Dec 2015

Effective resolution concepts for lidar observations

M. Iarlori, F. Madonna, V. Rizi, T. Trickl, and A. Amodeo

Abstract. 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.

This paper discusses the determination of the effective resolution (ERes) of the vertical profiles of aerosol properties retrieved from lidar data. Large attention has been dedicated to providing an assessment of the impact of low-pass filtering on the effective range resolution in the retrieval procedure.

Short summary
Smoothing filters applied on lidar profiles reduce the resolution to a value indicated as the effective resolution (ERes). Several approaches to ERes estimation are investigated. The key result is an operative ERes calculation by ready-to-use equations. The presented procedures to assess the ERes are of general validity. The ERes equations are deemed to be used in automatic tools like the Single Calculus Chain. Several filters already employed in the lidar community are also critically analyzed.